X-Git-Url: https://git.saurik.com/wxWidgets.git/blobdiff_plain/b61cc19c06d9795c73fc6fbe893e92898938c70e..87f0b1323b7ac77f02133b836c8dfee63b0fd387:/src/png/pngwutil.c?ds=sidebyside

diff --git a/src/png/pngwutil.c b/src/png/pngwutil.c
index 19feb1d98c..da18e9502e 100644
--- a/src/png/pngwutil.c
+++ b/src/png/pngwutil.c
@@ -1,8 +1,8 @@
 
 /* pngwutil.c - utilities to write a PNG file
  *
- * Last changed in libpng 1.4.1 [February 25, 2010]
- * Copyright (c) 1998-2010 Glenn Randers-Pehrson
+ * Last changed in libpng 1.5.6 [November 3, 2011]
+ * Copyright (c) 1998-2011 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
  *
@@ -11,11 +11,11 @@
  * and license in png.h
  */
 
-#define PNG_NO_PEDANTIC_WARNINGS
-#include "png.h"
-#ifdef PNG_WRITE_SUPPORTED
 #include "pngpriv.h"
 
+#ifdef PNG_WRITE_SUPPORTED
+
+#ifdef PNG_WRITE_INT_FUNCTIONS_SUPPORTED
 /* Place a 32-bit number into a buffer in PNG byte order.  We work
  * with unsigned numbers for convenience, although one supported
  * ancillary chunk uses signed (two's complement) numbers.
@@ -32,7 +32,9 @@ png_save_uint_32(png_bytep buf, png_uint_32 i)
 #ifdef PNG_SAVE_INT_32_SUPPORTED
 /* The png_save_int_32 function assumes integers are stored in two's
  * complement format.  If this isn't the case, then this routine needs to
- * be modified to write data in two's complement format.
+ * be modified to write data in two's complement format.  Note that,
+ * the following works correctly even if png_int_32 has more than 32 bits
+ * (compare the more complex code required on read for sign extention.)
  */
 void PNGAPI
 png_save_int_32(png_bytep buf, png_int_32 i)
@@ -54,6 +56,7 @@ png_save_uint_16(png_bytep buf, unsigned int i)
    buf[0] = (png_byte)((i >> 8) & 0xff);
    buf[1] = (png_byte)(i & 0xff);
 }
+#endif
 
 /* Simple function to write the signature.  If we have already written
  * the magic bytes of the signature, or more likely, the PNG stream is
@@ -74,42 +77,25 @@ png_write_sig(png_structp png_ptr)
    /* Write the rest of the 8 byte signature */
    png_write_data(png_ptr, &png_signature[png_ptr->sig_bytes],
       (png_size_t)(8 - png_ptr->sig_bytes));
+
    if (png_ptr->sig_bytes < 3)
       png_ptr->mode |= PNG_HAVE_PNG_SIGNATURE;
 }
 
-/* Write a PNG chunk all at once.  The type is an array of ASCII characters
- * representing the chunk name.  The array must be at least 4 bytes in
- * length, and does not need to be null terminated.  To be safe, pass the
- * pre-defined chunk names here, and if you need a new one, define it
- * where the others are defined.  The length is the length of the data.
- * All the data must be present.  If that is not possible, use the
- * png_write_chunk_start(), png_write_chunk_data(), and png_write_chunk_end()
- * functions instead.
- */
-void PNGAPI
-png_write_chunk(png_structp png_ptr, png_bytep chunk_name,
-   png_bytep data, png_size_t length)
-{
-   if (png_ptr == NULL)
-      return;
-   png_write_chunk_start(png_ptr, chunk_name, (png_uint_32)length);
-   png_write_chunk_data(png_ptr, data, (png_size_t)length);
-   png_write_chunk_end(png_ptr);
-}
-
 /* Write the start of a PNG chunk.  The type is the chunk type.
  * The total_length is the sum of the lengths of all the data you will be
  * passing in png_write_chunk_data().
  */
-void PNGAPI
-png_write_chunk_start(png_structp png_ptr, png_bytep chunk_name,
-   png_uint_32 length)
+static void
+png_write_chunk_header(png_structp png_ptr, png_uint_32 chunk_name,
+    png_uint_32 length)
 {
    png_byte buf[8];
 
-   png_debug2(0, "Writing %s chunk, length = %lu", chunk_name,
-      (unsigned long)length);
+#if defined(PNG_DEBUG) && (PNG_DEBUG > 0)
+   PNG_CSTRING_FROM_CHUNK(buf, chunk_name);
+   png_debug2(0, "Writing %s chunk, length = %lu", buf, (unsigned long)length);
+#endif
 
    if (png_ptr == NULL)
       return;
@@ -123,13 +109,16 @@ png_write_chunk_start(png_structp png_ptr, png_bytep chunk_name,
 
    /* Write the length and the chunk name */
    png_save_uint_32(buf, length);
-   png_memcpy(buf + 4, chunk_name, 4);
-   png_write_data(png_ptr, buf, (png_size_t)8);
+   png_save_uint_32(buf + 4, chunk_name);
+   png_write_data(png_ptr, buf, 8);
+
    /* Put the chunk name into png_ptr->chunk_name */
-   png_memcpy(png_ptr->chunk_name, chunk_name, 4);
+   png_ptr->chunk_name = chunk_name;
+
    /* Reset the crc and run it over the chunk name */
    png_reset_crc(png_ptr);
-   png_calculate_crc(png_ptr, chunk_name, 4);
+
+   png_calculate_crc(png_ptr, buf + 4, 4);
 
 #ifdef PNG_IO_STATE_SUPPORTED
    /* Inform the I/O callback that chunk data will (possibly) be written.
@@ -139,20 +128,30 @@ png_write_chunk_start(png_structp png_ptr, png_bytep chunk_name,
 #endif
 }
 
-/* Write the data of a PNG chunk started with png_write_chunk_start().
+void PNGAPI
+png_write_chunk_start(png_structp png_ptr, png_const_bytep chunk_string,
+    png_uint_32 length)
+{
+   png_write_chunk_header(png_ptr, PNG_CHUNK_FROM_STRING(chunk_string), length);
+}
+
+/* Write the data of a PNG chunk started with png_write_chunk_header().
  * Note that multiple calls to this function are allowed, and that the
  * sum of the lengths from these calls *must* add up to the total_length
- * given to png_write_chunk_start().
+ * given to png_write_chunk_header().
  */
 void PNGAPI
-png_write_chunk_data(png_structp png_ptr, png_bytep data, png_size_t length)
+png_write_chunk_data(png_structp png_ptr, png_const_bytep data,
+    png_size_t length)
 {
    /* Write the data, and run the CRC over it */
    if (png_ptr == NULL)
       return;
+
    if (data != NULL && length > 0)
    {
       png_write_data(png_ptr, data, length);
+
       /* Update the CRC after writing the data,
        * in case that the user I/O routine alters it.
        */
@@ -160,7 +159,7 @@ png_write_chunk_data(png_structp png_ptr, png_bytep data, png_size_t length)
    }
 }
 
-/* Finish a chunk started with png_write_chunk_start(). */
+/* Finish a chunk started with png_write_chunk_header(). */
 void PNGAPI
 png_write_chunk_end(png_structp png_ptr)
 {
@@ -181,7 +180,183 @@ png_write_chunk_end(png_structp png_ptr)
    png_write_data(png_ptr, buf, (png_size_t)4);
 }
 
-#if defined(PNG_WRITE_TEXT_SUPPORTED) || defined(PNG_WRITE_iCCP_SUPPORTED)
+/* Write a PNG chunk all at once.  The type is an array of ASCII characters
+ * representing the chunk name.  The array must be at least 4 bytes in
+ * length, and does not need to be null terminated.  To be safe, pass the
+ * pre-defined chunk names here, and if you need a new one, define it
+ * where the others are defined.  The length is the length of the data.
+ * All the data must be present.  If that is not possible, use the
+ * png_write_chunk_start(), png_write_chunk_data(), and png_write_chunk_end()
+ * functions instead.
+ */
+static void
+png_write_complete_chunk(png_structp png_ptr, png_uint_32 chunk_name,
+   png_const_bytep data, png_size_t length)
+{
+   if (png_ptr == NULL)
+      return;
+
+   /* On 64 bit architectures 'length' may not fit in a png_uint_32. */
+   if (length > PNG_UINT_32_MAX)
+      png_error(png_ptr, "length exceeds PNG maxima");
+
+   png_write_chunk_header(png_ptr, chunk_name, (png_uint_32)length);
+   png_write_chunk_data(png_ptr, data, length);
+   png_write_chunk_end(png_ptr);
+}
+
+/* This is the API that calls the internal function above. */
+void PNGAPI
+png_write_chunk(png_structp png_ptr, png_const_bytep chunk_string,
+   png_const_bytep data, png_size_t length)
+{
+   png_write_complete_chunk(png_ptr, PNG_CHUNK_FROM_STRING(chunk_string), data,
+      length);
+}
+
+/* Initialize the compressor for the appropriate type of compression. */
+static void
+png_zlib_claim(png_structp png_ptr, png_uint_32 state)
+{
+   if (!(png_ptr->zlib_state & PNG_ZLIB_IN_USE))
+   {
+      /* If already initialized for 'state' do not re-init. */
+      if (png_ptr->zlib_state != state)
+      {
+         int ret = Z_OK;
+         png_const_charp who = "-";
+
+         /* If actually initialized for another state do a deflateEnd. */
+         if (png_ptr->zlib_state != PNG_ZLIB_UNINITIALIZED)
+         {
+            ret = deflateEnd(&png_ptr->zstream);
+            who = "end";
+            png_ptr->zlib_state = PNG_ZLIB_UNINITIALIZED;
+         }
+
+         /* zlib itself detects an incomplete state on deflateEnd */
+         if (ret == Z_OK) switch (state)
+         {
+#           ifdef PNG_WRITE_COMPRESSED_TEXT_SUPPORTED
+               case PNG_ZLIB_FOR_TEXT:
+                  ret = deflateInit2(&png_ptr->zstream,
+                     png_ptr->zlib_text_level, png_ptr->zlib_text_method,
+                     png_ptr->zlib_text_window_bits,
+                     png_ptr->zlib_text_mem_level, png_ptr->zlib_text_strategy);
+                  who = "text";
+                  break;
+#           endif
+
+            case PNG_ZLIB_FOR_IDAT:
+               ret = deflateInit2(&png_ptr->zstream, png_ptr->zlib_level,
+                   png_ptr->zlib_method, png_ptr->zlib_window_bits,
+                   png_ptr->zlib_mem_level, png_ptr->zlib_strategy);
+               who = "IDAT";
+               break;
+
+            default:
+               png_error(png_ptr, "invalid zlib state");
+         }
+
+         if (ret == Z_OK)
+            png_ptr->zlib_state = state;
+
+         else /* an error in deflateEnd or deflateInit2 */
+         {
+            size_t pos = 0;
+            char msg[64];
+
+            pos = png_safecat(msg, sizeof msg, pos,
+               "zlib failed to initialize compressor (");
+            pos = png_safecat(msg, sizeof msg, pos, who);
+
+            switch (ret)
+            {
+               case Z_VERSION_ERROR:
+                  pos = png_safecat(msg, sizeof msg, pos, ") version error");
+                  break;
+
+               case Z_STREAM_ERROR:
+                  pos = png_safecat(msg, sizeof msg, pos, ") stream error");
+                  break;
+
+               case Z_MEM_ERROR:
+                  pos = png_safecat(msg, sizeof msg, pos, ") memory error");
+                  break;
+
+               default:
+                  pos = png_safecat(msg, sizeof msg, pos, ") unknown error");
+                  break;
+            }
+
+            png_error(png_ptr, msg);
+         }
+      }
+
+      /* Here on success, claim the zstream: */
+      png_ptr->zlib_state |= PNG_ZLIB_IN_USE;
+   }
+
+   else
+      png_error(png_ptr, "zstream already in use (internal error)");
+}
+
+/* The opposite: release the stream.  It is also reset, this API will warn on
+ * error but will not fail.
+ */
+static void
+png_zlib_release(png_structp png_ptr)
+{
+   if (png_ptr->zlib_state & PNG_ZLIB_IN_USE)
+   {
+      int ret = deflateReset(&png_ptr->zstream);
+
+      png_ptr->zlib_state &= ~PNG_ZLIB_IN_USE;
+
+      if (ret != Z_OK)
+      {
+         png_const_charp err;
+         PNG_WARNING_PARAMETERS(p)
+
+         switch (ret)
+         {
+            case Z_VERSION_ERROR:
+               err = "version";
+               break;
+
+            case Z_STREAM_ERROR:
+               err = "stream";
+               break;
+
+            case Z_MEM_ERROR:
+               err = "memory";
+               break;
+
+            default:
+               err = "unknown";
+               break;
+         }
+
+         png_warning_parameter_signed(p, 1, PNG_NUMBER_FORMAT_d, ret);
+         png_warning_parameter(p, 2, err);
+
+         if (png_ptr->zstream.msg)
+            err = png_ptr->zstream.msg;
+         else
+            err = "[no zlib message]";
+
+         png_warning_parameter(p, 3, err);
+
+         png_formatted_warning(png_ptr, p,
+            "zlib failed to reset compressor: @1(@2): @3");
+      }
+   }
+
+   else
+      png_warning(png_ptr, "zstream not in use (internal error)");
+}
+
+#ifdef PNG_WRITE_COMPRESSED_TEXT_SUPPORTED
 /* This pair of functions encapsulates the operation of (a) compressing a
  * text string, and (b) issuing it later as a series of chunk data writes.
  * The compression_state structure is shared context for these functions
@@ -190,18 +365,18 @@ png_write_chunk_end(png_structp png_ptr)
 
 typedef struct
 {
-   char *input;   /* The uncompressed input data */
-   int input_len;   /* Its length */
-   int num_output_ptr; /* Number of output pointers used */
-   int max_output_ptr; /* Size of output_ptr */
-   png_charpp output_ptr; /* Array of pointers to output */
+   png_const_bytep input;   /* The uncompressed input data */
+   png_size_t input_len;    /* Its length */
+   int num_output_ptr;      /* Number of output pointers used */
+   int max_output_ptr;      /* Size of output_ptr */
+   png_bytep *output_ptr;   /* Array of pointers to output */
 } compression_state;
 
 /* Compress given text into storage in the png_ptr structure */
 static int /* PRIVATE */
 png_text_compress(png_structp png_ptr,
-        png_charp text, png_size_t text_len, int compression,
-        compression_state *comp)
+    png_const_charp text, png_size_t text_len, int compression,
+    compression_state *comp)
 {
    int ret;
 
@@ -209,25 +384,22 @@ png_text_compress(png_structp png_ptr,
    comp->max_output_ptr = 0;
    comp->output_ptr = NULL;
    comp->input = NULL;
-   comp->input_len = 0;
+   comp->input_len = text_len;
 
