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 /* Extern declarations for the forward and inverse DCT routines. */ 84 85 EXTERN(void) jpeg_fdct_islow JPP((DCTELEM * data)); 86 EXTERN(void) jpeg_fdct_ifast JPP((DCTELEM * data)); 87 EXTERN(void) jpeg_fdct_float JPP((FAST_FLOAT * data)); 88 89 EXTERN(void) jpeg_idct_islow 90 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, 91 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); 92 EXTERN(void) jpeg_idct_ifast 93 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, 94 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); 95 EXTERN(void) jpeg_idct_float 96 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, 97 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); 98 EXTERN(void) jpeg_idct_4x4 99 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, 100 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); 101 EXTERN(void) jpeg_idct_2x2 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_1x1 105 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, 106 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); 107 108 109 /* 110 * Macros for handling fixed-point arithmetic; these are used by many 111 * but not all of the DCT/IDCT modules. 112 * 113 * All values are expected to be of type INT32. 114 * Fractional constants are scaled left by CONST_BITS bits. 115 * CONST_BITS is defined within each module using these macros, 116 * and may differ from one module to the next. 117 */ 118 119 #define ONE ((INT32) 1) 120 #define CONST_SCALE (ONE << CONST_BITS) 121 122 /* Convert a positive real constant to an integer scaled by CONST_SCALE. 123 * Caution: some C compilers fail to reduce "FIX(constant)" at compile time, 124 * thus causing a lot of useless floating-point operations at run time. 125 */ 126 127 #define FIX(x) ((INT32) ((x) * CONST_SCALE + 0.5)) 128 129 /* Descale and correctly round an INT32 value that's scaled by N bits. 130 * We assume RIGHT_SHIFT rounds towards minus infinity, so adding 131 * the fudge factor is correct for either sign of X. 132 */ 133 134 #define DESCALE(x,n) RIGHT_SHIFT((x) + (ONE << ((n)-1)), n) 135 136 /* Multiply an INT32 variable by an INT32 constant to yield an INT32 result. 137 * This macro is used only when the two inputs will actually be no more than 138 * 16 bits wide, so that a 16x16->32 bit multiply can be used instead of a 139 * full 32x32 multiply. This provides a useful speedup on many machines. 140 * Unfortunately there is no way to specify a 16x16->32 multiply portably 141 * in C, but some C compilers will do the right thing if you provide the 142 * correct combination of casts. 143 */ 144 145 #ifdef SHORTxSHORT_32 /* may work if 'int' is 32 bits */ 146 #define MULTIPLY16C16(var,const) (((INT16) (var)) * ((INT16) (const))) 147 #endif 148 #ifdef SHORTxLCONST_32 /* known to work with Microsoft C 6.0 */ 149 #define MULTIPLY16C16(var,const) (((INT16) (var)) * ((INT32) (const))) 150 #endif 151 152 #ifndef MULTIPLY16C16 /* default definition */ 153 #define MULTIPLY16C16(var,const) ((var) * (const)) 154 #endif 155 156 /* Same except both inputs are variables. */ 157 158 #ifdef SHORTxSHORT_32 /* may work if 'int' is 32 bits */ 159 #define MULTIPLY16V16(var1,var2) (((INT16) (var1)) * ((INT16) (var2))) 160 #endif 161 162 #ifndef MULTIPLY16V16 /* default definition */ 163 #define MULTIPLY16V16(var1,var2) ((var1) * (var2)) 164 #endif 165