1 /* 2 * reserved comment block 3 * DO NOT REMOVE OR ALTER! 4 */ 5 /* 6 * jdct.h 7 * 8 * Copyright (C) 1994-1996, Thomas G. Lane. 9 * This file is part of the Independent JPEG Group's software. 10 * For conditions of distribution and use, see the accompanying README file. 11 * 12 * This include file contains common declarations for the forward and 13 * inverse DCT modules. These declarations are private to the DCT managers 14 * (jcdctmgr.c, jddctmgr.c) and the individual DCT algorithms. 15 * The individual DCT algorithms are kept in separate files to ease 16 * machine-dependent tuning (e.g., assembly coding). 17 */ 18 19 20 /* 21 * A forward DCT routine is given a pointer to a work area of type DCTELEM[]; 22 * the DCT is to be performed in-place in that buffer. Type DCTELEM is int 23 * for 8-bit samples, INT32 for 12-bit samples. (NOTE: Floating-point DCT 24 * implementations use an array of type FAST_FLOAT, instead.) 25 * The DCT inputs are expected to be signed (range +-CENTERJSAMPLE). 26 * The DCT outputs are returned scaled up by a factor of 8; they therefore 27 * have a range of +-8K for 8-bit data, +-128K for 12-bit data. This 28 * convention improves accuracy in integer implementations and saves some 29 * work in floating-point ones. 30 * Quantization of the output coefficients is done by jcdctmgr.c. 31 */ 32 33 #if BITS_IN_JSAMPLE == 8 34 typedef int DCTELEM; /* 16 or 32 bits is fine */ 35 #else 36 typedef INT32 DCTELEM; /* must have 32 bits */ 37 #endif 38 39 typedef JMETHOD(void, forward_DCT_method_ptr, (DCTELEM * data)); 40 typedef JMETHOD(void, float_DCT_method_ptr, (FAST_FLOAT * data)); 41 42 43 /* 44 * An inverse DCT routine is given a pointer to the input JBLOCK and a pointer 45 * to an output sample array. The routine must dequantize the input data as 46 * well as perform the IDCT; for dequantization, it uses the multiplier table 47 * pointed to by compptr->dct_table. The output data is to be placed into the 48 * sample array starting at a specified column. (Any row offset needed will 49 * be applied to the array pointer before it is passed to the IDCT code.) 50 * Note that the number of samples emitted by the IDCT routine is 51 * DCT_scaled_size * DCT_scaled_size. 52 */ 53 54 /* typedef inverse_DCT_method_ptr is declared in jpegint.h */ 55 56 /* 57 * Each IDCT routine has its own ideas about the best dct_table element type. 58 */ 59 60 typedef MULTIPLIER ISLOW_MULT_TYPE; /* short or int, whichever is faster */ 61 #if BITS_IN_JSAMPLE == 8 62 typedef MULTIPLIER IFAST_MULT_TYPE; /* 16 bits is OK, use short if faster */ 63 #define IFAST_SCALE_BITS 2 /* fractional bits in scale factors */ 64 #else 65 typedef INT32 IFAST_MULT_TYPE; /* need 32 bits for scaled quantizers */ 66 #define IFAST_SCALE_BITS 13 /* fractional bits in scale factors */ 67 #endif 68 typedef FAST_FLOAT FLOAT_MULT_TYPE; /* preferred floating type */ 69 70 71 /* 72 * Each IDCT routine is responsible for range-limiting its results and 73 * converting them to unsigned form (0..MAXJSAMPLE). The raw outputs could 74 * be quite far out of range if the input data is corrupt, so a bulletproof 75 * range-limiting step is required. We use a mask-and-table-lookup method 76 * to do the combined operations quickly. See the comments with 77 * prepare_range_limit_table (in jdmaster.c) for more info. 78 */ 79 80 #define IDCT_range_limit(cinfo) ((cinfo)->sample_range_limit + CENTERJSAMPLE) 81 82 #define RANGE_MASK (MAXJSAMPLE * 4 + 3) /* 2 bits wider than legal samples */ 83 84 85 /* Short forms of external names for systems with brain-damaged linkers. */ 86 87 #ifdef NEED_SHORT_EXTERNAL_NAMES 88 #define jpeg_fdct_islow jFDislow 89 #define jpeg_fdct_ifast jFDifast 90 #define jpeg_fdct_float