    /* We may just want to pass the text right through */
    if (compression == PNG_TEXT_COMPRESSION_NONE)
    {
-       comp->input = text;
-       comp->input_len = text_len;
-       return((int)text_len);
+      comp->input = (png_const_bytep)text;
+      return((int)text_len);
    }
 
    if (compression >= PNG_TEXT_COMPRESSION_LAST)
    {
-#ifdef PNG_STDIO_SUPPORTED
-      char msg[50];
-      png_snprintf(msg, 50, "Unknown compression type %d", compression);
-      png_warning(png_ptr, msg);
-#else
-      png_warning(png_ptr, "Unknown compression type");
-#endif
+      PNG_WARNING_PARAMETERS(p)
+
+      png_warning_parameter_signed(p, 1, PNG_NUMBER_FORMAT_d,
+         compression);
+      png_formatted_warning(png_ptr, p, "Unknown compression type @1");
    }
 
    /* We can't write the chunk until we find out how much data we have,
@@ -244,26 +416,33 @@ png_text_compress(png_structp png_ptr,
     * data, or if the input string is incredibly large (although this
     * wouldn't cause a failure, just a slowdown due to swapping).
     */
+   png_zlib_claim(png_ptr, PNG_ZLIB_FOR_TEXT);
 
    /* Set up the compression buffers */
+   /* TODO: the following cast hides a potential overflow problem. */
    png_ptr->zstream.avail_in = (uInt)text_len;
+
+   /* NOTE: assume zlib doesn't overwrite the input */
    png_ptr->zstream.next_in = (Bytef *)text;
-   png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
-   png_ptr->zstream.next_out = (Bytef *)png_ptr->zbuf;
+   png_ptr->zstream.avail_out = png_ptr->zbuf_size;
+   png_ptr->zstream.next_out = png_ptr->zbuf;
 
    /* This is the same compression loop as in png_write_row() */
    do
    {
       /* Compress the data */
       ret = deflate(&png_ptr->zstream, Z_NO_FLUSH);
+
       if (ret != Z_OK)
       {
          /* Error */
          if (png_ptr->zstream.msg != NULL)
             png_error(png_ptr, png_ptr->zstream.msg);
+
          else
             png_error(png_ptr, "zlib error");
       }
+
       /* Check to see if we need more room */
       if (!(png_ptr->zstream.avail_out))
       {
@@ -276,28 +455,33 @@ png_text_compress(png_structp png_ptr,
             comp->max_output_ptr = comp->num_output_ptr + 4;
             if (comp->output_ptr != NULL)
             {
-               png_charpp old_ptr;
+               png_bytepp old_ptr;
 
                old_ptr = comp->output_ptr;
-               comp->output_ptr = (png_charpp)png_malloc(png_ptr,
-                  (png_alloc_size_t)
-                  (comp->max_output_ptr * png_sizeof(png_charpp)));
+
+               comp->output_ptr = (png_bytepp)png_malloc(png_ptr,
+                   (png_alloc_size_t)
+                   (comp->max_output_ptr * png_sizeof(png_charpp)));
+
                png_memcpy(comp->output_ptr, old_ptr, old_max
-                  * png_sizeof(png_charp));
+                   * png_sizeof(png_charp));
+
                png_free(png_ptr, old_ptr);
             }
             else
-               comp->output_ptr = (png_charpp)png_malloc(png_ptr,
-                  (png_alloc_size_t)
-                  (comp->max_output_ptr * png_sizeof(png_charp)));
+               comp->output_ptr = (png_bytepp)png_malloc(png_ptr,
+                   (png_alloc_size_t)
+                   (comp->max_output_ptr * png_sizeof(png_charp)));
          }
 
          /* Save the data */
          comp->output_ptr[comp->num_output_ptr] =
-            (png_charp)png_malloc(png_ptr,
-            (png_alloc_size_t)png_ptr->zbuf_size);
+             (png_bytep)png_malloc(png_ptr,
+             (png_alloc_size_t)png_ptr->zbuf_size);
+
          png_memcpy(comp->output_ptr[comp->num_output_ptr], png_ptr->zbuf,
-            png_ptr->zbuf_size);
+             png_ptr->zbuf_size);
+
          comp->num_output_ptr++;
 
          /* and reset the buffer */
@@ -327,29 +511,35 @@ png_text_compress(png_structp png_ptr,
                comp->max_output_ptr = comp->num_output_ptr + 4;
                if (comp->output_ptr != NULL)
                {
-                  png_charpp old_ptr;
+                  png_bytepp old_ptr;
 
                   old_ptr = comp->output_ptr;
+
                   /* This could be optimized to realloc() */
-                  comp->output_ptr = (png_charpp)png_malloc(png_ptr,
-                     (png_alloc_size_t)(comp->max_output_ptr *
-                     png_sizeof(png_charp)));
+                  comp->output_ptr = (png_bytepp)png_malloc(png_ptr,
+                      (png_alloc_size_t)(comp->max_output_ptr *
+                      png_sizeof(png_charp)));
+
                   png_memcpy(comp->output_ptr, old_ptr,
-                     old_max * png_sizeof(png_charp));
+                      old_max * png_sizeof(png_charp));
+
                   png_free(png_ptr, old_ptr);
                }
+
                else
-                  comp->output_ptr = (png_charpp)png_malloc(png_ptr,
-                     (png_alloc_size_t)(comp->max_output_ptr *
-                     png_sizeof(png_charp)));
+                  comp->output_ptr = (png_bytepp)png_malloc(png_ptr,
+                      (png_alloc_size_t)(comp->max_output_ptr *
+                      png_sizeof(png_charp)));
             }
 
             /* Save the data */
             comp->output_ptr[comp->num_output_ptr] =
-               (png_charp)png_malloc(png_ptr,
-               (png_alloc_size_t)png_ptr->zbuf_size);
+                (png_bytep)png_malloc(png_ptr,
+                (png_alloc_size_t)png_ptr->zbuf_size);
+
             png_memcpy(comp->output_ptr[comp->num_output_ptr], png_ptr->zbuf,
-               png_ptr->zbuf_size);
+                png_ptr->zbuf_size);
+
             comp->num_output_ptr++;
 
             /* and reset the buffer pointers */
@@ -362,6 +552,7 @@ png_text_compress(png_structp png_ptr,
          /* We got an error */
          if (png_ptr->zstream.msg != NULL)
             png_error(png_ptr, png_ptr->zstream.msg);
+
          else
             png_error(png_ptr, "zlib error");
       }
@@ -369,6 +560,7 @@ png_text_compress(png_structp png_ptr,
 
    /* Text length is number of buffers plus last buffer */
    text_len = png_ptr->zbuf_size * comp->num_output_ptr;
+
    if (png_ptr->zstream.avail_out < png_ptr->zbuf_size)
       text_len += png_ptr->zbuf_size - (png_size_t)png_ptr->zstream.avail_out;
 
@@ -384,30 +576,97 @@ png_write_compressed_data_out(png_structp png_ptr, compression_state *comp)
    /* Handle the no-compression case */
    if (comp->input)
    {
-      png_write_chunk_data(png_ptr, (png_bytep)comp->input,
-                            (png_size_t)comp->input_len);
+      png_write_chunk_data(png_ptr, comp->input, comp->input_len);
+
       return;
    }
 
+#ifdef PNG_WRITE_OPTIMIZE_CMF_SUPPORTED
+   /* The zbuf_size test is because the code below doesn't work if zbuf_size is
+    * '1'; simply skip it to avoid memory overwrite.
+    */
+   if (comp->input_len >= 2 && comp->input_len < 16384 && png_ptr->zbuf_size > 1)
+   {
+      unsigned int z_cmf;  /* zlib compression method and flags */
+
+      /* Optimize the CMF field in the zlib stream.  This hack of the zlib
+       * stream is compliant to the stream specification.
+       */
+
+      if (comp->num_output_ptr)
+        z_cmf = comp->output_ptr[0][0];
+      else
+        z_cmf = png_ptr->zbuf[0];
+
+      if ((z_cmf & 0x0f) == 8 && (z_cmf & 0xf0) <= 0x70)
+      {
+         unsigned int z_cinfo;
+         unsigned int half_z_window_size;
+         png_size_t uncompressed_text_size = comp->input_len;
+
+         z_cinfo = z_cmf >> 4;
+         half_z_window_size = 1 << (z_cinfo + 7);
+
+         while (uncompressed_text_size <= half_z_window_size &&
+             half_z_window_size >= 256)
+         {
+            z_cinfo--;
+            half_z_window_size >>= 1;
+         }
+
+         z_cmf = (z_cmf & 0x0f) | (z_cinfo << 4);
+
+         if (comp->num_output_ptr)
+         {
+
+           if (comp->output_ptr[0][0] != z_cmf)
+           {
+              int tmp;
+
+              comp->output_ptr[0][0] = (png_byte)z_cmf;
+              tmp = comp->output_ptr[0][1] & 0xe0;
+              tmp += 0x1f - ((z_cmf << 8) + tmp) % 0x1f;
+              comp->output_ptr[0][1] = (png_byte)tmp;
+           }
+         }
+         else
+         {
+            int tmp;
+
+            png_ptr->zbuf[0] = (png_byte)z_cmf;
+            tmp = png_ptr->zbuf[1] & 0xe0;
+            tmp += 0x1f - ((z_cmf << 8) + tmp) % 0x1f;
+            png_ptr->zbuf[1] = (png_byte)tmp;
+         }
+      }
+
+      else
+         png_error(png_ptr,
+             "Invalid zlib compression method or flags in non-IDAT chunk");
+   }
+#endif /* PNG_WRITE_OPTIMIZE_CMF_SUPPORTED */
+
    /* Write saved output buffers, if any */
    for (i = 0; i < comp->num_output_ptr; i++)
    {
-      png_write_chunk_data(png_ptr, (png_bytep)comp->output_ptr[i],
-         (png_size_t)png_ptr->zbuf_size);
+      png_write_chunk_data(png_ptr, comp->output_ptr[i],
+          (png_size_t)png_ptr->zbuf_size);
+
       png_free(png_ptr, comp->output_ptr[i]);
    }
+
    if (comp->max_output_ptr != 0)
       png_free(png_ptr, comp->output_ptr);
+
    /* Write anything left in zbuf */
    if (png_ptr->zstream.avail_out < (png_uint_32)png_ptr->zbuf_size)
       png_write_chunk_data(png_ptr, png_ptr->zbuf,
-         (png_size_t)(png_ptr->zbuf_size - png_ptr->zstream.avail_out));
+          (png_size_t)(png_ptr->zbuf_size - png_ptr->zstream.avail_out));
 
    /* Reset zlib for another zTXt/iTXt or image data */
-   deflateReset(&png_ptr->zstream);
-   png_ptr->zstream.data_type = Z_BINARY;
+   png_zlib_release(png_ptr);
 }
-#endif
+#endif /* PNG_WRITE_COMPRESSED_TEXT_SUPPORTED */
 
 /* Write the IHDR chunk, and update the png_struct with the necessary
  * information.  Note that the rest of this code depends upon this
@@ -415,12 +674,9 @@ png_write_compressed_data_out(png_structp png_ptr, compression_state *comp)
  */
 void /* PRIVATE */
 png_write_IHDR(png_structp png_ptr, png_uint_32 width, png_uint_32 height,
-   int bit_depth, int color_type, int compression_type, int filter_type,
-   int interlace_type)
+    int bit_depth, int color_type, int compression_type, int filter_type,
+    int interlace_type)
 {
-   PNG_IHDR;
-   int ret;
-
    png_byte buf[13]; /* Buffer to store the IHDR info */
 
    png_debug(1, "in png_write_IHDR");
@@ -435,36 +691,61 @@ png_write_IHDR(png_structp png_ptr, png_uint_32 width, png_uint_32 height,
             case 2:
             case 4:
             case 8:
-            case 16: png_ptr->channels = 1; break;
-            default: png_error(png_ptr,
-                         "Invalid bit depth for grayscale image");
+#ifdef PNG_WRITE_16BIT_SUPPORTED
+            case 16:
+#endif
+               png_ptr->channels = 1; break;
+
+            default:
+               png_error(png_ptr,
+                   "Invalid bit depth for grayscale image");
          }
          break;
+
       case PNG_COLOR_TYPE_RGB:
+#ifdef PNG_WRITE_16BIT_SUPPORTED
          if (bit_depth != 8 && bit_depth != 16)
+#else
+         if (bit_depth != 8)
+#endif
             png_error(png_ptr, "Invalid bit depth for RGB image");
+
          png_ptr->channels = 3;
          break;
+
       case PNG_COLOR_TYPE_PALETTE:
          switch (bit_depth)
          {
             case 1:
             case 2:
             case 4:
-            case 8: png_ptr->channels = 1; break;
-            default: png_error(png_ptr, "Invalid bit depth for paletted image");
+            case 8:
+               png_ptr->channels = 1;
+               break;
+
+            default:
+               png_error(png_ptr, "Invalid bit depth for paletted image");
          }
          break;
+
       case PNG_COLOR_TYPE_GRAY_ALPHA:
          if (bit_depth != 8 && bit_depth != 16)
             png_error(png_ptr, "Invalid bit depth for grayscale+alpha image");
+
          png_ptr->channels = 2;
          break;
+
       case PNG_COLOR_TYPE_RGB_ALPHA:
+#ifdef PNG_WRITE_16BIT_SUPPORTED
          if (bit_depth != 8 && bit_depth != 16)
+#else
+         if (bit_depth != 8)
+#endif
             png_error(png_ptr, "Invalid bit depth for RGBA image");
+
          png_ptr->channels = 4;
          break;
+
       default:
          png_error(png_ptr, "Invalid image color type specified");
    }
@@ -486,13 +767,13 @@ png_write_IHDR(png_structp png_ptr, png_uint_32 width, png_uint_32 height,
     */
    if (
 #ifdef PNG_MNG_FEATURES_SUPPORTED
-      !((png_ptr->mng_features_permitted & PNG_FLAG_MNG_FILTER_64) &&
-      ((png_ptr->mode&PNG_HAVE_PNG_SIGNATURE) == 0) &&
-      (color_type == PNG_COLOR_TYPE_RGB ||
-       color_type == PNG_COLOR_TYPE_RGB_ALPHA) &&
-      (filter_type == PNG_INTRAPIXEL_DIFFERENCING)) &&
+       !((png_ptr->mng_features_permitted & PNG_FLAG_MNG_FILTER_64) &&
+       ((png_ptr->mode&PNG_HAVE_PNG_SIGNATURE) == 0) &&
+       (color_type == PNG_COLOR_TYPE_RGB ||
+        color_type == PNG_COLOR_TYPE_RGB_ALPHA) &&
+       (filter_type == PNG_INTRAPIXEL_DIFFERENCING)) &&
 #endif
-      filter_type != PNG_FILTER_TYPE_BASE)
+       filter_type != PNG_FILTER_TYPE_BASE)
    {
       png_warning(png_ptr, "Invalid filter type specified");
       filter_type = PNG_FILTER_TYPE_BASE;
@@ -500,7 +781,7 @@ png_write_IHDR(png_structp png_ptr, png_uint_32 width, png_uint_32 height,
 
