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annotate libs/libjpeg/jdct.h @ 43:73813c1176de

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author John Tsiombikas <nuclear@member.fsf.org>
date Fri, 14 Aug 2015 04:33:42 +0300
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nuclear@26 1 /*
nuclear@26 2 * jdct.h
nuclear@26 3 *
nuclear@26 4 * Copyright (C) 1994-1996, Thomas G. Lane.
nuclear@26 5 * This file is part of the Independent JPEG Group's software.
nuclear@26 6 * For conditions of distribution and use, see the accompanying README file.
nuclear@26 7 *
nuclear@26 8 * This include file contains common declarations for the forward and
nuclear@26 9 * inverse DCT modules. These declarations are private to the DCT managers
nuclear@26 10 * (jcdctmgr.c, jddctmgr.c) and the individual DCT algorithms.
nuclear@26 11 * The individual DCT algorithms are kept in separate files to ease
nuclear@26 12 * machine-dependent tuning (e.g., assembly coding).
nuclear@26 13 */
nuclear@26 14
nuclear@26 15
nuclear@26 16 /*
nuclear@26 17 * A forward DCT routine is given a pointer to a work area of type DCTELEM[];
nuclear@26 18 * the DCT is to be performed in-place in that buffer. Type DCTELEM is int
nuclear@26 19 * for 8-bit samples, INT32 for 12-bit samples. (NOTE: Floating-point DCT
nuclear@26 20 * implementations use an array of type FAST_FLOAT, instead.)
nuclear@26 21 * The DCT inputs are expected to be signed (range +-CENTERJSAMPLE).
nuclear@26 22 * The DCT outputs are returned scaled up by a factor of 8; they therefore
nuclear@26 23 * have a range of +-8K for 8-bit data, +-128K for 12-bit data. This
nuclear@26 24 * convention improves accuracy in integer implementations and saves some
nuclear@26 25 * work in floating-point ones.
nuclear@26 26 * Quantization of the output coefficients is done by jcdctmgr.c.
nuclear@26 27 */
nuclear@26 28
nuclear@26 29 #if BITS_IN_JSAMPLE == 8
nuclear@26 30 typedef int DCTELEM; /* 16 or 32 bits is fine */
nuclear@26 31 #else
nuclear@26 32 typedef INT32 DCTELEM; /* must have 32 bits */
nuclear@26 33 #endif
nuclear@26 34
nuclear@26 35 typedef JMETHOD(void, forward_DCT_method_ptr, (DCTELEM * data));
nuclear@26 36 typedef JMETHOD(void, float_DCT_method_ptr, (FAST_FLOAT * data));
nuclear@26 37
nuclear@26 38
nuclear@26 39 /*
nuclear@26 40 * An inverse DCT routine is given a pointer to the input JBLOCK and a pointer
nuclear@26 41 * to an output sample array. The routine must dequantize the input data as
nuclear@26 42 * well as perform the IDCT; for dequantization, it uses the multiplier table
nuclear@26 43 * pointed to by compptr->dct_table. The output data is to be placed into the
nuclear@26 44 * sample array starting at a specified column. (Any row offset needed will
nuclear@26 45 * be applied to the array pointer before it is passed to the IDCT code.)
nuclear@26 46 * Note that the number of samples emitted by the IDCT routine is
nuclear@26 47 * DCT_scaled_size * DCT_scaled_size.
nuclear@26 48 */
nuclear@26 49
nuclear@26 50 /* typedef inverse_DCT_method_ptr is declared in jpegint.h */
nuclear@26 51
nuclear@26 52 /*
nuclear@26 53 * Each IDCT routine has its own ideas about the best dct_table element type.
nuclear@26 54 */
nuclear@26 55
nuclear@26 56 typedef MULTIPLIER ISLOW_MULT_TYPE; /* short or int, whichever is faster */
nuclear@26 57 #if BITS_IN_JSAMPLE == 8
nuclear@26 58 typedef MULTIPLIER IFAST_MULT_TYPE; /* 16 bits is OK, use short if faster */
nuclear@26 59 #define IFAST_SCALE_BITS 2 /* fractional bits in scale factors */
nuclear@26 60 #else
nuclear@26 61 typedef INT32 IFAST_MULT_TYPE; /* need 32 bits for scaled quantizers */
nuclear@26 62 #define IFAST_SCALE_BITS 13 /* fractional bits in scale factors */
nuclear@26 63 #endif
nuclear@26 64 typedef FAST_FLOAT FLOAT_MULT_TYPE; /* preferred floating type */
nuclear@26 65
nuclear@26 66
nuclear@26 67 /*
nuclear@26 68 * Each IDCT routine is responsible for range-limiting its results and
nuclear@26 69 * converting them to unsigned form (0..MAXJSAMPLE). The raw outputs could
nuclear@26 70 * be quite far out of range if the input data is corrupt, so a bulletproof
nuclear@26 71 * range-limiting step is required. We use a mask-and-table-lookup method
nuclear@26 72 * to do the combined operations quickly. See the comments with
nuclear@26 73 * prepare_range_limit_table (in jdmaster.c) for more info.
