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jdct.h (7041B)
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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