 #ifdef PNG_WRITE_INTERLACING_SUPPORTED
    if (interlace_type != PNG_INTERLACE_NONE &&
-      interlace_type != PNG_INTERLACE_ADAM7)
+       interlace_type != PNG_INTERLACE_ADAM7)
    {
       png_warning(png_ptr, "Invalid interlace type specified");
       interlace_type = PNG_INTERLACE_ADAM7;
@@ -537,55 +818,73 @@ png_write_IHDR(png_structp png_ptr, png_uint_32 width, png_uint_32 height,
    buf[12] = (png_byte)interlace_type;
 
    /* Write the chunk */
-   png_write_chunk(png_ptr, (png_bytep)png_IHDR, buf, (png_size_t)13);
+   png_write_complete_chunk(png_ptr, png_IHDR, buf, (png_size_t)13);
 
    /* Initialize zlib with PNG info */
    png_ptr->zstream.zalloc = png_zalloc;
    png_ptr->zstream.zfree = png_zfree;
    png_ptr->zstream.opaque = (voidpf)png_ptr;
+
    if (!(png_ptr->do_filter))
    {
       if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE ||
-         png_ptr->bit_depth < 8)
+          png_ptr->bit_depth < 8)
          png_ptr->do_filter = PNG_FILTER_NONE;
+
       else
          png_ptr->do_filter = PNG_ALL_FILTERS;
    }
+
    if (!(png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_STRATEGY))
    {
       if (png_ptr->do_filter != PNG_FILTER_NONE)
          png_ptr->zlib_strategy = Z_FILTERED;
+
       else
          png_ptr->zlib_strategy = Z_DEFAULT_STRATEGY;
    }
+
    if (!(png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_LEVEL))
       png_ptr->zlib_level = Z_DEFAULT_COMPRESSION;
+
    if (!(png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_MEM_LEVEL))
       png_ptr->zlib_mem_level = 8;
+
    if (!(png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_WINDOW_BITS))
       png_ptr->zlib_window_bits = 15;
+
    if (!(png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_METHOD))
       png_ptr->zlib_method = 8;
-   ret = deflateInit2(&png_ptr->zstream, png_ptr->zlib_level,
-         png_ptr->zlib_method, png_ptr->zlib_window_bits,
-         png_ptr->zlib_mem_level, png_ptr->zlib_strategy);
-   if (ret != Z_OK)
-   {
-      if (ret == Z_VERSION_ERROR) png_error(png_ptr,
-          "zlib failed to initialize compressor -- version error");
-      if (ret == Z_STREAM_ERROR) png_error(png_ptr,
-           "zlib failed to initialize compressor -- stream error");
-      if (ret == Z_MEM_ERROR) png_error(png_ptr,
-           "zlib failed to initialize compressor -- mem error");
-      png_error(png_ptr, "zlib failed to initialize compressor");
-   }
-   png_ptr->zstream.next_out = png_ptr->zbuf;
-   png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
-   /* libpng is not interested in zstream.data_type */
-   /* Set it to a predefined value, to avoid its evaluation inside zlib */
-   png_ptr->zstream.data_type = Z_BINARY;
 
-   png_ptr->mode = PNG_HAVE_IHDR;
+#ifdef PNG_WRITE_COMPRESSED_TEXT_SUPPORTED
+#ifdef PNG_WRITE_CUSTOMIZE_ZTXT_COMPRESSION_SUPPORTED
+   if (!(png_ptr->flags & PNG_FLAG_ZTXT_CUSTOM_STRATEGY))
+      png_ptr->zlib_text_strategy = Z_DEFAULT_STRATEGY;
+
+   if (!(png_ptr->flags & PNG_FLAG_ZTXT_CUSTOM_LEVEL))
+      png_ptr->zlib_text_level = png_ptr->zlib_level;
+
+   if (!(png_ptr->flags & PNG_FLAG_ZTXT_CUSTOM_MEM_LEVEL))
+      png_ptr->zlib_text_mem_level = png_ptr->zlib_mem_level;
+
+   if (!(png_ptr->flags & PNG_FLAG_ZTXT_CUSTOM_WINDOW_BITS))
+      png_ptr->zlib_text_window_bits = png_ptr->zlib_window_bits;
+
+   if (!(png_ptr->flags & PNG_FLAG_ZTXT_CUSTOM_METHOD))
+      png_ptr->zlib_text_method = png_ptr->zlib_method;
+#else
+   png_ptr->zlib_text_strategy = Z_DEFAULT_STRATEGY;
+   png_ptr->zlib_text_level = png_ptr->zlib_level;
+   png_ptr->zlib_text_mem_level = png_ptr->zlib_mem_level;
+   png_ptr->zlib_text_window_bits = png_ptr->zlib_window_bits;
+   png_ptr->zlib_text_method = png_ptr->zlib_method;
+#endif /* PNG_WRITE_CUSTOMIZE_ZTXT_COMPRESSION_SUPPORTED */
+#endif /* PNG_WRITE_COMPRESSED_TEXT_SUPPORTED */
+
+   /* Record that the compressor has not yet been initialized. */
+   png_ptr->zlib_state = PNG_ZLIB_UNINITIALIZED;
+
+   png_ptr->mode = PNG_HAVE_IHDR; /* not READY_FOR_ZTXT */
 }
 
 /* Write the palette.  We are careful not to trust png_color to be in the
@@ -593,45 +892,47 @@ png_write_IHDR(png_structp png_ptr, png_uint_32 width, png_uint_32 height,
  * structure.
  */
 void /* PRIVATE */
-png_write_PLTE(png_structp png_ptr, png_colorp palette, png_uint_32 num_pal)
+png_write_PLTE(png_structp png_ptr, png_const_colorp palette,
+    png_uint_32 num_pal)
 {
-   PNG_PLTE;
    png_uint_32 i;
-   png_colorp pal_ptr;
+   png_const_colorp pal_ptr;
    png_byte buf[3];
 
    png_debug(1, "in png_write_PLTE");
 
    if ((
 #ifdef PNG_MNG_FEATURES_SUPPORTED
-        !(png_ptr->mng_features_permitted & PNG_FLAG_MNG_EMPTY_PLTE) &&
+       !(png_ptr->mng_features_permitted & PNG_FLAG_MNG_EMPTY_PLTE) &&
 #endif
-        num_pal == 0) || num_pal > 256)
+       num_pal == 0) || num_pal > 256)
    {
-     if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
-     {
-        png_error(png_ptr, "Invalid number of colors in palette");
-     }
-     else
-     {
-        png_warning(png_ptr, "Invalid number of colors in palette");
-        return;
-     }
+      if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
+      {
+         png_error(png_ptr, "Invalid number of colors in palette");
+      }
+
+      else
+      {
+         png_warning(png_ptr, "Invalid number of colors in palette");
+         return;
+      }
    }
 
    if (!(png_ptr->color_type&PNG_COLOR_MASK_COLOR))
    {
       png_warning(png_ptr,
-        "Ignoring request to write a PLTE chunk in grayscale PNG");
+          "Ignoring request to write a PLTE chunk in grayscale PNG");
+
       return;
    }
 
    png_ptr->num_palette = (png_uint_16)num_pal;
    png_debug1(3, "num_palette = %d", png_ptr->num_palette);
 
-   png_write_chunk_start(png_ptr, (png_bytep)png_PLTE,
-     (png_uint_32)(num_pal * 3));
+   png_write_chunk_header(png_ptr, png_PLTE, (png_uint_32)(num_pal * 3));
 #ifdef PNG_POINTER_INDEXING_SUPPORTED
+
    for (i = 0, pal_ptr = palette; i < num_pal; i++, pal_ptr++)
    {
       buf[0] = pal_ptr->red;
@@ -639,11 +940,13 @@ png_write_PLTE(png_structp png_ptr, png_colorp palette, png_uint_32 num_pal)
       buf[2] = pal_ptr->blue;
       png_write_chunk_data(png_ptr, buf, (png_size_t)3);
    }
+
 #else
    /* This is a little slower but some buggy compilers need to do this
     * instead
     */
    pal_ptr=palette;
+
    for (i = 0; i < num_pal; i++)
    {
       buf[0] = pal_ptr[i].red;
@@ -651,6 +954,7 @@ png_write_PLTE(png_structp png_ptr, png_colorp palette, png_uint_32 num_pal)
       buf[2] = pal_ptr[i].blue;
       png_write_chunk_data(png_ptr, buf, (png_size_t)3);
    }
+
 #endif
    png_write_chunk_end(png_ptr);
    png_ptr->mode |= PNG_HAVE_PLTE;
@@ -660,16 +964,17 @@ png_write_PLTE(png_structp png_ptr, png_colorp palette, png_uint_32 num_pal)
 void /* PRIVATE */
 png_write_IDAT(png_structp png_ptr, png_bytep data, png_size_t length)
 {
-   PNG_IDAT;
-
    png_debug(1, "in png_write_IDAT");
 
-   /* Optimize the CMF field in the zlib stream. */
-   /* This hack of the zlib stream is compliant to the stream specification. */
+#ifdef PNG_WRITE_OPTIMIZE_CMF_SUPPORTED
    if (!(png_ptr->mode & PNG_HAVE_IDAT) &&
        png_ptr->compression_type == PNG_COMPRESSION_TYPE_BASE)
    {
+      /* Optimize the CMF field in the zlib stream.  This hack of the zlib
+       * stream is compliant to the stream specification.
+       */
       unsigned int z_cmf = data[0];  /* zlib compression method and flags */
+
       if ((z_cmf & 0x0f) == 8 && (z_cmf & 0xf0) <= 0x70)
       {
          /* Avoid memory underflows and multiplication overflows.
@@ -680,107 +985,115 @@ png_write_IDAT(png_structp png_ptr, png_bytep data, png_size_t length)
          if (length >= 2 &&
              png_ptr->height < 16384 && png_ptr->width < 16384)
          {
+            /* Compute the maximum possible length of the datastream */
+
+            /* Number of pixels, plus for each row a filter byte
+             * and possibly a padding byte, so increase the maximum
+             * size to account for these.
+             */
+            unsigned int z_cinfo;
+            unsigned int half_z_window_size;
             png_uint_32 uncompressed_idat_size = png_ptr->height *
-               ((png_ptr->width *
-               png_ptr->channels * png_ptr->bit_depth + 15) >> 3);
-            unsigned int z_cinfo = z_cmf >> 4;
-            unsigned int half_z_window_size = 1 << (z_cinfo + 7);
+                ((png_ptr->width *
+                png_ptr->channels * png_ptr->bit_depth + 15) >> 3);
+
+            /* If it's interlaced, each block of 8 rows is sent as up to
+             * 14 rows, i.e., 6 additional rows, each with a filter byte
+             * and possibly a padding byte
+             */
+            if (png_ptr->interlaced)
+               uncompressed_idat_size += ((png_ptr->height + 7)/8) *
+                   (png_ptr->bit_depth < 8 ? 12 : 6);
+
+            z_cinfo = z_cmf >> 4;
+            half_z_window_size = 1 << (z_cinfo + 7);
+
             while (uncompressed_idat_size <= half_z_window_size &&
-                   half_z_window_size >= 256)
+                half_z_window_size >= 256)
             {
                z_cinfo--;
                half_z_window_size >>= 1;
             }
+
             z_cmf = (z_cmf & 0x0f) | (z_cinfo << 4);
-            if (data[0] != (png_byte)z_cmf)
+
+            if (data[0] != z_cmf)
             {
+               int tmp;
                data[0] = (png_byte)z_cmf;
-               data[1] &= 0xe0;
-               data[1] += (png_byte)(0x1f - ((z_cmf << 8) + data[1]) % 0x1f);
+               tmp = data[1] & 0xe0;
+               tmp += 0x1f - ((z_cmf << 8) + tmp) % 0x1f;
+               data[1] = (png_byte)tmp;
             }
          }
       }
+
       else
          png_error(png_ptr,
-            "Invalid zlib compression method or flags in IDAT");
+             "Invalid zlib compression method or flags in IDAT");
    }
+#endif /* PNG_WRITE_OPTIMIZE_CMF_SUPPORTED */
 
-   png_write_chunk(png_ptr, (png_bytep)png_IDAT, data, length);
+   png_write_complete_chunk(png_ptr, png_IDAT, data, length);
    png_ptr->mode |= PNG_HAVE_IDAT;
+
+   /* Prior to 1.5.4 this code was replicated in every caller (except at the
+    * end, where it isn't technically necessary).  Since this function has
+    * flushed the data we can safely reset the zlib output buffer here.
+    */
+   png_ptr->zstream.next_out = png_ptr->zbuf;
+   png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
 }
 
 /* Write an IEND chunk */
 void /* PRIVATE */
 png_write_IEND(png_structp png_ptr)
 {
-   PNG_IEND;
-
    png_debug(1, "in png_write_IEND");
 
-   png_write_chunk(png_ptr, (png_bytep)png_IEND, NULL,
-     (png_size_t)0);
+   png_write_complete_chunk(png_ptr, png_IEND, NULL, (png_size_t)0);
    png_ptr->mode |= PNG_HAVE_IEND;
 }
 
 #ifdef PNG_WRITE_gAMA_SUPPORTED
 /* Write a gAMA chunk */
-#ifdef PNG_FLOATING_POINT_SUPPORTED
-void /* PRIVATE */
-png_write_gAMA(png_structp png_ptr, double file_gamma)
-{
-   PNG_gAMA;
-   png_uint_32 igamma;
-   png_byte buf[4];
-
-   png_debug(1, "in png_write_gAMA");
-
-   /* file_gamma is saved in 1/100,000ths */
-   igamma = (png_uint_32)(file_gamma * 100000.0 + 0.5);
-   png_save_uint_32(buf, igamma);
-   png_write_chunk(png_ptr, (png_bytep)png_gAMA, buf, (png_size_t)4);
-}
-#endif
-#ifdef PNG_FIXED_POINT_SUPPORTED
 void /* PRIVATE */
 png_write_gAMA_fixed(png_structp png_ptr, png_fixed_point file_gamma)
 {
-   PNG_gAMA;
    png_byte buf[4];
 
    png_debug(1, "in png_write_gAMA");
 
    /* file_gamma is saved in 1/100,000ths */
    png_save_uint_32(buf, (png_uint_32)file_gamma);
-   png_write_chunk(png_ptr, (png_bytep)png_gAMA, buf, (png_size_t)4);
+   png_write_complete_chunk(png_ptr, png_gAMA, buf, (png_size_t)4);
 }
 #endif
-#endif
 
 #ifdef PNG_WRITE_sRGB_SUPPORTED
 /* Write a sRGB chunk */
 void /* PRIVATE */
 png_write_sRGB(png_structp png_ptr, int srgb_intent)
 {
-   PNG_sRGB;
    png_byte buf[1];
 
    png_debug(1, "in png_write_sRGB");
 
    if (srgb_intent >= PNG_sRGB_INTENT_LAST)
-         png_warning(png_ptr,
-            "Invalid sRGB rendering intent specified");
+      png_warning(png_ptr,
+          "Invalid sRGB rendering intent specified");
+
    buf[0]=(png_byte)srgb_intent;
-   png_write_chunk(png_ptr, (png_bytep)png_sRGB, buf, (png_size_t)1);
+   png_write_complete_chunk(png_ptr, png_sRGB, buf, (png_size_t)1);
 }
 #endif
 