jFDfloat 91 #define jpeg_idct_islow jRDislow 92 #define jpeg_idct_ifast jRDifast 93 #define jpeg_idct_float jRDfloat 94 #define jpeg_idct_4x4 jRD4x4 95 #define jpeg_idct_2x2 jRD2x2 96 #define jpeg_idct_1x1 jRD1x1 97 #endif /* NEED_SHORT_EXTERNAL_NAMES */ 98 99 /* Extern declarations for the forward and inverse DCT routines. */ 100 101 EXTERN(void) jpeg_fdct_islow JPP((DCTELEM * data)); 102 EXTERN(void) jpeg_fdct_ifast JPP((DCTELEM * data)); 103 EXTERN(void) jpeg_fdct_float JPP((FAST_FLOAT * data)); 104 105 EXTERN(void) jpeg_idct_islow 106 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, 107 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); 108 EXTERN(void) jpeg_idct_ifast 109 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, 110 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); 111 EXTERN(void) jpeg_idct_float 112 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, 113 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); 114 EXTERN(void) jpeg_idct_4x4 115 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, 116 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); 117 EXTERN(void) jpeg_idct_2x2 118 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, 119 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); 120 EXTERN(void) jpeg_idct_1x1 121 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, 122 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); 123 124 125 /* 126 * Macros for handling fixed-point arithmetic; these are used by many 127 * but not all of the DCT/IDCT modules. 128 * 129 * All values are expected to be of type INT32. 130 * Fractional constants are scaled left by CONST_BITS bits. 131 * CONST_BITS is defined within each module using these macros, 132 * and may differ from one module to the next. 133 */ 134 135 #define ONE ((INT32) 1) 136 #define CONST_SCALE (ONE << CONST_BITS) 137 138 /* Convert a positive real constant to an integer scaled by CONST_SCALE. 139 * Caution: some C compilers fail to reduce "FIX(constant)" at compile time, 140 * thus causing a lot of useless floating-point operations at run time. 141 */ 142 143 #define FIX(x) ((INT32) ((x) * CONST_SCALE + 0.5)) 144 145 /* Descale and correctly round an INT32 value that's scaled by N bits. 146 * We assume RIGHT_SHIFT rounds towards minus infinity, so adding 147 * the fudge factor is correct for either sign of X. 148 */ 149 150 #define DESCALE(x,n) RIGHT_SHIFT((x) + (ONE << ((n)-1)), n) 151 152 /* Multiply an INT32 variable by an INT32 constant to yield an INT32 result. 153 * This macro is used only when the two inputs will actually be no more than 154 * 16 bits wide, so that a 16x16->32 bit multiply can be used instead of a 155 * full 32x32 multiply. This provides a useful speedup on many machines. 156 * Unfortunately there is no way to specify a 16x16->32 multiply portably 157 * in C, but some C compilers will do the right thing if you provide the 158 * correct combination of casts. 159 */ 160 161 #ifdef SHORTxSHORT_32 /* may work if 'int' is 32 bits */ 162 #define MULTIPLY16C16(var,const) (((INT16) (var)) * ((INT16) (const))) 163 #endif 164 #ifdef SHORTxLCONST_32 /* known to work with Microsoft C 6.0 */ 165 #define MULTIPLY16C16(var,const) (((INT16) (var)) * ((INT32) (const))) 166 #endif 167 168 #ifndef MULTIPLY16C16 /* default definition */ 169 #define MULTIPLY16C16(var,const) ((var) * (const)) 170 #endif 171 172 /* Same except both inputs are variables. */ 173 174 #ifdef SHORTxSHORT_32 /* may work if 'int' is 32 bits */ 175 #define MULTIPLY16V16(var1,var2) (((INT16) (var1)) * ((INT16) (var2))) 176 #endif 177 178 #ifndef MULTIPLY16V16 /* default definition */ 179 #define MULTIPLY16V16(var1,var2) ((var1) * (var2)) 180 #endif 181