00001 /* 00002 * jdct.h 00003 * 00004 * Copyright (C) 1994-1996, Thomas G. Lane. 00005 * This file is part of the Independent JPEG Group's software. 00006 * For conditions of distribution and use, see the accompanying README file. 00007 * 00008 * This include file contains common declarations for the forward and 00009 * inverse DCT modules. These declarations are private to the DCT managers 00010 * (jcdctmgr.c, jddctmgr.c) and the individual DCT algorithms. 00011 * The individual DCT algorithms are kept in separate files to ease 00012 * machine-dependent tuning (e.g., assembly coding). 00013 */ 00014 00015 00016 /* 00017 * A forward DCT routine is given a pointer to a work area of type DCTELEM[]; 00018 * the DCT is to be performed in-place in that buffer. Type DCTELEM is int 00019 * for 8-bit samples, INT32 for 12-bit samples. (NOTE: Floating-point DCT 00020 * implementations use an array of type FAST_FLOAT, instead.) 00021 * The DCT inputs are expected to be signed (range +-CENTERJSAMPLE). 00022 * The DCT outputs are returned scaled up by a factor of 8; they therefore 00023 * have a range of +-8K for 8-bit data, +-128K for 12-bit data. This 00024 * convention improves accuracy in integer implementations and saves some 00025 * work in floating-point ones. 00026 * Quantization of the output coefficients is done by jcdctmgr.c. 00027 */ 00028 00029 #if BITS_IN_JSAMPLE == 8 00030 typedef int DCTELEM; /* 16 or 32 bits is fine */ 00031 #else 00032 typedef INT32 DCTELEM; /* must have 32 bits */ 00033 #endif 00034 00035 typedef JMETHOD(void, forward_DCT_method_ptr, (DCTELEM * data)); 00036 typedef JMETHOD(void, float_DCT_method_ptr, (FAST_FLOAT * data)); 00037 00038 00039 /* 00040 * An inverse DCT routine is given a pointer to the input JBLOCK and a pointer 00041 * to an output sample array. The routine must dequantize the input data as 00042 * well as perform the IDCT; for dequantization, it uses the multiplier table 00043 * pointed to by compptr->dct_table. The output data is to be placed into the 00044 * sample array starting at a specified column. (Any row offset needed will 00045 * be applied to the array pointer before it is passed to the IDCT code.) 00046 * Note that the number of samples emitted by the IDCT routine is 00047 * DCT_scaled_size * DCT_scaled_size. 00048 */ 00049 00050 /* typedef inverse_DCT_method_ptr is declared in jpegint.h */ 00051 00052 /* 00053 * Each IDCT routine has its own ideas about the best dct_table element type. 00054 */ 00055 00056 typedef MULTIPLIER ISLOW_MULT_TYPE; /* short or int, whichever is faster */ 00057 #if BITS_IN_JSAMPLE == 8 00058 typedef MULTIPLIER IFAST_MULT_TYPE; /* 16 bits is OK, use short if faster */ 00059 #define IFAST_SCALE_BITS 2 /* fractional bits in scale factors */ 00060 #else 00061 typedef INT32 IFAST_MULT_TYPE; /* need 32 bits for scaled quantizers */ 00062 #define IFAST_SCALE_BITS 13 /* fractional bits in scale factors */ 00063 #endif 00064 typedef FAST_FLOAT FLOAT_MULT_TYPE; /* preferred floating type */ 00065 00066 00067 /* 00068 * Each IDCT routine is responsible for range-limiting its results and 00069 * converting them to unsigned form (0..MAXJSAMPLE). The raw outputs could 00070 * be quite far out of range if the input data is corrupt, so a bulletproof 00071 * range-limiting step is required. We use a mask-and-table-lookup method 00072 * to do the combined operations quickly. See the comments with 00073 * prepare_range_limit_table (in jdmaster.c) for more info. 00074 */ 00075 00076 #define IDCT_range_limit(cinfo) ((cinfo)->sample_range_limit + CENTERJSAMPLE) 00077 00078 #define RANGE_MASK (MAXJSAMPLE * 4 + 3) /* 2 bits wider than legal samples */ 00079 00080 00081 /* Short forms of external names for systems with brain-damaged linkers. */ 00082 00083 #ifdef NEED_SHORT_EXTERNAL_NAMES 00084 #define jpeg_fdct_islow jFDislow 00085 #define jpeg_fdct_ifast jFDifast 00086 #define