 #ifdef PNG_WRITE_iCCP_SUPPORTED
 /* Write an iCCP chunk */
 void /* PRIVATE */
-png_write_iCCP(png_structp png_ptr, png_charp name, int compression_type,
-   png_charp profile, int profile_len)
+png_write_iCCP(png_structp png_ptr, png_const_charp name, int compression_type,
+    png_const_charp profile, int profile_len)
 {
-   PNG_iCCP;
    png_size_t name_len;
    png_charp new_name;
    compression_state comp;
@@ -794,8 +1107,7 @@ png_write_iCCP(png_structp png_ptr, png_charp name, int compression_type,
    comp.input = NULL;
    comp.input_len = 0;
 
-   if ((name_len = png_check_keyword(png_ptr, name,
-      &new_name)) == 0)
+   if ((name_len = png_check_keyword(png_ptr, name, &new_name)) == 0)
       return;
 
    if (compression_type != PNG_COMPRESSION_TYPE_BASE)
@@ -806,15 +1118,16 @@ png_write_iCCP(png_structp png_ptr, png_charp name, int compression_type,
 
    if (profile_len > 3)
       embedded_profile_len =
-          ((*( (png_bytep)profile    ))<<24) |
-          ((*( (png_bytep)profile + 1))<<16) |
-          ((*( (png_bytep)profile + 2))<< 8) |
-          ((*( (png_bytep)profile + 3))    );
+          ((*( (png_const_bytep)profile    ))<<24) |
+          ((*( (png_const_bytep)profile + 1))<<16) |
+          ((*( (png_const_bytep)profile + 2))<< 8) |
+          ((*( (png_const_bytep)profile + 3))    );
 
    if (embedded_profile_len < 0)
    {
       png_warning(png_ptr,
-        "Embedded profile length in iCCP chunk is negative");
+          "Embedded profile length in iCCP chunk is negative");
+
       png_free(png_ptr, new_name);
       return;
    }
@@ -822,7 +1135,8 @@ png_write_iCCP(png_structp png_ptr, png_charp name, int compression_type,
    if (profile_len < embedded_profile_len)
    {
       png_warning(png_ptr,
-        "Embedded profile length too large in iCCP chunk");
+          "Embedded profile length too large in iCCP chunk");
+
       png_free(png_ptr, new_name);
       return;
    }
@@ -830,23 +1144,29 @@ png_write_iCCP(png_structp png_ptr, png_charp name, int compression_type,
    if (profile_len > embedded_profile_len)
    {
       png_warning(png_ptr,
-        "Truncating profile to actual length in iCCP chunk");
+          "Truncating profile to actual length in iCCP chunk");
+
       profile_len = embedded_profile_len;
    }
 
    if (profile_len)
       profile_len = png_text_compress(png_ptr, profile,
-        (png_size_t)profile_len, PNG_COMPRESSION_TYPE_BASE, &comp);
+          (png_size_t)profile_len, PNG_COMPRESSION_TYPE_BASE, &comp);
 
    /* Make sure we include the NULL after the name and the compression type */
-   png_write_chunk_start(png_ptr, (png_bytep)png_iCCP,
-          (png_uint_32)(name_len + profile_len + 2));
+   png_write_chunk_header(png_ptr, png_iCCP,
+       (png_uint_32)(name_len + profile_len + 2));
+
    new_name[name_len + 1] = 0x00;
+
    png_write_chunk_data(png_ptr, (png_bytep)new_name,
-     (png_size_t)(name_len + 2));
+       (png_size_t)(name_len + 2));
 
    if (profile_len)
+   {
+      comp.input_len = profile_len;
       png_write_compressed_data_out(png_ptr, &comp);
+   }
 
    png_write_chunk_end(png_ptr);
    png_free(png_ptr, new_name);
@@ -856,9 +1176,8 @@ png_write_iCCP(png_structp png_ptr, png_charp name, int compression_type,
 #ifdef PNG_WRITE_sPLT_SUPPORTED
 /* Write a sPLT chunk */
 void /* PRIVATE */
-png_write_sPLT(png_structp png_ptr, png_sPLT_tp spalette)
+png_write_sPLT(png_structp png_ptr, png_const_sPLT_tp spalette)
 {
-   PNG_sPLT;
    png_size_t name_len;
    png_charp new_name;
    png_byte entrybuf[10];
@@ -875,11 +1194,13 @@ png_write_sPLT(png_structp png_ptr, png_sPLT_tp spalette)
       return;
 
    /* Make sure we include the NULL after the name */
-   png_write_chunk_start(png_ptr, (png_bytep)png_sPLT,
-     (png_uint_32)(name_len + 2 + palette_size));
+   png_write_chunk_header(png_ptr, png_sPLT,
+       (png_uint_32)(name_len + 2 + palette_size));
+
    png_write_chunk_data(png_ptr, (png_bytep)new_name,
-     (png_size_t)(name_len + 1));
-   png_write_chunk_data(png_ptr, (png_bytep)&spalette->depth, (png_size_t)1);
+       (png_size_t)(name_len + 1));
+
+   png_write_chunk_data(png_ptr, &spalette->depth, (png_size_t)1);
 
    /* Loop through each palette entry, writing appropriately */
 #ifdef PNG_POINTER_INDEXING_SUPPORTED
@@ -887,42 +1208,46 @@ png_write_sPLT(png_structp png_ptr, png_sPLT_tp spalette)
    {
       if (spalette->depth == 8)
       {
-          entrybuf[0] = (png_byte)ep->red;
-          entrybuf[1] = (png_byte)ep->green;
-          entrybuf[2] = (png_byte)ep->blue;
-          entrybuf[3] = (png_byte)ep->alpha;
-          png_save_uint_16(entrybuf + 4, ep->frequency);
+         entrybuf[0] = (png_byte)ep->red;
+         entrybuf[1] = (png_byte)ep->green;
+         entrybuf[2] = (png_byte)ep->blue;
+         entrybuf[3] = (png_byte)ep->alpha;
+         png_save_uint_16(entrybuf + 4, ep->frequency);
       }
+
       else
       {
-          png_save_uint_16(entrybuf + 0, ep->red);
-          png_save_uint_16(entrybuf + 2, ep->green);
-          png_save_uint_16(entrybuf + 4, ep->blue);
-          png_save_uint_16(entrybuf + 6, ep->alpha);
-          png_save_uint_16(entrybuf + 8, ep->frequency);
+         png_save_uint_16(entrybuf + 0, ep->red);
+         png_save_uint_16(entrybuf + 2, ep->green);
+         png_save_uint_16(entrybuf + 4, ep->blue);
+         png_save_uint_16(entrybuf + 6, ep->alpha);
+         png_save_uint_16(entrybuf + 8, ep->frequency);
       }
+
       png_write_chunk_data(png_ptr, entrybuf, (png_size_t)entry_size);
    }
 #else
    ep=spalette->entries;
-   for (i=0; i>spalette->nentries; i++)
+   for (i = 0; i>spalette->nentries; i++)
    {
       if (spalette->depth == 8)
       {
-          entrybuf[0] = (png_byte)ep[i].red;
-          entrybuf[1] = (png_byte)ep[i].green;
-          entrybuf[2] = (png_byte)ep[i].blue;
-          entrybuf[3] = (png_byte)ep[i].alpha;
-          png_save_uint_16(entrybuf + 4, ep[i].frequency);
+         entrybuf[0] = (png_byte)ep[i].red;
+         entrybuf[1] = (png_byte)ep[i].green;
+         entrybuf[2] = (png_byte)ep[i].blue;
+         entrybuf[3] = (png_byte)ep[i].alpha;
+         png_save_uint_16(entrybuf + 4, ep[i].frequency);
       }
+
       else
       {
-          png_save_uint_16(entrybuf + 0, ep[i].red);
-          png_save_uint_16(entrybuf + 2, ep[i].green);
-          png_save_uint_16(entrybuf + 4, ep[i].blue);
-          png_save_uint_16(entrybuf + 6, ep[i].alpha);
-          png_save_uint_16(entrybuf + 8, ep[i].frequency);
+         png_save_uint_16(entrybuf + 0, ep[i].red);
+         png_save_uint_16(entrybuf + 2, ep[i].green);
+         png_save_uint_16(entrybuf + 4, ep[i].blue);
+         png_save_uint_16(entrybuf + 6, ep[i].alpha);
+         png_save_uint_16(entrybuf + 8, ep[i].frequency);
       }
+
       png_write_chunk_data(png_ptr, entrybuf, (png_size_t)entry_size);
    }
 #endif
@@ -935,9 +1260,8 @@ png_write_sPLT(png_structp png_ptr, png_sPLT_tp spalette)
 #ifdef PNG_WRITE_sBIT_SUPPORTED
 /* Write the sBIT chunk */
 void /* PRIVATE */
-png_write_sBIT(png_structp png_ptr, png_color_8p sbit, int color_type)
+png_write_sBIT(png_structp png_ptr, png_const_color_8p sbit, int color_type)
 {
-   PNG_sBIT;
    png_byte buf[4];
    png_size_t size;
 
@@ -949,7 +1273,8 @@ png_write_sBIT(png_structp png_ptr, png_color_8p sbit, int color_type)
       png_byte maxbits;
 
       maxbits = (png_byte)(color_type==PNG_COLOR_TYPE_PALETTE ? 8 :
-                png_ptr->usr_bit_depth);
+          png_ptr->usr_bit_depth);
+
       if (sbit->red == 0 || sbit->red > maxbits ||
           sbit->green == 0 || sbit->green > maxbits ||
           sbit->blue == 0 || sbit->blue > maxbits)
@@ -957,11 +1282,13 @@ png_write_sBIT(png_structp png_ptr, png_color_8p sbit, int color_type)
          png_warning(png_ptr, "Invalid sBIT depth specified");
          return;
       }
+
       buf[0] = sbit->red;
       buf[1] = sbit->green;
       buf[2] = sbit->blue;
       size = 3;
    }
+
    else
    {
       if (sbit->gray == 0 || sbit->gray > png_ptr->usr_bit_depth)
@@ -969,6 +1296,7 @@ png_write_sBIT(png_structp png_ptr, png_color_8p sbit, int color_type)
          png_warning(png_ptr, "Invalid sBIT depth specified");
          return;
       }
+
       buf[0] = sbit->gray;
       size = 1;
    }
@@ -980,69 +1308,22 @@ png_write_sBIT(png_structp png_ptr, png_color_8p sbit, int color_type)
          png_warning(png_ptr, "Invalid sBIT depth specified");
          return;
       }
+
       buf[size++] = sbit->alpha;
    }
 
-   png_write_chunk(png_ptr, (png_bytep)png_sBIT, buf, size);
+   png_write_complete_chunk(png_ptr, png_sBIT, buf, size);
 }
 #endif
 
 #ifdef PNG_WRITE_cHRM_SUPPORTED
 /* Write the cHRM chunk */
-#ifdef PNG_FLOATING_POINT_SUPPORTED
-void /* PRIVATE */
-png_write_cHRM(png_structp png_ptr, double white_x, double white_y,
-   double red_x, double red_y, double green_x, double green_y,
-   double blue_x, double blue_y)
-{
-   PNG_cHRM;
-   png_byte buf[32];
-
-   png_fixed_point int_white_x, int_white_y, int_red_x, int_red_y,
-      int_green_x, int_green_y, int_blue_x, int_blue_y;
-
-   png_debug(1, "in png_write_cHRM");
-
-   int_white_x = (png_uint_32)(white_x * 100000.0 + 0.5);
-   int_white_y = (png_uint_32)(white_y * 100000.0 + 0.5);
-   int_red_x   = (png_uint_32)(red_x   * 100000.0 + 0.5);
-   int_red_y   = (png_uint_32)(red_y   * 100000.0 + 0.5);
-   int_green_x = (png_uint_32)(green_x * 100000.0 + 0.5);
-   int_green_y = (png_uint_32)(green_y * 100000.0 + 0.5);
-   int_blue_x  = (png_uint_32)(blue_x  * 100000.0 + 0.5);
-   int_blue_y  = (png_uint_32)(blue_y  * 100000.0 + 0.5);
-
-#ifdef PNG_CHECK_cHRM_SUPPORTED
-   if (png_check_cHRM_fixed(png_ptr, int_white_x, int_white_y,
-      int_red_x, int_red_y, int_green_x, int_green_y, int_blue_x, int_blue_y))
-#endif
-   {
-      /* Each value is saved in 1/100,000ths */
-
-      png_save_uint_32(buf, int_white_x);
-      png_save_uint_32(buf + 4, int_white_y);
-
-      png_save_uint_32(buf + 8, int_red_x);
-      png_save_uint_32(buf + 12, int_red_y);
-
-      png_save_uint_32(buf + 16, int_green_x);
-      png_save_uint_32(buf + 20, int_green_y);
-
-      png_save_uint_32(buf + 24, int_blue_x);
-      png_save_uint_32(buf + 28, int_blue_y);
-
-      png_write_chunk(png_ptr, (png_bytep)png_cHRM, buf, (png_size_t)32);
-   }
-}
-#endif
-#ifdef PNG_FIXED_POINT_SUPPORTED
 void /* PRIVATE */
 png_write_cHRM_fixed(png_structp png_ptr, png_fixed_point white_x,
-   png_fixed_point white_y, png_fixed_point red_x, png_fixed_point red_y,
-   png_fixed_point green_x, png_fixed_point green_y, png_fixed_point blue_x,
-   png_fixed_point blue_y)
+    png_fixed_point white_y, png_fixed_point red_x, png_fixed_point red_y,
+    png_fixed_point green_x, png_fixed_point green_y, png_fixed_point blue_x,
+    png_fixed_point blue_y)
 {
-   PNG_cHRM;
    png_byte buf[32];
 
    png_debug(1, "in png_write_cHRM");
@@ -1050,7 +1331,7 @@ png_write_cHRM_fixed(png_structp png_ptr, png_fixed_point white_x,
    /* Each value is saved in 1/100,000ths */
 #ifdef PNG_CHECK_cHRM_SUPPORTED
    if (png_check_cHRM_fixed(png_ptr, white_x, white_y, red_x, red_y,
-      green_x, green_y, blue_x, blue_y))
+       green_x, green_y, blue_x, blue_y))
 #endif
    {
       png_save_uint_32(buf, (png_uint_32)white_x);
@@ -1065,19 +1346,17 @@ png_write_cHRM_fixed(png_structp png_ptr, png_fixed_point white_x,
       png_save_uint_32(buf + 24, (png_uint_32)blue_x);
       png_save_uint_32(buf + 28, (png_uint_32)blue_y);
 
-      png_write_chunk(png_ptr, (png_bytep)png_cHRM, buf, (png_size_t)32);
+      png_write_complete_chunk(png_ptr, png_cHRM, buf, (png_size_t)32);
    }
 }
 #endif
-#endif
 
