src/jpeg/jutils.c

   1 /*
   2  * jutils.c
   3  *
   4  * Copyright (C) 1991-1996, Thomas G. Lane.
   5  * This file is part of the Independent JPEG Group's software.
   6  * For conditions of distribution and use, see the accompanying README file.
   7  *
   8  * This file contains tables and miscellaneous utility routines needed
   9  * for both compression and decompression.
  10  * Note we prefix all global names with "j" to minimize conflicts with
  11  * a surrounding application.
  12  */
  13
  14 #define JPEG_INTERNALS
  15 #include "jinclude.h"
  16 #include "jpeglib.h"
  17
  18
  19 /*
  20  * jpeg_zigzag_order[i] is the zigzag-order position of the i'th element
  21  * of a DCT block read in natural order (left to right, top to bottom).
  22  */
  23
  24 #if 0                           /* This table is not actually needed in v6a */
  25
  26 const int jpeg_zigzag_order[DCTSIZE2] = {
  27    0,  1,  5,  6, 14, 15, 27, 28,
  28    2,  4,  7, 13, 16, 26, 29, 42,
  29    3,  8, 12, 17, 25, 30, 41, 43,
  30    9, 11, 18, 24, 31, 40, 44, 53,
  31   10, 19, 23, 32, 39, 45, 52, 54,
  32   20, 22, 33, 38, 46, 51, 55, 60,
  33   21, 34, 37, 47, 50, 56, 59, 61,
  34   35, 36, 48, 49, 57, 58, 62, 63
  35 };
  36
  37 #endif
  38
  39 /*
  40  * jpeg_natural_order[i] is the natural-order position of the i'th element
  41  * of zigzag order.
  42  *
  43  * When reading corrupted data, the Huffman decoders could attempt
  44  * to reference an entry beyond the end of this array (if the decoded
  45  * zero run length reaches past the end of the block).  To prevent
  46  * wild stores without adding an inner-loop test, we put some extra
  47  * "63"s after the real entries.  This will cause the extra coefficient
  48  * to be stored in location 63 of the block, not somewhere random.
  49  * The worst case would be a run-length of 15, which means we need 16
  50  * fake entries.
  51  */
  52
  53 const int jpeg_natural_order[DCTSIZE2+16] = {
  54   0,  1,  8, 16,  9,  2,  3, 10,
  55  17, 24, 32, 25, 18, 11,  4,  5,
  56  12, 19, 26, 33, 40, 48, 41, 34,
  57  27, 20, 13,  6,  7, 14, 21, 28,
  58  35, 42, 49, 56, 57, 50, 43, 36,
  59  29, 22, 15, 23, 30, 37, 44, 51,
  60  58, 59, 52, 45, 38, 31, 39, 46,
  61  53, 60, 61, 54, 47, 55, 62, 63,
  62  63, 63, 63, 63, 63, 63, 63, 63, /* extra entries for safety in decoder */
  63  63, 63, 63, 63, 63, 63, 63, 63
  64 };
  65
  66
  67 /*
  68  * Arithmetic utilities
  69  */
  70
  71 GLOBAL(long)
  72 jdiv_round_up (long a, long b)
  73 /* Compute a/b rounded up to next integer, ie, ceil(a/b) */
  74 /* Assumes a >= 0, b > 0 */
  75 {
  76   return (a + b - 1L) / b;
  77 }
  78
  79
  80 GLOBAL(long)
  81 jround_up (long a, long b)
  82 /* Compute a rounded up to next multiple of b, ie, ceil(a/b)*b */
  83 /* Assumes a >= 0, b > 0 */
  84 {
  85   a += b - 1L;
  86   return a - (a % b);
  87 }
  88
  89
  90 /* On normal machines we can apply MEMCOPY() and MEMZERO() to sample arrays
  91  * and coefficient-block arrays.  This won't work on 80x86 because the arrays
  92  * are FAR and we're assuming a small-pointer memory model.  However, some
  93  * DOS compilers provide far-pointer versions of memcpy() and memset() even
  94  * in the small-model libraries.  These will be used if USE_FMEM is defined.
  95  * Otherwise, the routines below do it the hard way.  (The performance cost
  96  * is not all that great, because these routines aren't very heavily used.)
  97  */
  98
  99 #ifndef NEED_FAR_POINTERS       /* normal case, same as regular macros */
 100 #define FMEMCOPY(dest,src,size) MEMCOPY(dest,src,size)
 101 #define FMEMZERO(target,size)   MEMZERO(target,size)
 102 #else                           /* 80x86 case, define if we can */
 103 #ifdef USE_FMEM
 104 #define FMEMCOPY(dest,src,size) _fmemcpy((void FAR *)(dest), (const void FAR *)(src), (size_t)(size))
 105 #define FMEMZERO(target,size)   _fmemset((void FAR *)(target), 0, (size_t)(size))
 106 #endif
 107 #endif
 108
 109
 110 GLOBAL(void)
 111 jcopy_sample_rows (JSAMPARRAY input_array, int source_row,
 112                    JSAMPARRAY output_array, int dest_row,
 113                    int num_rows, JDIMENSION num_cols)
 114 /* Copy some rows of samples from one place to another.
 115  * num_rows rows are copied from input_array[source_row++]
 116  * to output_array[dest_row++]; these areas may overlap for duplication.
 117  * The source and destination arrays must be at least as wide as num_cols.
 118  */
 119 {
 120   register JSAMPROW inptr, outptr;
 121 #ifdef FMEMCOPY
 122   register size_t count = (size_t) (num_cols * SIZEOF(JSAMPLE));
 123 #else
 124   register JDIMENSION count;
 125 #endif
 126   register int row;
 127
 128   input_array += source_row;
 129   output_array += dest_row;
 130
 131   for (row = num_rows; row > 0; row--) {
 132     inptr = *input_array++;
 133     outptr = *output_array++;
 134 #ifdef FMEMCOPY
 135     FMEMCOPY(outptr, inptr, count);
 136 #else
 137     for (count = num_cols; count > 0; count--)
 138       *outptr++ = *inptr++;     /* needn't bother with GETJSAMPLE() here */
 139 #endif
 140   }
 141 }
 142
 143
 144 GLOBAL(void)
 145 jcopy_block_row (JBLOCKROW input_row, JBLOCKROW output_row,
 146                  JDIMENSION num_blocks)
 147 /* Copy a row of coefficient blocks from one place to another. */
 148 {
 149 #ifdef FMEMCOPY
 150   FMEMCOPY(output_row, input_row, num_blocks * (DCTSIZE2 * SIZEOF(JCOEF)));
 151 #else
 152   register JCOEFPTR inptr, outptr;
 153   register long count;
 154
 155   inptr = (JCOEFPTR) input_row;
 156   outptr = (JCOEFPTR) output_row;
 157   for (count = (long) num_blocks * DCTSIZE2; count > 0; count--) {
 158     *outptr++ = *inptr++;
 159   }
 160 #endif
 161 }
 162
 163
 164 GLOBAL(void)
 165 jzero_far (void FAR * target, size_t bytestozero)
 166 /* Zero out a chunk of FAR memory. */
 167 /* This might be sample-array data, block-array data, or alloc_large data. */
 168 {
 169 #ifdef FMEMZERO
 170   FMEMZERO(target, bytestozero);
 171 #else
 172   register char FAR * ptr = (char FAR *) target;
 173   register size_t count;
 174
 175   for (count = bytestozero; count > 0; count--) {
 176     *ptr++ = 0;
 177   }
 178 #endif
 179 }