jpeg_fdct_float jFDfloat 00087 #define jpeg_idct_islow jRDislow 00088 #define jpeg_idct_ifast jRDifast 00089 #define jpeg_idct_float jRDfloat 00090 #define jpeg_idct_4x4 jRD4x4 00091 #define jpeg_idct_2x2 jRD2x2 00092 #define jpeg_idct_1x1 jRD1x1 00093 #endif /* NEED_SHORT_EXTERNAL_NAMES */ 00094 00095 /* Extern declarations for the forward and inverse DCT routines. */ 00096 00097 EXTERN(void) jpeg_fdct_islow JPP((DCTELEM * data)); 00098 EXTERN(void) jpeg_fdct_ifast JPP((DCTELEM * data)); 00099 EXTERN(void) jpeg_fdct_float JPP((FAST_FLOAT * data)); 00100 00101 EXTERN(void) jpeg_idct_islow 00102 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, 00103 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); 00104 EXTERN(void) jpeg_idct_ifast 00105 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, 00106 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); 00107 EXTERN(void) jpeg_idct_float 00108 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, 00109 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); 00110 EXTERN(void) jpeg_idct_4x4 00111 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, 00112 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); 00113 EXTERN(void) jpeg_idct_2x2 00114 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, 00115 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); 00116 EXTERN(void) jpeg_idct_1x1 00117 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, 00118 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); 00119 00120 00121 /* 00122 * Macros for handling fixed-point arithmetic; these are used by many 00123 * but not all of the DCT/IDCT modules. 00124 * 00125 * All values are expected to be of type INT32. 00126 * Fractional constants are scaled left by CONST_BITS bits. 00127 * CONST_BITS is defined within each module using these macros, 00128 * and may differ from one module to the next. 00129 */ 00130 00131 #define ONE ((INT32) 1) 00132 #define CONST_SCALE (ONE << CONST_BITS) 00133 00134 /* Convert a positive real constant to an integer scaled by CONST_SCALE. 00135 * Caution: some C compilers fail to reduce "FIX(constant)" at compile time, 00136 * thus causing a lot of useless floating-point operations at run time. 00137 */ 00138 00139 #define FIX(x) ((INT32) ((x) * CONST_SCALE + 0.5)) 00140 00141 /* Descale and correctly round an INT32 value that's scaled by N bits. 00142 * We assume RIGHT_SHIFT rounds towards minus infinity, so adding 00143 * the fudge factor is correct for either sign of X. 00144 */ 00145 00146 #define DESCALE(x,n) RIGHT_SHIFT((x) + (ONE << ((n)-1)), n) 00147 00148 /* Multiply an INT32 variable by an INT32 constant to yield an INT32 result. 00149 * This macro is used only when the two inputs will actually be no more than 00150 * 16 bits wide, so that a 16x16->32 bit multiply can be used instead of a 00151 * full 32x32 multiply. This provides a useful speedup on many machines. 00152 * Unfortunately there is no way to specify a 16x16->32 multiply portably 00153 * in C, but some C compilers will do the right thing if you provide the 00154 * correct combination of casts. 00155 */ 00156 00157 #ifdef SHORTxSHORT_32 /* may work if 'int' is 32 bits */ 00158 #define MULTIPLY16C16(var,const) (((INT16) (var)) * ((INT16) (const))) 00159 #endif 00160 #ifdef SHORTxLCONST_32 /* known to work with Microsoft C 6.0 */ 00161 #define MULTIPLY16C16(var,const) (((INT16) (var)) * ((INT32) (const))) 00162 #endif 00163 00164 #ifndef MULTIPLY16C16 /* default definition */ 00165 #define MULTIPLY16C16(var,const) ((var) * (const)) 00166 #endif 00167 00168 /* Same except both inputs are variables. */ 00169 00170 #ifdef SHORTxSHORT_32 /* may work if 'int' is 32 bits */ 00171 #define MULTIPLY16V16(var1,var2) (((INT16) (var1)) * ((INT16) (var2))) 00172 #endif 00173 00174 #ifndef MULTIPLY16V16 /* default definition */ 00175 #define MULTIPLY16V16(var1,var2) ((var1) * (var2)) 00176 #endif