 #ifdef PNG_WRITE_tRNS_SUPPORTED
 /* Write the tRNS chunk */
 void /* PRIVATE */
-png_write_tRNS(png_structp png_ptr, png_bytep trans_alpha, png_color_16p tran,
-   int num_trans, int color_type)
+png_write_tRNS(png_structp png_ptr, png_const_bytep trans_alpha,
+    png_const_color_16p tran, int num_trans, int color_type)
 {
-   PNG_tRNS;
    png_byte buf[6];
 
    png_debug(1, "in png_write_tRNS");
@@ -1089,36 +1368,46 @@ png_write_tRNS(png_structp png_ptr, png_bytep trans_alpha, png_color_16p tran,
          png_warning(png_ptr, "Invalid number of transparent colors specified");
          return;
       }
+
       /* Write the chunk out as it is */
-      png_write_chunk(png_ptr, (png_bytep)png_tRNS, trans_alpha,
-        (png_size_t)num_trans);
+      png_write_complete_chunk(png_ptr, png_tRNS, trans_alpha, (png_size_t)num_trans);
    }
+
    else if (color_type == PNG_COLOR_TYPE_GRAY)
    {
       /* One 16 bit value */
       if (tran->gray >= (1 << png_ptr->bit_depth))
       {
          png_warning(png_ptr,
-           "Ignoring attempt to write tRNS chunk out-of-range for bit_depth");
+             "Ignoring attempt to write tRNS chunk out-of-range for bit_depth");
+
          return;
       }
+
       png_save_uint_16(buf, tran->gray);
-      png_write_chunk(png_ptr, (png_bytep)png_tRNS, buf, (png_size_t)2);
+      png_write_complete_chunk(png_ptr, png_tRNS, buf, (png_size_t)2);
    }
+
    else if (color_type == PNG_COLOR_TYPE_RGB)
    {
       /* Three 16 bit values */
       png_save_uint_16(buf, tran->red);
       png_save_uint_16(buf + 2, tran->green);
       png_save_uint_16(buf + 4, tran->blue);
+#ifdef PNG_WRITE_16BIT_SUPPORTED
       if (png_ptr->bit_depth == 8 && (buf[0] | buf[2] | buf[4]))
+#else
+      if (buf[0] | buf[2] | buf[4])
+#endif
       {
          png_warning(png_ptr,
            "Ignoring attempt to write 16-bit tRNS chunk when bit_depth is 8");
          return;
       }
-      png_write_chunk(png_ptr, (png_bytep)png_tRNS, buf, (png_size_t)6);
+
+      png_write_complete_chunk(png_ptr, png_tRNS, buf, (png_size_t)6);
    }
+
    else
    {
       png_warning(png_ptr, "Can't write tRNS with an alpha channel");
@@ -1129,9 +1418,8 @@ png_write_tRNS(png_structp png_ptr, png_bytep trans_alpha, png_color_16p tran,
 #ifdef PNG_WRITE_bKGD_SUPPORTED
 /* Write the background chunk */
 void /* PRIVATE */
-png_write_bKGD(png_structp png_ptr, png_color_16p back, int color_type)
+png_write_bKGD(png_structp png_ptr, png_const_color_16p back, int color_type)
 {
-   PNG_bKGD;
    png_byte buf[6];
 
    png_debug(1, "in png_write_bKGD");
@@ -1148,32 +1436,43 @@ png_write_bKGD(png_structp png_ptr, png_color_16p back, int color_type)
          png_warning(png_ptr, "Invalid background palette index");
          return;
       }
+
       buf[0] = back->index;
-      png_write_chunk(png_ptr, (png_bytep)png_bKGD, buf, (png_size_t)1);
+      png_write_complete_chunk(png_ptr, png_bKGD, buf, (png_size_t)1);
    }
+
    else if (color_type & PNG_COLOR_MASK_COLOR)
    {
       png_save_uint_16(buf, back->red);
       png_save_uint_16(buf + 2, back->green);
       png_save_uint_16(buf + 4, back->blue);
+#ifdef PNG_WRITE_16BIT_SUPPORTED
       if (png_ptr->bit_depth == 8 && (buf[0] | buf[2] | buf[4]))
+#else
+      if (buf[0] | buf[2] | buf[4])
+#endif
       {
          png_warning(png_ptr,
-           "Ignoring attempt to write 16-bit bKGD chunk when bit_depth is 8");
+             "Ignoring attempt to write 16-bit bKGD chunk when bit_depth is 8");
+
          return;
       }
-      png_write_chunk(png_ptr, (png_bytep)png_bKGD, buf, (png_size_t)6);
+
+      png_write_complete_chunk(png_ptr, png_bKGD, buf, (png_size_t)6);
    }
+
    else
    {
       if (back->gray >= (1 << png_ptr->bit_depth))
       {
          png_warning(png_ptr,
-           "Ignoring attempt to write bKGD chunk out-of-range for bit_depth");
+             "Ignoring attempt to write bKGD chunk out-of-range for bit_depth");
+
          return;
       }
+
       png_save_uint_16(buf, back->gray);
-      png_write_chunk(png_ptr, (png_bytep)png_bKGD, buf, (png_size_t)2);
+      png_write_complete_chunk(png_ptr, png_bKGD, buf, (png_size_t)2);
    }
 }
 #endif
@@ -1181,9 +1480,8 @@ png_write_bKGD(png_structp png_ptr, png_color_16p back, int color_type)
 #ifdef PNG_WRITE_hIST_SUPPORTED
 /* Write the histogram */
 void /* PRIVATE */
-png_write_hIST(png_structp png_ptr, png_uint_16p hist, int num_hist)
+png_write_hIST(png_structp png_ptr, png_const_uint_16p hist, int num_hist)
 {
-   PNG_hIST;
    int i;
    png_byte buf[3];
 
@@ -1192,18 +1490,20 @@ png_write_hIST(png_structp png_ptr, png_uint_16p hist, int num_hist)
    if (num_hist > (int)png_ptr->num_palette)
    {
       png_debug2(3, "num_hist = %d, num_palette = %d", num_hist,
-         png_ptr->num_palette);
+          png_ptr->num_palette);
+
       png_warning(png_ptr, "Invalid number of histogram entries specified");
       return;
    }
 
-   png_write_chunk_start(png_ptr, (png_bytep)png_hIST,
-     (png_uint_32)(num_hist * 2));
+   png_write_chunk_header(png_ptr, png_hIST, (png_uint_32)(num_hist * 2));
+
    for (i = 0; i < num_hist; i++)
    {
       png_save_uint_16(buf, hist[i]);
       png_write_chunk_data(png_ptr, buf, (png_size_t)2);
    }
+
    png_write_chunk_end(png_ptr);
 }
 #endif
@@ -1221,9 +1521,10 @@ png_write_hIST(png_structp png_ptr, png_uint_16p hist, int num_hist)
  * static keywords without having to have duplicate copies of the strings.
  */
 png_size_t /* PRIVATE */
-png_check_keyword(png_structp png_ptr, png_charp key, png_charpp new_key)
+png_check_keyword(png_structp png_ptr, png_const_charp key, png_charpp new_key)
 {
    png_size_t key_len;
+   png_const_charp ikp;
    png_charp kp, dp;
    int kflag;
    int kwarn=0;
@@ -1241,6 +1542,7 @@ png_check_keyword(png_structp png_ptr, png_charp key, png_charpp new_key)
    png_debug1(2, "Keyword to be checked is '%s'", key);
 
    *new_key = (png_charp)png_malloc_warn(png_ptr, (png_uint_32)(key_len + 2));
+
    if (*new_key == NULL)
    {
       png_warning(png_ptr, "Out of memory while procesing keyword");
@@ -1248,25 +1550,22 @@ png_check_keyword(png_structp png_ptr, png_charp key, png_charpp new_key)
    }
 
    /* Replace non-printing characters with a blank and print a warning */
-   for (kp = key, dp = *new_key; *kp != '\0'; kp++, dp++)
+   for (ikp = key, dp = *new_key; *ikp != '\0'; ikp++, dp++)
    {
-      if ((png_byte)*kp < 0x20 ||
-         ((png_byte)*kp > 0x7E && (png_byte)*kp < 0xA1))
+      if ((png_byte)*ikp < 0x20 ||
+         ((png_byte)*ikp > 0x7E && (png_byte)*ikp < 0xA1))
       {
-#ifdef PNG_STDIO_SUPPORTED
-         char msg[40];
+         PNG_WARNING_PARAMETERS(p)
 
-         png_snprintf(msg, 40,
-           "invalid keyword character 0x%02X", (png_byte)*kp);
-         png_warning(png_ptr, msg);
-#else
-         png_warning(png_ptr, "invalid character in keyword");
-#endif
+         png_warning_parameter_unsigned(p, 1, PNG_NUMBER_FORMAT_02x,
+            (png_byte)*ikp);
+         png_formatted_warning(png_ptr, p, "invalid keyword character 0x@1");
          *dp = ' ';
       }
+
       else
       {
-         *dp = *kp;
+         *dp = *ikp;
       }
    }
    *dp = '\0';
@@ -1307,11 +1606,13 @@ png_check_keyword(png_structp png_ptr, png_charp key, png_charpp new_key)
          *(dp++) = *kp;
          kflag = 1;
       }
+
       else if (*kp == ' ')
       {
          key_len--;
-         kwarn=1;
+         kwarn = 1;
       }
+
       else
       {
          *(dp++) = *kp;
@@ -1342,10 +1643,9 @@ png_check_keyword(png_structp png_ptr, png_charp key, png_charpp new_key)
 #ifdef PNG_WRITE_tEXt_SUPPORTED
 /* Write a tEXt chunk */
 void /* PRIVATE */
-png_write_tEXt(png_structp png_ptr, png_charp key, png_charp text,
-   png_size_t text_len)
+png_write_tEXt(png_structp png_ptr, png_const_charp key, png_const_charp text,
+    png_size_t text_len)
 {
-   PNG_tEXt;
    png_size_t key_len;
    png_charp new_key;
 
@@ -1356,12 +1656,13 @@ png_write_tEXt(png_structp png_ptr, png_charp key, png_charp text,
 
    if (text == NULL || *text == '\0')
       text_len = 0;
+
    else
       text_len = png_strlen(text);
 
    /* Make sure we include the 0 after the key */
-   png_write_chunk_start(png_ptr, (png_bytep)png_tEXt,
-      (png_uint_32)(key_len + text_len + 1));
+   png_write_chunk_header(png_ptr, png_tEXt,
+       (png_uint_32)(key_len + text_len + 1));
    /*
     * We leave it to the application to meet PNG-1.0 requirements on the
     * contents of the text.  PNG-1.0 through PNG-1.2 discourage the use of
@@ -1369,9 +1670,11 @@ png_write_tEXt(png_structp png_ptr, png_charp key, png_charp text,
     * The NUL character is forbidden by PNG-1.0 through PNG-1.2 and ISO PNG.
     */
    png_write_chunk_data(png_ptr, (png_bytep)new_key,
-     (png_size_t)(key_len + 1));
+       (png_size_t)(key_len + 1));
+
    if (text_len)
-      png_write_chunk_data(png_ptr, (png_bytep)text, (png_size_t)text_len);
+      png_write_chunk_data(png_ptr, (png_const_bytep)text,
+          (png_size_t)text_len);
 
    png_write_chunk_end(png_ptr);
    png_free(png_ptr, new_key);
@@ -1381,12 +1684,11 @@ png_write_tEXt(png_structp png_ptr, png_charp key, png_charp text,
 #ifdef PNG_WRITE_zTXt_SUPPORTED
 /* Write a compressed text chunk */
 void /* PRIVATE */
-png_write_zTXt(png_structp png_ptr, png_charp key, png_charp text,
-   png_size_t text_len, int compression)
+png_write_zTXt(png_structp png_ptr, png_const_charp key, png_const_charp text,
+    png_size_t text_len, int compression)
 {
-   PNG_zTXt;
    png_size_t key_len;
-   char buf[1];
+   png_byte buf;
    png_charp new_key;
    compression_state comp;
 
@@ -1398,7 +1700,7 @@ png_write_zTXt(png_structp png_ptr, png_charp key, png_charp text,
    comp.input = NULL;
    comp.input_len = 0;
 
-   if ((key_len = png_check_keyword(png_ptr, key, &new_key))==0)
+   if ((key_len = png_check_keyword(png_ptr, key, &new_key)) == 0)
    {
       png_free(png_ptr, new_key);
       return;
@@ -1418,17 +1720,22 @@ png_write_zTXt(png_structp png_ptr, png_charp key, png_charp text,
        &comp);
 
    /* Write start of chunk */
-   png_write_chunk_start(png_ptr, (png_bytep)png_zTXt,
-     (png_uint_32)(key_len+text_len + 2));
+   png_write_chunk_header(png_ptr, png_zTXt,
+       (png_uint_32)(key_len+text_len + 2));
+
    /* Write key */
    png_write_chunk_data(png_ptr, (png_bytep)new_key,
-     (png_size_t)(key_len + 1));
+       (png_size_t)(key_len + 1));
+
    png_free(png_ptr, new_key);
 
-   buf[0] = (png_byte)compression;
+   buf = (png_byte)compression;
+
    /* Write compression */
-   png_write_chunk_data(png_ptr, (png_bytep)buf, (png_size_t)1);
+   png_write_chunk_data(png_ptr, &buf, (png_size_t)1);
+
    /* Write the compressed data */
+   comp.input_len = text_len;
    png_write_compressed_data_out(png_ptr, &comp);
 
    /* Close the chunk */
@@ -1439,10 +1746,9 @@ png_write_zTXt(png_structp png_ptr, png_charp key, png_charp text,
 #ifdef PNG_WRITE_iTXt_SUPPORTED
 /* Write an iTXt chunk */
 void /* PRIVATE */
-png_write_iTXt(png_structp png_ptr, int compression, png_charp key,
-    png_charp lang, png_charp lang_key, png_charp text)
+png_write_iTXt(png_structp png_ptr, int compression, png_const_charp key,
+    png_const_charp lang, png_const_charp lang_key, png_const_charp text)
 {
-   PNG_iTXt;
    png_size_t lang_len, key_len, lang_key_len, text_len;
    png_charp new_lang;
    png_charp new_key = NULL;
@@ -1456,10 +1762,10 @@ png_write_iTXt(png_structp png_ptr, int compression, png_charp key,
    comp.output_ptr = NULL;
    comp.input = NULL;
 
-   if ((key_len = png_check_keyword(png_ptr, key, &new_key))==0)
+   if ((key_len = png_check_keyword(png_ptr, key, &new_key)) == 0)
       return;
 
-   if ((lang_len = png_check_keyword(png_ptr, lang, &new_lang))==0)
+   if ((lang_len = png_check_keyword(png_ptr, lang, &new_lang)) == 0)
    {
       png_warning(png_ptr, "Empty language field in iTXt chunk");
       new_lang = NULL;
@@ -1468,24 +1774,26 @@ png_write_iTXt(png_structp png_ptr, int compression, png_charp key,
 
    if (lang_key == NULL)
       lang_key_len = 0;
+
    else
       lang_key_len = png_strlen(lang_key);
 
    if (text == NULL)
       text_len = 0;
+
    else
       text_len = png_strlen(text);
 
