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annotate libs/libjpeg/jdct.h @ 3:dc735bdeeb8a

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author John Tsiombikas <nuclear@member.fsf.org>
date Mon, 21 Sep 2015 07:40:34 +0300
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nuclear@2 1 /*
nuclear@2 2 * jdct.h
nuclear@2 3 *
nuclear@2 4 * Copyright (C) 1994-1996, Thomas G. Lane.
nuclear@2 5 * This file is part of the Independent JPEG Group's software.
nuclear@2 6 * For conditions of distribution and use, see the accompanying README file.
nuclear@2 7 *
nuclear@2 8 * This include file contains common declarations for the forward and
nuclear@2 9 * inverse DCT modules. These declarations are private to the DCT managers
nuclear@2 10 * (jcdctmgr.c, jddctmgr.c) and the individual DCT algorithms.
nuclear@2 11 * The individual DCT algorithms are kept in separate files to ease
nuclear@2 12 * machine-dependent tuning (e.g., assembly coding).
nuclear@2 13 */
nuclear@2 14
nuclear@2 15
nuclear@2 16 /*
nuclear@2 17 * A forward DCT routine is given a pointer to a work area of type DCTELEM[];
nuclear@2 18 * the DCT is to be performed in-place in that buffer. Type DCTELEM is int
nuclear@2 19 * for 8-bit samples, INT32 for 12-bit samples. (NOTE: Floating-point DCT
nuclear@2 20 * implementations use an array of type FAST_FLOAT, instead.)
nuclear@2 21 * The DCT inputs are expected to be signed (range +-CENTERJSAMPLE).
nuclear@2 22 * The DCT outputs are returned scaled up by a factor of 8; they therefore
nuclear@2 23 * have a range of +-8K for 8-bit data, +-128K for 12-bit data. This
nuclear@2 24 * convention improves accuracy in integer implementations and saves some
nuclear@2 25 * work in floating-point ones.
nuclear@2 26 * Quantization of the output coefficients is done by jcdctmgr.c.
nuclear@2 27 */
nuclear@2 28
nuclear@2 29 #if BITS_IN_JSAMPLE == 8
nuclear@2 30 typedef int DCTELEM; /* 16 or 32 bits is fine */
nuclear@2 31 #else
nuclear@2 32 typedef INT32 DCTELEM; /* must have 32 bits */
nuclear@2 33 #endif
nuclear@2 34
nuclear@2 35 typedef JMETHOD(void, forward_DCT_method_ptr, (DCTELEM * data));
nuclear@2 36 typedef JMETHOD(void, float_DCT_method_ptr, (FAST_FLOAT * data));
nuclear@2 37
nuclear@2 38
nuclear@2 39 /*
nuclear@2 40 * An inverse DCT routine is given a pointer to the input JBLOCK and a pointer
nuclear@2 41 * to an output sample array. The routine must dequantize the input data as
nuclear@2 42 * well as perform the IDCT; for dequantization, it uses the multiplier table
nuclear@2 43 * pointed to by compptr->dct_table. The output data is to be placed into the
nuclear@2 44 * sample array starting at a specified column. (Any row offset needed will
nuclear@2 45 * be applied to the array pointer before it is passed to the IDCT code.)
nuclear@2 46 * Note that the number of samples emitted by the IDCT routine is
nuclear@2 47 * DCT_scaled_size * DCT_scaled_size.
nuclear@2 48 */
nuclear@2 49
nuclear@2 50 /* typedef inverse_DCT_method_ptr is declared in jpegint.h */
nuclear@2 51
nuclear@2 52 /*
nuclear@2 53 * Each IDCT routine has its own ideas about the best dct_table element type.
nuclear@2 54 */
nuclear@2 55
nuclear@2 56 typedef MULTIPLIER ISLOW_MULT_TYPE; /* short or int, whichever is faster */
nuclear@2 57 #if BITS_IN_JSAMPLE == 8
nuclear@2 58 typedef MULTIPLIER IFAST_MULT_TYPE; /* 16 bits is OK, use short if faster */
nuclear@2 59 #define IFAST_SCALE_BITS 2 /* fractional bits in scale factors */
nuclear@2 60 #else
nuclear@2 61 typedef INT32 IFAST_MULT_TYPE; /* need 32 bits for scaled quantizers */
nuclear@2 62 #define IFAST_SCALE_BITS 13 /* fractional bits in scale factors */
nuclear@2 63 #endif
nuclear@2 64 typedef FAST_FLOAT FLOAT_MULT_TYPE; /* preferred floating type */
nuclear@2 65
nuclear@2 66
nuclear@2 67 /*
nuclear@2 68 * Each IDCT routine is responsible for range-limiting its results and
nuclear@2 69 * converting them to unsigned form (0..MAXJSAMPLE). The raw outputs could
nuclear@2 70 * be quite far out of range if the input data is corrupt, so a bulletproof
nuclear@2 71 * range-limiting step is required. We use a mask-and-table-lookup method
nuclear@2 72 * to do the combined operations quickly. See the comments with
nuclear@2 73 * prepare_range_limit_table (in jdmaster.c) for more info.