nuclear@26 74 */
nuclear@26 75
nuclear@26 76 #define IDCT_range_limit(cinfo) ((cinfo)->sample_range_limit + CENTERJSAMPLE)
nuclear@26 77
nuclear@26 78 #define RANGE_MASK (MAXJSAMPLE * 4 + 3) /* 2 bits wider than legal samples */
nuclear@26 79
nuclear@26 80
nuclear@26 81 /* Short forms of external names for systems with brain-damaged linkers. */
nuclear@26 82
nuclear@26 83 #ifdef NEED_SHORT_EXTERNAL_NAMES
nuclear@26 84 #define jpeg_fdct_islow jFDislow
nuclear@26 85 #define jpeg_fdct_ifast jFDifast
nuclear@26 86 #define jpeg_fdct_float jFDfloat
nuclear@26 87 #define jpeg_idct_islow jRDislow
nuclear@26 88 #define jpeg_idct_ifast jRDifast
nuclear@26 89 #define jpeg_idct_float jRDfloat
nuclear@26 90 #define jpeg_idct_4x4 jRD4x4
nuclear@26 91 #define jpeg_idct_2x2 jRD2x2
nuclear@26 92 #define jpeg_idct_1x1 jRD1x1
nuclear@26 93 #endif /* NEED_SHORT_EXTERNAL_NAMES */
nuclear@26 94
nuclear@26 95 /* Extern declarations for the forward and inverse DCT routines. */
nuclear@26 96
nuclear@26 97 EXTERN(void) jpeg_fdct_islow JPP((DCTELEM * data));
nuclear@26 98 EXTERN(void) jpeg_fdct_ifast JPP((DCTELEM * data));
nuclear@26 99 EXTERN(void) jpeg_fdct_float JPP((FAST_FLOAT * data));
nuclear@26 100
nuclear@26 101 EXTERN(void) jpeg_idct_islow
nuclear@26 102 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
nuclear@26 103 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
nuclear@26 104 EXTERN(void) jpeg_idct_ifast
nuclear@26 105 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
nuclear@26 106 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
nuclear@26 107 EXTERN(void) jpeg_idct_float
nuclear@26 108 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
nuclear@26 109 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
nuclear@26 110 EXTERN(void) jpeg_idct_4x4
nuclear@26 111 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
nuclear@26 112 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
nuclear@26 113 EXTERN(void) jpeg_idct_2x2
nuclear@26 114 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
nuclear@26 115 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
nuclear@26 116 EXTERN(void) jpeg_idct_1x1
nuclear@26 117 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
nuclear@26 118 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
nuclear@26 119
nuclear@26 120
nuclear@26 121 /*
nuclear@26 122 * Macros for handling fixed-point arithmetic; these are used by many
nuclear@26 123 * but not all of the DCT/IDCT modules.
nuclear@26 124 *
nuclear@26 125 * All values are expected to be of type INT32.
nuclear@26 126 * Fractional constants are scaled left by CONST_BITS bits.
nuclear@26 127 * CONST_BITS is defined within each module using these macros,
nuclear@26 128 * and may differ from one module to the next.
nuclear@26 129 */
nuclear@26 130
nuclear@26 131 #define ONE ((INT32) 1)
nuclear@26 132 #define CONST_SCALE (ONE << CONST_BITS)
nuclear@26 133
nuclear@26 134 /* Convert a positive real constant to an integer scaled by CONST_SCALE.
nuclear@26 135 * Caution: some C compilers fail to reduce "FIX(constant)" at compile time,
nuclear@26 136 * thus causing a lot of useless floating-point operations at run time.
nuclear@26 137 */
nuclear@26 138
nuclear@26 139 #define FIX(x) ((INT32) ((x) * CONST_SCALE + 0.5))
nuclear@26 140
nuclear@26 141 /* Descale and correctly round an INT32 value that's scaled by N bits.
nuclear@26 142 * We assume RIGHT_SHIFT rounds towards minus infinity, so adding
nuclear@26 143 * the fudge factor is correct for either sign of X.
nuclear@26 144 */
nuclear@26 145
nuclear@26 146 #define DESCALE(x,n) RIGHT_SHIFT((x) + (ONE << ((n)-1)), n)
nuclear@26 147
nuclear@26 148 /* Multiply an INT32 variable by an INT32 constant to yield an INT32 result.
nuclear@26 149 * This macro is used only when the two inputs will actually be no more than
nuclear@26 150 * 16 bits wide, so that a 16x16->32 bit multiply can be used instead of a
nuclear@26 151 * full 32x32 multiply. This provides a useful speedup on many machines.
nuclear@26 152 * Unfortunately there is no way to specify a 16x16->32 multiply portably
nuclear@26 153 * in C, but some C compilers will do the right thing if you provide the
nuclear@26 154 * correct combination of casts.
nuclear@26 155 */
nuclear@26 156
nuclear@26 157 #ifdef SHORTxSHORT_32 /* may work if 'int' is 32 bits */
nuclear@26 158 #define MULTIPLY16C16(var,const) (((INT16) (var)) * ((INT16) (const)))
nuclear@26 159 #endif
nuclear@26 160 #ifdef SHORTxLCONST_32 /* known to work with Microsoft C 6.0 */
nuclear@26 161 #define MULTIPLY16C16(var,const) (((INT16) (var)) * ((INT32) (const)))
nuclear@26 162 #endif
nuclear@26 163
nuclear@26 164 #ifndef MULTIPLY16C16 /* default definition */
nuclear@26 165 #define MULTIPLY16C16(var,const) ((var) * (const))
nuclear@26 166 #endif
nuclear@26 167
nuclear@26 168 /* Same except both inputs are variables. */
nuclear@26 169
nuclear@26 170 #ifdef SHORTxSHORT_32 /* may work if 'int' is 32 bits */
nuclear@26 171 #define MULTIPLY16V16(var1,var2) (((INT16) (var1)) * ((INT16) (var2)))
nuclear@26 172 #endif
nuclear@26 173
nuclear@26 174 #ifndef MULTIPLY16V16 /* default definition */
nuclear@26 175 #define MULTIPLY16V16(var1,var2) ((var1) * (var2))
nuclear@26 176 #endif