    /* Compute the compressed data; do it now for the length */
-   text_len = png_text_compress(png_ptr, text, text_len, compression-2,
-      &comp);
+   text_len = png_text_compress(png_ptr, text, text_len, compression - 2,
+       &comp);
 
 
    /* Make sure we include the compression flag, the compression byte,
-    * and the NULs after the key, lang, and lang_key parts */
+    * and the NULs after the key, lang, and lang_key parts
+    */
 
-   png_write_chunk_start(png_ptr, (png_bytep)png_iTXt,
-          (png_uint_32)(
+   png_write_chunk_header(png_ptr, png_iTXt, (png_uint_32)(
         5 /* comp byte, comp flag, terminators for key, lang and lang_key */
         + key_len
         + lang_len
@@ -1497,27 +1805,32 @@ png_write_iTXt(png_structp png_ptr, int compression, png_charp key,
     * any non-Latin-1 characters except for NEWLINE.  ISO PNG will forbid them.
     * The NUL character is forbidden by PNG-1.0 through PNG-1.2 and ISO PNG.
     */
-   png_write_chunk_data(png_ptr, (png_bytep)new_key,
-     (png_size_t)(key_len + 1));
+   png_write_chunk_data(png_ptr, (png_bytep)new_key, (png_size_t)(key_len + 1));
 
    /* Set the compression flag */
-   if (compression == PNG_ITXT_COMPRESSION_NONE || \
+   if (compression == PNG_ITXT_COMPRESSION_NONE ||
        compression == PNG_TEXT_COMPRESSION_NONE)
-       cbuf[0] = 0;
+      cbuf[0] = 0;
+
    else /* compression == PNG_ITXT_COMPRESSION_zTXt */
-       cbuf[0] = 1;
+      cbuf[0] = 1;
+
    /* Set the compression method */
    cbuf[1] = 0;
+
    png_write_chunk_data(png_ptr, cbuf, (png_size_t)2);
 
    cbuf[0] = 0;
-   png_write_chunk_data(png_ptr, (new_lang ? (png_bytep)new_lang : cbuf),
-     (png_size_t)(lang_len + 1));
-   png_write_chunk_data(png_ptr, (lang_key ? (png_bytep)lang_key : cbuf),
-     (png_size_t)(lang_key_len + 1));
+   png_write_chunk_data(png_ptr, (new_lang ? (png_const_bytep)new_lang : cbuf),
+       (png_size_t)(lang_len + 1));
+
+   png_write_chunk_data(png_ptr, (lang_key ? (png_const_bytep)lang_key : cbuf),
+       (png_size_t)(lang_key_len + 1));
+
    png_write_compressed_data_out(png_ptr, &comp);
 
    png_write_chunk_end(png_ptr);
+
    png_free(png_ptr, new_key);
    png_free(png_ptr, new_lang);
 }
@@ -1527,9 +1840,8 @@ png_write_iTXt(png_structp png_ptr, int compression, png_charp key,
 /* Write the oFFs chunk */
 void /* PRIVATE */
 png_write_oFFs(png_structp png_ptr, png_int_32 x_offset, png_int_32 y_offset,
-   int unit_type)
+    int unit_type)
 {
-   PNG_oFFs;
    png_byte buf[9];
 
    png_debug(1, "in png_write_oFFs");
@@ -1541,18 +1853,18 @@ png_write_oFFs(png_structp png_ptr, png_int_32 x_offset, png_int_32 y_offset,
    png_save_int_32(buf + 4, y_offset);
    buf[8] = (png_byte)unit_type;
 
-   png_write_chunk(png_ptr, (png_bytep)png_oFFs, buf, (png_size_t)9);
+   png_write_complete_chunk(png_ptr, png_oFFs, buf, (png_size_t)9);
 }
 #endif
 #ifdef PNG_WRITE_pCAL_SUPPORTED
 /* Write the pCAL chunk (described in the PNG extensions document) */
 void /* PRIVATE */
 png_write_pCAL(png_structp png_ptr, png_charp purpose, png_int_32 X0,
-   png_int_32 X1, int type, int nparams, png_charp units, png_charpp params)
+    png_int_32 X1, int type, int nparams, png_const_charp units,
+    png_charpp params)
 {
-   PNG_pCAL;
    png_size_t purpose_len, units_len, total_len;
-   png_uint_32p params_len;
+   png_size_tp params_len;
    png_byte buf[10];
    png_charp new_purpose;
    int i;
@@ -1568,36 +1880,35 @@ png_write_pCAL(png_structp png_ptr, png_charp purpose, png_int_32 X0,
    png_debug1(3, "pCAL units length = %d", (int)units_len);
    total_len = purpose_len + units_len + 10;
 
-   params_len = (png_uint_32p)png_malloc(png_ptr,
-      (png_alloc_size_t)(nparams * png_sizeof(png_uint_32)));
+   params_len = (png_size_tp)png_malloc(png_ptr,
+       (png_alloc_size_t)(nparams * png_sizeof(png_size_t)));
 
    /* Find the length of each parameter, making sure we don't count the
-      null terminator for the last parameter. */
+    * null terminator for the last parameter.
+    */
    for (i = 0; i < nparams; i++)
    {
       params_len[i] = png_strlen(params[i]) + (i == nparams - 1 ? 0 : 1);
       png_debug2(3, "pCAL parameter %d length = %lu", i,
-        (unsigned long) params_len[i]);
-      total_len += (png_size_t)params_len[i];
+          (unsigned long)params_len[i]);
+      total_len += params_len[i];
    }
 
    png_debug1(3, "pCAL total length = %d", (int)total_len);
-   png_write_chunk_start(png_ptr, (png_bytep)png_pCAL, (png_uint_32)total_len);
-   png_write_chunk_data(png_ptr, (png_bytep)new_purpose,
-     (png_size_t)purpose_len);
+   png_write_chunk_header(png_ptr, png_pCAL, (png_uint_32)total_len);
+   png_write_chunk_data(png_ptr, (png_const_bytep)new_purpose, purpose_len);
    png_save_int_32(buf, X0);
    png_save_int_32(buf + 4, X1);
    buf[8] = (png_byte)type;
    buf[9] = (png_byte)nparams;
    png_write_chunk_data(png_ptr, buf, (png_size_t)10);
-   png_write_chunk_data(png_ptr, (png_bytep)units, (png_size_t)units_len);
+   png_write_chunk_data(png_ptr, (png_const_bytep)units, (png_size_t)units_len);
 
    png_free(png_ptr, new_purpose);
 
    for (i = 0; i < nparams; i++)
    {
-      png_write_chunk_data(png_ptr, (png_bytep)params[i],
-         (png_size_t)params_len[i]);
+      png_write_chunk_data(png_ptr, (png_const_bytep)params[i], params_len[i]);
    }
 
    png_free(png_ptr, params_len);
@@ -1607,32 +1918,10 @@ png_write_pCAL(png_structp png_ptr, png_charp purpose, png_int_32 X0,
 
 #ifdef PNG_WRITE_sCAL_SUPPORTED
 /* Write the sCAL chunk */
-#if defined(PNG_FLOATING_POINT_SUPPORTED) && defined(PNG_STDIO_SUPPORTED)
-void /* PRIVATE */
-png_write_sCAL(png_structp png_ptr, int unit, double width, double height)
-{
-   PNG_sCAL;
-   char buf[64];
-   png_size_t total_len;
-
-   png_debug(1, "in png_write_sCAL");
-
-   buf[0] = (char)unit;
-   png_snprintf(buf + 1, 63, "%12.12e", width);
-   total_len = 1 + png_strlen(buf + 1) + 1;
-   png_snprintf(buf + total_len, 64-total_len, "%12.12e", height);
-   total_len += png_strlen(buf + total_len);
-
-   png_debug1(3, "sCAL total length = %u", (unsigned int)total_len);
-   png_write_chunk(png_ptr, (png_bytep)png_sCAL, (png_bytep)buf, total_len);
-}
-#else
-#ifdef PNG_FIXED_POINT_SUPPORTED
 void /* PRIVATE */
-png_write_sCAL_s(png_structp png_ptr, int unit, png_charp width,
-   png_charp height)
+png_write_sCAL_s(png_structp png_ptr, int unit, png_const_charp width,
+    png_const_charp height)
 {
-   PNG_sCAL;
    png_byte buf[64];
    png_size_t wlen, hlen, total_len;
 
@@ -1641,6 +1930,7 @@ png_write_sCAL_s(png_structp png_ptr, int unit, png_charp width,
    wlen = png_strlen(width);
    hlen = png_strlen(height);
    total_len = wlen + hlen + 2;
+
    if (total_len > 64)
    {
       png_warning(png_ptr, "Can't write sCAL (buffer too small)");
@@ -1652,20 +1942,17 @@ png_write_sCAL_s(png_structp png_ptr, int unit, png_charp width,
    png_memcpy(buf + wlen + 2, height, hlen);  /* Do NOT append the '\0' here */
 
    png_debug1(3, "sCAL total length = %u", (unsigned int)total_len);
-   png_write_chunk(png_ptr, (png_bytep)png_sCAL, buf, total_len);
+   png_write_complete_chunk(png_ptr, png_sCAL, buf, total_len);
 }
 #endif
-#endif
-#endif
 
 #ifdef PNG_WRITE_pHYs_SUPPORTED
 /* Write the pHYs chunk */
 void /* PRIVATE */
 png_write_pHYs(png_structp png_ptr, png_uint_32 x_pixels_per_unit,
-   png_uint_32 y_pixels_per_unit,
-   int unit_type)
+    png_uint_32 y_pixels_per_unit,
+    int unit_type)
 {
-   PNG_pHYs;
    png_byte buf[9];
 
    png_debug(1, "in png_write_pHYs");
@@ -1677,7 +1964,7 @@ png_write_pHYs(png_structp png_ptr, png_uint_32 x_pixels_per_unit,
    png_save_uint_32(buf + 4, y_pixels_per_unit);
    buf[8] = (png_byte)unit_type;
 
-   png_write_chunk(png_ptr, (png_bytep)png_pHYs, buf, (png_size_t)9);
+   png_write_complete_chunk(png_ptr, png_pHYs, buf, (png_size_t)9);
 }
 #endif
 
@@ -1686,9 +1973,8 @@ png_write_pHYs(png_structp png_ptr, png_uint_32 x_pixels_per_unit,
  * or png_convert_from_time_t(), or fill in the structure yourself.
  */
 void /* PRIVATE */
-png_write_tIME(png_structp png_ptr, png_timep mod_time)
+png_write_tIME(png_structp png_ptr, png_const_timep mod_time)
 {
-   PNG_tIME;
    png_byte buf[7];
 
    png_debug(1, "in png_write_tIME");
@@ -1708,7 +1994,7 @@ png_write_tIME(png_structp png_ptr, png_timep mod_time)
    buf[5] = mod_time->minute;
    buf[6] = mod_time->second;
 
-   png_write_chunk(png_ptr, (png_bytep)png_tIME, buf, (png_size_t)7);
+   png_write_complete_chunk(png_ptr, png_tIME, buf, (png_size_t)7);
 }
 #endif
 
@@ -1720,36 +2006,41 @@ png_write_start_row(png_structp png_ptr)
    /* Arrays to facilitate easy interlacing - use pass (0 - 6) as index */
 
    /* Start of interlace block */
-   int png_pass_start[7] = {0, 4, 0, 2, 0, 1, 0};
+   static PNG_CONST png_byte png_pass_start[7] = {0, 4, 0, 2, 0, 1, 0};
 
    /* Offset to next interlace block */
-   int png_pass_inc[7] = {8, 8, 4, 4, 2, 2, 1};
+   static PNG_CONST png_byte png_pass_inc[7] = {8, 8, 4, 4, 2, 2, 1};
 
    /* Start of interlace block in the y direction */
-   int png_pass_ystart[7] = {0, 0, 4, 0, 2, 0, 1};
+   static PNG_CONST png_byte png_pass_ystart[7] = {0, 0, 4, 0, 2, 0, 1};
 
    /* Offset to next interlace block in the y direction */
-   int png_pass_yinc[7] = {8, 8, 8, 4, 4, 2, 2};
+   static PNG_CONST png_byte png_pass_yinc[7] = {8, 8, 8, 4, 4, 2, 2};
 #endif
 
-   png_size_t buf_size;
+   png_alloc_size_t buf_size;
+   int usr_pixel_depth;
 
    png_debug(1, "in png_write_start_row");
 
-   buf_size = (png_size_t)(PNG_ROWBYTES(
-      png_ptr->usr_channels*png_ptr->usr_bit_depth, png_ptr->width) + 1);
+   usr_pixel_depth = png_ptr->usr_channels * png_ptr->usr_bit_depth;
+   buf_size = PNG_ROWBYTES(usr_pixel_depth, png_ptr->width) + 1;
+
+   /* 1.5.6: added to allow checking in the row write code. */
+   png_ptr->transformed_pixel_depth = png_ptr->pixel_depth;
+   png_ptr->maximum_pixel_depth = (png_byte)usr_pixel_depth;
 
    /* Set up row buffer */
-   png_ptr->row_buf = (png_bytep)png_malloc(png_ptr,
-     (png_alloc_size_t)buf_size);
+   png_ptr->row_buf = (png_bytep)png_malloc(png_ptr, buf_size);
+
    png_ptr->row_buf[0] = PNG_FILTER_VALUE_NONE;
 
 #ifdef PNG_WRITE_FILTER_SUPPORTED
    /* Set up filtering buffer, if using this filter */
    if (png_ptr->do_filter & PNG_FILTER_SUB)
    {
-      png_ptr->sub_row = (png_bytep)png_malloc(png_ptr,
-         (png_alloc_size_t)(png_ptr->rowbytes + 1));
+      png_ptr->sub_row = (png_bytep)png_malloc(png_ptr, png_ptr->rowbytes + 1);
+
       png_ptr->sub_row[0] = PNG_FILTER_VALUE_SUB;
    }
 