nuclear@2 74 */
nuclear@2 75
nuclear@2 76 #define IDCT_range_limit(cinfo) ((cinfo)->sample_range_limit + CENTERJSAMPLE)
nuclear@2 77
nuclear@2 78 #define RANGE_MASK (MAXJSAMPLE * 4 + 3) /* 2 bits wider than legal samples */
nuclear@2 79
nuclear@2 80
nuclear@2 81 /* Short forms of external names for systems with brain-damaged linkers. */
nuclear@2 82
nuclear@2 83 #ifdef NEED_SHORT_EXTERNAL_NAMES
nuclear@2 84 #define jpeg_fdct_islow jFDislow
nuclear@2 85 #define jpeg_fdct_ifast jFDifast
nuclear@2 86 #define jpeg_fdct_float jFDfloat
nuclear@2 87 #define jpeg_idct_islow jRDislow
nuclear@2 88 #define jpeg_idct_ifast jRDifast
nuclear@2 89 #define jpeg_idct_float jRDfloat
nuclear@2 90 #define jpeg_idct_4x4 jRD4x4
nuclear@2 91 #define jpeg_idct_2x2 jRD2x2
nuclear@2 92 #define jpeg_idct_1x1 jRD1x1
nuclear@2 93 #endif /* NEED_SHORT_EXTERNAL_NAMES */
nuclear@2 94
nuclear@2 95 /* Extern declarations for the forward and inverse DCT routines. */
nuclear@2 96
nuclear@2 97 EXTERN(void) jpeg_fdct_islow JPP((DCTELEM * data));
nuclear@2 98 EXTERN(void) jpeg_fdct_ifast JPP((DCTELEM * data));
nuclear@2 99 EXTERN(void) jpeg_fdct_float JPP((FAST_FLOAT * data));
nuclear@2 100
nuclear@2 101 EXTERN(void) jpeg_idct_islow
nuclear@2 102 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
nuclear@2 103 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
nuclear@2 104 EXTERN(void) jpeg_idct_ifast
nuclear@2 105 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
nuclear@2 106 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
nuclear@2 107 EXTERN(void) jpeg_idct_float
nuclear@2 108 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
nuclear@2 109 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
nuclear@2 110 EXTERN(void) jpeg_idct_4x4
nuclear@2 111 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
nuclear@2 112 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
nuclear@2 113 EXTERN(void) jpeg_idct_2x2
nuclear@2 114 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
nuclear@2 115 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
nuclear@2 116 EXTERN(void) jpeg_idct_1x1
nuclear@2 117 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
nuclear@2 118 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
nuclear@2 119
nuclear@2 120
nuclear@2 121 /*
nuclear@2 122 * Macros for handling fixed-point arithmetic; these are used by many
nuclear@2 123 * but not all of the DCT/IDCT modules.
nuclear@2 124 *
nuclear@2 125 * All values are expected to be of type INT32.
nuclear@2 126 * Fractional constants are scaled left by CONST_BITS bits.
nuclear@2 127 * CONST_BITS is defined within each module using these macros,
nuclear@2 128 * and may differ from one module to the next.
nuclear@2 129 */
nuclear@2 130
nuclear@2 131 #define ONE ((INT32) 1)
nuclear@2 132 #define CONST_SCALE (ONE << CONST_BITS)
nuclear@2 133
nuclear@2 134 /* Convert a positive real constant to an integer scaled by CONST_SCALE.
nuclear@2 135 * Caution: some C compilers fail to reduce "FIX(constant)" at compile time,
nuclear@2 136 * thus causing a lot of useless floating-point operations at run time.
nuclear@2 137 */
nuclear@2 138
nuclear@2 139 #define FIX(x) ((INT32) ((x) * CONST_SCALE + 0.5))
nuclear@2 140
nuclear@2 141 /* Descale and correctly round an INT32 value that's scaled by N bits.
nuclear@2 142 * We assume RIGHT_SHIFT rounds towards minus infinity, so adding
nuclear@2 143 * the fudge factor is correct for either sign of X.
nuclear@2 144 */
nuclear@2 145
nuclear@2 146 #define DESCALE(x,n) RIGHT_SHIFT((x) + (ONE << ((n)-1)), n)
nuclear@2 147
nuclear@2 148 /* Multiply an INT32 variable by an INT32 constant to yield an INT32 result.
nuclear@2 149 * This macro is used only when the two inputs will actually be no more than
nuclear@2 150 * 16 bits wide, so that a 16x16->32 bit multiply can be used instead of a
nuclear@2 151 * full 32x32 multiply. This provides a useful speedup on many machines.
nuclear@2 152 * Unfortunately there is no way to specify a 16x16->32 multiply portably
nuclear@2 153 * in C, but some C compilers will do the right thing if you provide the
nuclear@2 154 * correct combination of casts.
nuclear@2 155 */
nuclear@2 156
nuclear@2 157 #ifdef SHORTxSHORT_32 /* may work if 'int' is 32 bits */
nuclear@2 158 #define MULTIPLY16C16(var,const) (((INT16) (var)) * ((INT16) (const)))
nuclear@2 159 #endif
nuclear@2 160 #ifdef SHORTxLCONST_32 /* known to work with Microsoft C 6.0 */
nuclear@2 161 #define MULTIPLY16C16(var,const) (((INT16) (var)) * ((INT32) (const)))
nuclear@2 162 #endif
nuclear@2 163
nuclear@2 164 #ifndef MULTIPLY16C16 /* default definition */
nuclear@2 165 #define MULTIPLY16C16(var,const) ((var) * (const))
nuclear@2 166 #endif
nuclear@2 167
nuclear@2 168 /* Same except both inputs are variables. */
nuclear@2 169
nuclear@2 170 #ifdef SHORTxSHORT_32 /* may work if 'int' is 32 bits */
nuclear@2 171 #define MULTIPLY16V16(var1,var2) (((INT16) (var1)) * ((INT16) (var2)))
nuclear@2 172 #endif
nuclear@2 173
nuclear@2 174 #ifndef MULTIPLY16V16 /* default definition */
nuclear@2 175 #define MULTIPLY16V16(var1,var2) ((var1) * (var2))
nuclear@2 176 #endif