src/jpeg/jdct.h

   1 /*
   2  * jdct.h
   3  *
   4  * Copyright (C) 1994-1996, 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 include file contains common declarations for the forward and
   9  * inverse DCT modules.  These declarations are private to the DCT managers
  10  * (jcdctmgr.c, jddctmgr.c) and the individual DCT algorithms.
  11  * The individual DCT algorithms are kept in separate files to ease
  12  * machine-dependent tuning (e.g., assembly coding).
  13  */
  14
  15
  16 /*
  17  * A forward DCT routine is given a pointer to a work area of type DCTELEM[];
  18  * the DCT is to be performed in-place in that buffer.  Type DCTELEM is int
  19  * for 8-bit samples, INT32 for 12-bit samples.  (NOTE: Floating-point DCT
  20  * implementations use an array of type FAST_FLOAT, instead.)
  21  * The DCT inputs are expected to be signed (range +-CENTERJSAMPLE).
  22  * The DCT outputs are returned scaled up by a factor of 8; they therefore
  23  * have a range of +-8K for 8-bit data, +-128K for 12-bit data.  This
  24  * convention improves accuracy in integer implementations and saves some
  25  * work in floating-point ones.
  26  * Quantization of the output coefficients is done by jcdctmgr.c.
  27  */
  28
  29 #if BITS_IN_JSAMPLE == 8
  30 typedef int DCTELEM;            /* 16 or 32 bits is fine */
  31 #else
  32 typedef INT32 DCTELEM;          /* must have 32 bits */
  33 #endif
  34
  35 typedef JMETHOD(void, forward_DCT_method_ptr, (DCTELEM * data));
  36 typedef JMETHOD(void, float_DCT_method_ptr, (FAST_FLOAT * data));
  37
  38
  39 /*
  40  * An inverse DCT routine is given a pointer to the input JBLOCK and a pointer
  41  * to an output sample array.  The routine must dequantize the input data as
  42  * well as perform the IDCT; for dequantization, it uses the multiplier table
  43  * pointed to by compptr->dct_table.  The output data is to be placed into the
  44  * sample array starting at a specified column.  (Any row offset needed will
  45  * be applied to the array pointer before it is passed to the IDCT code.)
  46  * Note that the number of samples emitted by the IDCT routine is
  47  * DCT_scaled_size * DCT_scaled_size.
  48  */
  49
  50 /* typedef inverse_DCT_method_ptr is declared in jpegint.h */
  51
  52 /*
  53  * Each IDCT routine has its own ideas about the best dct_table element type.
  54  */
  55
  56 typedef MULTIPLIER ISLOW_MULT_TYPE; /* short or int, whichever is faster */
  57 #if BITS_IN_JSAMPLE == 8
  58 typedef MULTIPLIER IFAST_MULT_TYPE; /* 16 bits is OK, use short if faster */
  59 #define IFAST_SCALE_BITS  2     /* fractional bits in scale factors */
  60 #else
  61 typedef INT32 IFAST_MULT_TYPE;  /* need 32 bits for scaled quantizers */
  62 #define IFAST_SCALE_BITS  13    /* fractional bits in scale factors */
  63 #endif
  64 typedef FAST_FLOAT FLOAT_MULT_TYPE; /* preferred floating type */
  65
  66
  67 /*
  68  * Each IDCT routine is responsible for range-limiting its results and
  69  * converting them to unsigned form (0..MAXJSAMPLE).  The raw outputs could
  70  * be quite far out of range if the input data is corrupt, so a bulletproof
  71  * range-limiting step is required.  We use a mask-and-table-lookup method
  72  * to do the combined operations quickly.  See the comments with
  73  * prepare_range_limit_table (in jdmaster.c) for more info.