@@ -1757,27 +2048,29 @@ png_write_start_row(png_structp png_ptr)
    if (png_ptr->do_filter & (PNG_FILTER_AVG | PNG_FILTER_UP | PNG_FILTER_PAETH))
    {
       /* Set up previous row buffer */
-      png_ptr->prev_row = (png_bytep)png_calloc(png_ptr,
-         (png_alloc_size_t)buf_size);
+      png_ptr->prev_row = (png_bytep)png_calloc(png_ptr, buf_size);
 
       if (png_ptr->do_filter & PNG_FILTER_UP)
       {
          png_ptr->up_row = (png_bytep)png_malloc(png_ptr,
-            (png_size_t)(png_ptr->rowbytes + 1));
+            png_ptr->rowbytes + 1);
+
          png_ptr->up_row[0] = PNG_FILTER_VALUE_UP;
       }
 
       if (png_ptr->do_filter & PNG_FILTER_AVG)
       {
          png_ptr->avg_row = (png_bytep)png_malloc(png_ptr,
-            (png_alloc_size_t)(png_ptr->rowbytes + 1));
+             png_ptr->rowbytes + 1);
+
          png_ptr->avg_row[0] = PNG_FILTER_VALUE_AVG;
       }
 
       if (png_ptr->do_filter & PNG_FILTER_PAETH)
       {
          png_ptr->paeth_row = (png_bytep)png_malloc(png_ptr,
-            (png_size_t)(png_ptr->rowbytes + 1));
+             png_ptr->rowbytes + 1);
+
          png_ptr->paeth_row[0] = PNG_FILTER_VALUE_PAETH;
       }
    }
@@ -1790,22 +2083,27 @@ png_write_start_row(png_structp png_ptr)
       if (!(png_ptr->transformations & PNG_INTERLACE))
       {
          png_ptr->num_rows = (png_ptr->height + png_pass_yinc[0] - 1 -
-            png_pass_ystart[0]) / png_pass_yinc[0];
+             png_pass_ystart[0]) / png_pass_yinc[0];
+
          png_ptr->usr_width = (png_ptr->width + png_pass_inc[0] - 1 -
-            png_pass_start[0]) / png_pass_inc[0];
+             png_pass_start[0]) / png_pass_inc[0];
       }
+
       else
       {
          png_ptr->num_rows = png_ptr->height;
          png_ptr->usr_width = png_ptr->width;
       }
    }
+
    else
 #endif
    {
       png_ptr->num_rows = png_ptr->height;
       png_ptr->usr_width = png_ptr->width;
    }
+
+   png_zlib_claim(png_ptr, PNG_ZLIB_FOR_IDAT);
    png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
    png_ptr->zstream.next_out = png_ptr->zbuf;
 }
@@ -1818,16 +2116,16 @@ png_write_finish_row(png_structp png_ptr)
    /* Arrays to facilitate easy interlacing - use pass (0 - 6) as index */
 
    /* Start of interlace block */
-   int png_pass_start[7] = {0, 4, 0, 2, 0, 1, 0};
+   static PNG_CONST png_byte png_pass_start[7] = {0, 4, 0, 2, 0, 1, 0};
 
    /* Offset to next interlace block */
-   int png_pass_inc[7] = {8, 8, 4, 4, 2, 2, 1};
+   static PNG_CONST png_byte png_pass_inc[7] = {8, 8, 4, 4, 2, 2, 1};
 
    /* Start of interlace block in the y direction */
-   int png_pass_ystart[7] = {0, 0, 4, 0, 2, 0, 1};
+   static PNG_CONST png_byte png_pass_ystart[7] = {0, 0, 4, 0, 2, 0, 1};
 
    /* Offset to next interlace block in the y direction */
-   int png_pass_yinc[7] = {8, 8, 8, 4, 4, 2, 2};
+   static PNG_CONST png_byte png_pass_yinc[7] = {8, 8, 8, 4, 4, 2, 2};
 #endif
 
    int ret;
@@ -1850,24 +2148,30 @@ png_write_finish_row(png_structp png_ptr)
       {
          png_ptr->pass++;
       }
+
       else
       {
          /* Loop until we find a non-zero width or height pass */
          do
          {
             png_ptr->pass++;
+
             if (png_ptr->pass >= 7)
                break;
+
             png_ptr->usr_width = (png_ptr->width +
-               png_pass_inc[png_ptr->pass] - 1 -
-               png_pass_start[png_ptr->pass]) /
-               png_pass_inc[png_ptr->pass];
+                png_pass_inc[png_ptr->pass] - 1 -
+                png_pass_start[png_ptr->pass]) /
+                png_pass_inc[png_ptr->pass];
+
             png_ptr->num_rows = (png_ptr->height +
-               png_pass_yinc[png_ptr->pass] - 1 -
-               png_pass_ystart[png_ptr->pass]) /
-               png_pass_yinc[png_ptr->pass];
+                png_pass_yinc[png_ptr->pass] - 1 -
+                png_pass_ystart[png_ptr->pass]) /
+                png_pass_yinc[png_ptr->pass];
+
             if (png_ptr->transformations & PNG_INTERLACE)
                break;
+
          } while (png_ptr->usr_width == 0 || png_ptr->num_rows == 0);
 
       }
@@ -1877,8 +2181,9 @@ png_write_finish_row(png_structp png_ptr)
       {
          if (png_ptr->prev_row != NULL)
             png_memset(png_ptr->prev_row, 0,
-               (png_size_t)(PNG_ROWBYTES(png_ptr->usr_channels*
-               png_ptr->usr_bit_depth, png_ptr->width)) + 1);
+                (png_size_t)(PNG_ROWBYTES(png_ptr->usr_channels*
+                png_ptr->usr_bit_depth, png_ptr->width)) + 1);
+
          return;
       }
    }
@@ -1890,6 +2195,7 @@ png_write_finish_row(png_structp png_ptr)
    {
       /* Tell the compressor we are done */
       ret = deflate(&png_ptr->zstream, Z_FINISH);
+
       /* Check for an error */
       if (ret == Z_OK)
       {
@@ -1901,10 +2207,12 @@ png_write_finish_row(png_structp png_ptr)
             png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
          }
       }
+
       else if (ret != Z_STREAM_END)
       {
          if (png_ptr->zstream.msg != NULL)
             png_error(png_ptr, png_ptr->zstream.msg);
+
          else
             png_error(png_ptr, "zlib error");
       }
@@ -1914,10 +2222,10 @@ png_write_finish_row(png_structp png_ptr)
    if (png_ptr->zstream.avail_out < png_ptr->zbuf_size)
    {
       png_write_IDAT(png_ptr, png_ptr->zbuf, png_ptr->zbuf_size -
-         png_ptr->zstream.avail_out);
+          png_ptr->zstream.avail_out);
    }
 
-   deflateReset(&png_ptr->zstream);
+   png_zlib_release(png_ptr);
    png_ptr->zstream.data_type = Z_BINARY;
 }
 
@@ -1935,10 +2243,10 @@ png_do_write_interlace(png_row_infop row_info, png_bytep row, int pass)
    /* Arrays to facilitate easy interlacing - use pass (0 - 6) as index */
 
    /* Start of interlace block */
-   int png_pass_start[7] = {0, 4, 0, 2, 0, 1, 0};
+   static PNG_CONST png_byte png_pass_start[7] = {0, 4, 0, 2, 0, 1, 0};
 
    /* Offset to next interlace block */
-   int png_pass_inc[7] = {8, 8, 4, 4, 2, 2, 1};
+   static PNG_CONST png_byte  png_pass_inc[7] = {8, 8, 4, 4, 2, 2, 1};
 
    png_debug(1, "in png_do_write_interlace");
 
@@ -1961,6 +2269,7 @@ png_do_write_interlace(png_row_infop row_info, png_bytep row, int pass)
             dp = row;
             d = 0;
             shift = 7;
+
             for (i = png_pass_start[pass]; i < row_width;
                i += png_pass_inc[pass])
             {
@@ -1974,14 +2283,17 @@ png_do_write_interlace(png_row_infop row_info, png_bytep row, int pass)
                   *dp++ = (png_byte)d;
                   d = 0;
                }
+
                else
                   shift--;
 
             }
             if (shift != 7)
                *dp = (png_byte)d;
+
             break;
          }
+
          case 2:
          {
             png_bytep sp;
@@ -1995,6 +2307,7 @@ png_do_write_interlace(png_row_infop row_info, png_bytep row, int pass)
             dp = row;
             shift = 6;
             d = 0;
+
             for (i = png_pass_start[pass]; i < row_width;
                i += png_pass_inc[pass])
             {
@@ -2008,13 +2321,16 @@ png_do_write_interlace(png_row_infop row_info, png_bytep row, int pass)
                   *dp++ = (png_byte)d;
                   d = 0;
                }
+
                else
                   shift -= 2;
             }
             if (shift != 6)
-                   *dp = (png_byte)d;
+               *dp = (png_byte)d;
+
             break;
          }
+
          case 4:
          {
             png_bytep sp;
@@ -2029,7 +2345,7 @@ png_do_write_interlace(png_row_infop row_info, png_bytep row, int pass)
             shift = 4;
             d = 0;
             for (i = png_pass_start[pass]; i < row_width;
-               i += png_pass_inc[pass])
+                i += png_pass_inc[pass])
             {
                sp = row + (png_size_t)(i >> 1);
                value = (*sp >> ((1 - (int)(i & 0x01)) << 2)) & 0x0f;
@@ -2041,13 +2357,16 @@ png_do_write_interlace(png_row_infop row_info, png_bytep row, int pass)
                   *dp++ = (png_byte)d;
                   d = 0;
                }
+
                else
                   shift -= 4;
             }
             if (shift != 4)
                *dp = (png_byte)d;
+
             break;
          }
+
          default:
          {
             png_bytep sp;
@@ -2058,18 +2377,21 @@ png_do_write_interlace(png_row_infop row_info, png_bytep row, int pass)
 
             /* Start at the beginning */
             dp = row;
+
             /* Find out how many bytes each pixel takes up */
             pixel_bytes = (row_info->pixel_depth >> 3);
-            /* Loop through the row, only looking at the pixels that
-               matter */
+
+            /* Loop through the row, only looking at the pixels that matter */
             for (i = png_pass_start[pass]; i < row_width;
                i += png_pass_inc[pass])
             {
                /* Find out where the original pixel is */
                sp = row + (png_size_t)i * pixel_bytes;
+
                /* Move the pixel */
                if (dp != sp)
                   png_memcpy(dp, sp, pixel_bytes);
+
                /* Next pixel */
                dp += pixel_bytes;
             }
@@ -2078,11 +2400,12 @@ png_do_write_interlace(png_row_infop row_info, png_bytep row, int pass)
       }
       /* Set new row width */
       row_info->width = (row_info->width +
-         png_pass_inc[pass] - 1 -
-         png_pass_start[pass]) /
-         png_pass_inc[pass];
-         row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth,
-            row_info->width);
+          png_pass_inc[pass] - 1 -
+          png_pass_start[pass]) /
+          png_pass_inc[pass];
+
+      row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth,
+          row_info->width);
    }
 }
 #endif
@@ -2091,6 +2414,9 @@ png_do_write_interlace(png_row_infop row_info, png_bytep row, int pass)
  * been specified by the application, and then writes the row out with the
  * chosen filter.
  */
+static void png_write_filtered_row(png_structp png_ptr, png_bytep filtered_row,
+   png_size_t row_bytes);
+
 #define PNG_MAXSUM (((png_uint_32)(-1)) >> 1)
 #define PNG_HISHIFT 10
 #define PNG_LOMASK ((png_uint_32)0xffffL)
@@ -2103,9 +2429,9 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
    png_bytep prev_row, row_buf;
    png_uint_32 mins, bpp;
    png_byte filter_to_do = png_ptr->do_filter;
-   png_uint_32 row_bytes = row_info->rowbytes;
+   png_size_t row_bytes = row_info->rowbytes;
 #ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED
-   int num_p_filters = (int)png_ptr->num_prev_filters;
+   int num_p_filters = png_ptr->num_prev_filters;
 #endif
 
    png_debug(1, "in png_write_find_filter");
@@ -2113,8 +2439,8 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
 #ifndef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED
   if (png_ptr->row_number == 0 && filter_to_do == PNG_ALL_FILTERS)
   {
-      /* These will never be selected so we need not test them. */
-      filter_to_do &= ~(PNG_FILTER_UP | PNG_FILTER_PAETH);
+     /* These will never be selected so we need not test them. */
+     filter_to_do &= ~(PNG_FILTER_UP | PNG_FILTER_PAETH);
   }
 #endif
 
@@ -2140,11 +2466,14 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
     * computationally expensive).
     *
     * GRR 980525:  consider also
+    *
     *   (1) minimum sum of absolute differences from running average (i.e.,
     *       keep running sum of non-absolute differences & count of bytes)
     *       [track dispersion, too?  restart average if dispersion too large?]
+    *
     *  (1b) minimum sum of absolute differences from sliding average, probably
     *       with window size <= deflate window (usually 32K)
+    *
     *   (2) minimum sum of squared differences from zero or running average
     *       (i.e., ~ root-mean-square approach)
     */
@@ -2153,12 +2482,11 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
    /* We don't need to test the 'no filter' case if this is the only filter
     * that has been chosen, as it doesn't actually do anything to the data.
     */
-   if ((filter_to_do & PNG_FILTER_NONE) &&
-       filter_to_do != PNG_FILTER_NONE)
+   if ((filter_to_do & PNG_FILTER_NONE) && filter_to_do != PNG_FILTER_NONE)
    {
       png_bytep rp;
       png_uint_32 sum = 0;
-      png_uint_32 i;
+      png_size_t i;
       int v;
 
       for (i = 0, rp = row_buf + 1; i < row_bytes; i++, rp++)
@@ -2181,9 +2509,10 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
             if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_NONE)
             {
                sumlo = (sumlo * png_ptr->filter_weights[j]) >>
-                  PNG_WEIGHT_SHIFT;
+                   PNG_WEIGHT_SHIFT;
+
                sumhi = (sumhi * png_ptr->filter_weights[j]) >>
-                  PNG_WEIGHT_SHIFT;
+                   PNG_WEIGHT_SHIFT;
             }
          }
 
@@ -2192,12 +2521,14 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
           * it has the minimum possible computational cost - none).
           */
          sumlo = (sumlo * png_ptr->filter_costs[PNG_FILTER_VALUE_NONE]) >>
-            PNG_COST_SHIFT;
+             PNG_COST_SHIFT;
+
          sumhi = (sumhi * png_ptr->filter_costs[PNG_FILTER_VALUE_NONE]) >>
-            PNG_COST_SHIFT;
+             PNG_COST_SHIFT;
 
          if (sumhi > PNG_HIMASK)
             sum = PNG_MAXSUM;
+
          else
             sum = (sumhi << PNG_HISHIFT) + sumlo;
       }
@@ -2210,17 +2541,20 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
    /* It's the only filter so no testing is needed */
    {
       png_bytep rp, lp, dp;
-      png_uint_32 i;
+      png_size_t i;
+
       for (i = 0, rp = row_buf + 1, dp = png_ptr->sub_row + 1; i < bpp;
            i++, rp++, dp++)
       {
          *dp = *rp;
       }
+
       for (lp = row_buf + 1; i < row_bytes;
          i++, rp++, lp++, dp++)
       {
          *dp = (png_byte)(((int)*rp - (int)*lp) & 0xff);
       }
+
       best_row = png_ptr->sub_row;
    }
 
@@ -2228,7 +2562,7 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
    {
       png_bytep rp, dp, lp;
       png_uint_32 sum = 0, lmins = mins;
-      png_uint_32 i;
+      png_size_t i;
       int v;
 
