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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 | #ifdef NEED_SHORT_EXTERNAL_NAMES | |
84 | #define jpeg_fdct_islow jFDislow | |
85 | #define jpeg_fdct_ifast jFDifast | |
86 | #define jpeg_fdct_float jFDfloat | |
87 | #define jpeg_idct_islow jRDislow | |
88 | #define jpeg_idct_ifast jRDifast | |
89 | #define jpeg_idct_float jRDfloat | |
90 | #define jpeg_idct_4x4 jRD4x4 | |
91 | #define jpeg_idct_2x2 jRD2x2 | |
92 | #define jpeg_idct_1x1 jRD1x1 | |
93 | #endif /* NEED_SHORT_EXTERNAL_NAMES */ | |
94 | ||
95 | /* Extern declarations for the forward and inverse DCT routines. */ | |
96 | ||
97 | EXTERN(void) jpeg_fdct_islow JPP((DCTELEM * data)); | |
98 | EXTERN(void) jpeg_fdct_ifast JPP((DCTELEM * data)); | |
99 | EXTERN(void) jpeg_fdct_float JPP((FAST_FLOAT * data)); | |
100 | ||
101 | EXTERN(void) jpeg_idct_islow | |
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_ifast | |
105 | JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, | |
106 | JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); | |
107 | EXTERN(void) jpeg_idct_float | |
108 | JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, | |
109 | JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); | |
110 | EXTERN(void) jpeg_idct_4x4 | |
111 | JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, | |
112 | JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); | |
113 | EXTERN(void) jpeg_idct_2x2 | |
114 | JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, | |
115 | JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); | |
116 | EXTERN(void) jpeg_idct_1x1 | |
117 | JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, | |
118 | JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); | |
119 | ||
120 | ||
121 | /* | |
122 | * Macros for handling fixed-point arithmetic; these are used by many | |
123 | * but not all of the DCT/IDCT modules. | |
124 | * | |
125 | * All values are expected to be of type INT32. | |
126 | * Fractional constants are scaled left by CONST_BITS bits. | |
127 | * CONST_BITS is defined within each module using these macros, | |
128 | * and may differ from one module to the next. | |
129 | */ | |
130 | ||
131 | #define ONE ((INT32) 1) | |
132 | #define CONST_SCALE (ONE << CONST_BITS) | |
133 | ||
134 | /* Convert a positive real constant to an integer scaled by CONST_SCALE. | |
135 | * Caution: some C compilers fail to reduce "FIX(constant)" at compile time, | |
136 | * thus causing a lot of useless floating-point operations at run time. | |
137 | */ | |
138 | ||
139 | #define FIX(x) ((INT32) ((x) * CONST_SCALE + 0.5)) | |
140 | ||
141 | /* Descale and correctly round an INT32 value that's scaled by N bits. | |
142 | * We assume RIGHT_SHIFT rounds towards minus infinity, so adding | |
143 | * the fudge factor is correct for either sign of X. | |
144 | */ | |
145 | ||
146 | #define DESCALE(x,n) RIGHT_SHIFT((x) + (ONE << ((n)-1)), n) | |
147 | ||
148 | /* Multiply an INT32 variable by an INT32 constant to yield an INT32 result. | |
149 | * This macro is used only when the two inputs will actually be no more than | |
150 | * 16 bits wide, so that a 16x16->32 bit multiply can be used instead of a | |
151 | * full 32x32 multiply. This provides a useful speedup on many machines. | |
152 | * Unfortunately there is no way to specify a 16x16->32 multiply portably | |
153 | * in C, but some C compilers will do the right thing if you provide the | |
154 | * correct combination of casts. | |
155 | */ | |
156 | ||
157 | #ifdef SHORTxSHORT_32 /* may work if 'int' is 32 bits */ | |
158 | #define MULTIPLY16C16(var,const) (((INT16) (var)) * ((INT16) (const))) | |
159 | #endif | |
160 | #ifdef SHORTxLCONST_32 /* known to work with Microsoft C 6.0 */ | |
161 | #define MULTIPLY16C16(var,const) (((INT16) (var)) * ((INT32) (const))) | |
162 | #endif | |
163 | ||
164 | #ifndef MULTIPLY16C16 /* default definition */ | |
165 | #define MULTIPLY16C16(var,const) ((var) * (const)) | |
166 | #endif | |
167 | ||
168 | /* Same except both inputs are variables. */ | |
169 | ||
170 | #ifdef SHORTxSHORT_32 /* may work if 'int' is 32 bits */ | |
171 | #define MULTIPLY16V16(var1,var2) (((INT16) (var1)) * ((INT16) (var2))) | |
172 | #endif | |
173 | ||
174 | #ifndef MULTIPLY16V16 /* default definition */ | |
175 | #define MULTIPLY16V16(var1,var2) ((var1) * (var2)) | |
176 | #endif |