  74  */
  75
  76 #define IDCT_range_limit(cinfo)  ((cinfo)->sample_range_limit + CENTERJSAMPLE)
  77
  78 #define RANGE_MASK  (MAXJSAMPLE * 4 + 3) /* 2 bits wider than legal samples */
  79
  80
  81 /* Short forms of external names for systems with brain-damaged linkers. */
  82
  83 #ifdef NEED_SHORT_EXTERNAL_NAMES
  84 #define jpeg_fdct_islow         jFDislow
  85 #define jpeg_fdct_ifast         jFDifast
  86 #define jpeg_fdct_float         jFDfloat
  87 #define jpeg_idct_islow         jRDislow
  88 #define jpeg_idct_ifast         jRDifast
  89 #define jpeg_idct_float         jRDfloat
  90 #define jpeg_idct_4x4           jRD4x4
  91 #define jpeg_idct_2x2           jRD2x2
  92 #define jpeg_idct_1x1           jRD1x1
  93 #endif /* NEED_SHORT_EXTERNAL_NAMES */
  94
  95 /* Extern declarations for the forward and inverse DCT routines. */
  96
  97 EXTERN(void) jpeg_fdct_islow JPP((DCTELEM * data));
  98 EXTERN(void) jpeg_fdct_ifast JPP((DCTELEM * data));
  99 EXTERN(void) jpeg_fdct_float JPP((FAST_FLOAT * data));
 100
 101 EXTERN(void) jpeg_idct_islow
 102     JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
 103          JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
 104 EXTERN(void) jpeg_idct_ifast
 105     JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
 106          JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
 107 EXTERN(void) jpeg_idct_float
 108     JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
 109          JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
 110 EXTERN(void) jpeg_idct_4x4
 111     JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
 112          JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
 113 EXTERN(void) jpeg_idct_2x2
 114     JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
 115          JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
 116 EXTERN(void) jpeg_idct_1x1
 117     JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
 118          JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
 119
 120
 121 /*
 122  * Macros for handling fixed-point arithmetic; these are used by many
 123  * but not all of the DCT/IDCT modules.
 124  *
 125  * All values are expected to be of type INT32.
 126  * Fractional constants are scaled left by CONST_BITS bits.
 127  * CONST_BITS is defined within each module using these macros,
 128  * and may differ from one module to the next.
 129  */
 130
 131 #define ONE     ((INT32) 1)
 132 #define CONST_SCALE (ONE << CONST_BITS)
 133
 134 /* Convert a positive real constant to an integer scaled by CONST_SCALE.
 135  * Caution: some C compilers fail to reduce "FIX(constant)" at compile time,
 136  * thus causing a lot of useless floating-point operations at run time.
 137  */
 138
 139 #define FIX(x)  ((INT32) ((x) * CONST_SCALE + 0.5))
 140
 141 /* Descale and correctly round an INT32 value that's scaled by N bits.
 142  * We assume RIGHT_SHIFT rounds towards minus infinity, so adding
 143  * the fudge factor is correct for either sign of X.
 144  */
 145
 146 #define DESCALE(x,n)  RIGHT_SHIFT((x) + (ONE << ((n)-1)), n)
 147
 148 /* Multiply an INT32 variable by an INT32 constant to yield an INT32 result.
 149  * This macro is used only when the two inputs will actually be no more than
 150  * 16 bits wide, so that a 16x16->32 bit multiply can be used instead of a
 151  * full 32x32 multiply.  This provides a useful speedup on many machines.
 152  * Unfortunately there is no way to specify a 16x16->32 multiply portably
 153  * in C, but some C compilers will do the right thing if you provide the
 154  * correct combination of casts.
 155  */
 156
 157 #ifdef SHORTxSHORT_32           /* may work if 'int' is 32 bits */
 158 #define MULTIPLY16C16(var,const)  (((INT16) (var)) * ((INT16) (const)))
 159 #endif
 160 #ifdef SHORTxLCONST_32          /* known to work with Microsoft C 6.0 */
 161 #define MULTIPLY16C16(var,const)  (((INT16) (var)) * ((INT32) (const)))
 162 #endif
 163
 164 #ifndef MULTIPLY16C16           /* default definition */
 165 #define MULTIPLY16C16(var,const)  ((var) * (const))
 166 #endif
 167
 168 /* Same except both inputs are variables. */
 169
 170 #ifdef SHORTxSHORT_32           /* may work if 'int' is 32 bits */
 171 #define MULTIPLY16V16(var1,var2)  (((INT16) (var1)) * ((INT16) (var2)))
 172 #endif
 173
 174 #ifndef MULTIPLY16V16           /* default definition */
 175 #define MULTIPLY16V16(var1,var2)  ((var1) * (var2))
 176 #endif