 #ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED
@@ -2248,19 +2582,22 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
             if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_SUB)
             {
                lmlo = (lmlo * png_ptr->inv_filter_weights[j]) >>
-                  PNG_WEIGHT_SHIFT;
+                   PNG_WEIGHT_SHIFT;
+
                lmhi = (lmhi * png_ptr->inv_filter_weights[j]) >>
-                  PNG_WEIGHT_SHIFT;
+                   PNG_WEIGHT_SHIFT;
             }
          }
 
          lmlo = (lmlo * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_SUB]) >>
-            PNG_COST_SHIFT;
+             PNG_COST_SHIFT;
+
          lmhi = (lmhi * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_SUB]) >>
-            PNG_COST_SHIFT;
+             PNG_COST_SHIFT;
 
          if (lmhi > PNG_HIMASK)
             lmins = PNG_MAXSUM;
+
          else
             lmins = (lmhi << PNG_HISHIFT) + lmlo;
       }
@@ -2273,6 +2610,7 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
 
          sum += (v < 128) ? v : 256 - v;
       }
+
       for (lp = row_buf + 1; i < row_bytes;
          i++, rp++, lp++, dp++)
       {
@@ -2297,19 +2635,22 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
             if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_SUB)
             {
                sumlo = (sumlo * png_ptr->inv_filter_weights[j]) >>
-                  PNG_WEIGHT_SHIFT;
+                   PNG_WEIGHT_SHIFT;
+
                sumhi = (sumhi * png_ptr->inv_filter_weights[j]) >>
-                  PNG_WEIGHT_SHIFT;
+                   PNG_WEIGHT_SHIFT;
             }
          }
 
          sumlo = (sumlo * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_SUB]) >>
-            PNG_COST_SHIFT;
+             PNG_COST_SHIFT;
+
          sumhi = (sumhi * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_SUB]) >>
-            PNG_COST_SHIFT;
+             PNG_COST_SHIFT;
 
          if (sumhi > PNG_HIMASK)
             sum = PNG_MAXSUM;
+
          else
             sum = (sumhi << PNG_HISHIFT) + sumlo;
       }
@@ -2326,14 +2667,15 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
    if (filter_to_do == PNG_FILTER_UP)
    {
       png_bytep rp, dp, pp;
-      png_uint_32 i;
+      png_size_t i;
 
       for (i = 0, rp = row_buf + 1, dp = png_ptr->up_row + 1,
-           pp = prev_row + 1; i < row_bytes;
-           i++, rp++, pp++, dp++)
+          pp = prev_row + 1; i < row_bytes;
+          i++, rp++, pp++, dp++)
       {
          *dp = (png_byte)(((int)*rp - (int)*pp) & 0xff);
       }
+
       best_row = png_ptr->up_row;
    }
 
@@ -2341,7 +2683,7 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
    {
       png_bytep rp, dp, pp;
       png_uint_32 sum = 0, lmins = mins;
-      png_uint_32 i;
+      png_size_t i;
       int v;
 
 
@@ -2358,26 +2700,29 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
             if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_UP)
             {
                lmlo = (lmlo * png_ptr->inv_filter_weights[j]) >>
-                  PNG_WEIGHT_SHIFT;
+                   PNG_WEIGHT_SHIFT;
+
                lmhi = (lmhi * png_ptr->inv_filter_weights[j]) >>
-                  PNG_WEIGHT_SHIFT;
+                   PNG_WEIGHT_SHIFT;
             }
          }
 
          lmlo = (lmlo * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_UP]) >>
-            PNG_COST_SHIFT;
+             PNG_COST_SHIFT;
+
          lmhi = (lmhi * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_UP]) >>
-            PNG_COST_SHIFT;
+             PNG_COST_SHIFT;
 
          if (lmhi > PNG_HIMASK)
             lmins = PNG_MAXSUM;
+
          else
             lmins = (lmhi << PNG_HISHIFT) + lmlo;
       }
 #endif
 
       for (i = 0, rp = row_buf + 1, dp = png_ptr->up_row + 1,
-           pp = prev_row + 1; i < row_bytes; i++)
+          pp = prev_row + 1; i < row_bytes; i++)
       {
          v = *dp++ = (png_byte)(((int)*rp++ - (int)*pp++) & 0xff);
 
@@ -2400,19 +2745,22 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
             if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_UP)
             {
                sumlo = (sumlo * png_ptr->filter_weights[j]) >>
-                  PNG_WEIGHT_SHIFT;
+                   PNG_WEIGHT_SHIFT;
+
                sumhi = (sumhi * png_ptr->filter_weights[j]) >>
-                  PNG_WEIGHT_SHIFT;
+                   PNG_WEIGHT_SHIFT;
             }
          }
 
          sumlo = (sumlo * png_ptr->filter_costs[PNG_FILTER_VALUE_UP]) >>
-            PNG_COST_SHIFT;
+             PNG_COST_SHIFT;
+
          sumhi = (sumhi * png_ptr->filter_costs[PNG_FILTER_VALUE_UP]) >>
-            PNG_COST_SHIFT;
+             PNG_COST_SHIFT;
 
          if (sumhi > PNG_HIMASK)
             sum = PNG_MAXSUM;
+
          else
             sum = (sumhi << PNG_HISHIFT) + sumlo;
       }
@@ -2430,11 +2778,13 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
    {
       png_bytep rp, dp, pp, lp;
       png_uint_32 i;
+
       for (i = 0, rp = row_buf + 1, dp = png_ptr->avg_row + 1,
            pp = prev_row + 1; i < bpp; i++)
       {
          *dp++ = (png_byte)(((int)*rp++ - ((int)*pp++ / 2)) & 0xff);
       }
+
       for (lp = row_buf + 1; i < row_bytes; i++)
       {
          *dp++ = (png_byte)(((int)*rp++ - (((int)*pp++ + (int)*lp++) / 2))
@@ -2447,7 +2797,7 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
    {
       png_bytep rp, dp, pp, lp;
       png_uint_32 sum = 0, lmins = mins;
-      png_uint_32 i;
+      png_size_t i;
       int v;
 
 #ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED
@@ -2463,19 +2813,22 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
             if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_AVG)
             {
                lmlo = (lmlo * png_ptr->inv_filter_weights[j]) >>
-                  PNG_WEIGHT_SHIFT;
+                   PNG_WEIGHT_SHIFT;
+
                lmhi = (lmhi * png_ptr->inv_filter_weights[j]) >>
-                  PNG_WEIGHT_SHIFT;
+                   PNG_WEIGHT_SHIFT;
             }
          }
 
          lmlo = (lmlo * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_AVG]) >>
-            PNG_COST_SHIFT;
+             PNG_COST_SHIFT;
+
          lmhi = (lmhi * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_AVG]) >>
-            PNG_COST_SHIFT;
+             PNG_COST_SHIFT;
 
          if (lmhi > PNG_HIMASK)
             lmins = PNG_MAXSUM;
+
          else
             lmins = (lmhi << PNG_HISHIFT) + lmlo;
       }
@@ -2488,10 +2841,11 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
 
          sum += (v < 128) ? v : 256 - v;
       }
+
       for (lp = row_buf + 1; i < row_bytes; i++)
       {
          v = *dp++ =
-          (png_byte)(((int)*rp++ - (((int)*pp++ + (int)*lp++) / 2)) & 0xff);
+             (png_byte)(((int)*rp++ - (((int)*pp++ + (int)*lp++) / 2)) & 0xff);
 
          sum += (v < 128) ? v : 256 - v;
 
@@ -2512,19 +2866,22 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
             if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_NONE)
             {
                sumlo = (sumlo * png_ptr->filter_weights[j]) >>
-                  PNG_WEIGHT_SHIFT;
+                   PNG_WEIGHT_SHIFT;
+
                sumhi = (sumhi * png_ptr->filter_weights[j]) >>
-                  PNG_WEIGHT_SHIFT;
+                   PNG_WEIGHT_SHIFT;
             }
          }
 
          sumlo = (sumlo * png_ptr->filter_costs[PNG_FILTER_VALUE_AVG]) >>
-            PNG_COST_SHIFT;
+             PNG_COST_SHIFT;
+
          sumhi = (sumhi * png_ptr->filter_costs[PNG_FILTER_VALUE_AVG]) >>
-            PNG_COST_SHIFT;
+             PNG_COST_SHIFT;
 
          if (sumhi > PNG_HIMASK)
             sum = PNG_MAXSUM;
+
          else
             sum = (sumhi << PNG_HISHIFT) + sumlo;
       }
@@ -2541,9 +2898,10 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
    if (filter_to_do == PNG_FILTER_PAETH)
    {
       png_bytep rp, dp, pp, cp, lp;
-      png_uint_32 i;
+      png_size_t i;
+
       for (i = 0, rp = row_buf + 1, dp = png_ptr->paeth_row + 1,
-           pp = prev_row + 1; i < bpp; i++)
+          pp = prev_row + 1; i < bpp; i++)
       {
          *dp++ = (png_byte)(((int)*rp++ - (int)*pp++) & 0xff);
       }
@@ -2580,7 +2938,7 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
    {
       png_bytep rp, dp, pp, cp, lp;
       png_uint_32 sum = 0, lmins = mins;
-      png_uint_32 i;
+      png_size_t i;
       int v;
 
 #ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED
@@ -2596,26 +2954,29 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
             if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_PAETH)
             {
                lmlo = (lmlo * png_ptr->inv_filter_weights[j]) >>
-                  PNG_WEIGHT_SHIFT;
+                   PNG_WEIGHT_SHIFT;
+
                lmhi = (lmhi * png_ptr->inv_filter_weights[j]) >>
-                  PNG_WEIGHT_SHIFT;
+                   PNG_WEIGHT_SHIFT;
             }
          }
 
          lmlo = (lmlo * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_PAETH]) >>
-            PNG_COST_SHIFT;
+             PNG_COST_SHIFT;
+
          lmhi = (lmhi * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_PAETH]) >>
-            PNG_COST_SHIFT;
+             PNG_COST_SHIFT;
 
          if (lmhi > PNG_HIMASK)
             lmins = PNG_MAXSUM;
+
          else
             lmins = (lmhi << PNG_HISHIFT) + lmlo;
       }
 #endif
 
       for (i = 0, rp = row_buf + 1, dp = png_ptr->paeth_row + 1,
-           pp = prev_row + 1; i < bpp; i++)
+          pp = prev_row + 1; i < bpp; i++)
       {
          v = *dp++ = (png_byte)(((int)*rp++ - (int)*pp++) & 0xff);
 
@@ -2648,10 +3009,13 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
          pa = abs(p - a);
          pb = abs(p - b);
          pc = abs(p - c);
+
          if (pa <= pb && pa <= pc)
             p = a;
+
          else if (pb <= pc)
             p = b;
+
          else
             p = c;
 #endif /* PNG_SLOW_PAETH */
@@ -2677,19 +3041,22 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
             if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_PAETH)
             {
                sumlo = (sumlo * png_ptr->filter_weights[j]) >>
-                  PNG_WEIGHT_SHIFT;
+                   PNG_WEIGHT_SHIFT;
+
                sumhi = (sumhi * png_ptr->filter_weights[j]) >>
-                  PNG_WEIGHT_SHIFT;
+                   PNG_WEIGHT_SHIFT;
             }
          }
 
          sumlo = (sumlo * png_ptr->filter_costs[PNG_FILTER_VALUE_PAETH]) >>
-            PNG_COST_SHIFT;
+             PNG_COST_SHIFT;
+
          sumhi = (sumhi * png_ptr->filter_costs[PNG_FILTER_VALUE_PAETH]) >>
-            PNG_COST_SHIFT;
+             PNG_COST_SHIFT;
 
          if (sumhi > PNG_HIMASK)
             sum = PNG_MAXSUM;
+
          else
             sum = (sumhi << PNG_HISHIFT) + sumlo;
       }
@@ -2701,9 +3068,9 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
       }
    }
 #endif /* PNG_WRITE_FILTER_SUPPORTED */
-   /* Do the actual writing of the filtered row data from the chosen filter. */
 
-   png_write_filtered_row(png_ptr, best_row);
+   /* Do the actual writing of the filtered row data from the chosen filter. */
+   png_write_filtered_row(png_ptr, best_row, row_info->rowbytes+1);
 
 #ifdef PNG_WRITE_FILTER_SUPPORTED
 #ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED
@@ -2711,10 +3078,12 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
    if (png_ptr->num_prev_filters > 0)
    {
       int j;
+
       for (j = 1; j < num_p_filters; j++)
       {
          png_ptr->prev_filters[j] = png_ptr->prev_filters[j - 1];
       }
+
       png_ptr->prev_filters[j] = best_row[0];
    }
 #endif
@@ -2723,8 +3092,9 @@ png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
 
 
 /* Do the actual writing of a previously filtered row. */
-void /* PRIVATE */
-png_write_filtered_row(png_structp png_ptr, png_bytep filtered_row)
+static void
+png_write_filtered_row(png_structp png_ptr, png_bytep filtered_row,
+   png_size_t avail/*includes filter byte*/)
 {
    png_debug(1, "in png_write_filtered_row");
 
@@ -2732,19 +3102,45 @@ png_write_filtered_row(png_structp png_ptr, png_bytep filtered_row)
    /* Set up the zlib input buffer */
 
    png_ptr->zstream.next_in = filtered_row;
-   png_ptr->zstream.avail_in = (uInt)png_ptr->row_info.rowbytes + 1;
+   png_ptr->zstream.avail_in = 0;
    /* Repeat until we have compressed all the data */
    do
    {
       int ret; /* Return of zlib */
 
+      /* Record the number of bytes available - zlib supports at least 65535
+       * bytes at one step, depending on the size of the zlib type 'uInt', the
+       * maximum size zlib can write at once is ZLIB_IO_MAX (from pngpriv.h).
+       * Use this because on 16 bit systems 'rowbytes' can be up to 65536 (i.e.
+       * one more than 16 bits) and, in this case 'rowbytes+1' can overflow a
+       * uInt.  ZLIB_IO_MAX can be safely reduced to cause zlib to be called
+       * with smaller chunks of data.
+       */
+      if (png_ptr->zstream.avail_in == 0)
+      {
+         if (avail > ZLIB_IO_MAX)
+         {
+            png_ptr->zstream.avail_in  = ZLIB_IO_MAX;
+            avail -= ZLIB_IO_MAX;
+         }
+
+         else
+         {
+            /* So this will fit in the available uInt space: */
+            png_ptr->zstream.avail_in = (uInt)avail;
+            avail = 0;
+         }
+      }
+
       /* Compress the data */
       ret = deflate(&png_ptr->zstream, Z_NO_FLUSH);
+
       /* Check for compression errors */
       if (ret != Z_OK)
       {
          if (png_ptr->zstream.msg != NULL)
             png_error(png_ptr, png_ptr->zstream.msg);
+
          else
             png_error(png_ptr, "zlib error");
       }
@@ -2754,11 +3150,9 @@ png_write_filtered_row(png_structp png_ptr, png_bytep filtered_row)
       {
          /* Write the IDAT and reset the zlib output buffer */
          png_write_IDAT(png_ptr, png_ptr->zbuf, png_ptr->zbuf_size);
-         png_ptr->zstream.next_out = png_ptr->zbuf;
-         png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
       }
    /* Repeat until all data has been compressed */
-   } while (png_ptr->zstream.avail_in);
+   } while (avail > 0 || png_ptr->zstream.avail_in > 0);
 
    /* Swap the current and previous rows */
    if (png_ptr->prev_row != NULL)