aboutsummaryrefslogtreecommitdiffstats
path: root/code/jpeg-6/jdct.h
blob: 3ce790bc8f62e1f584d32fcff3b6e7098fb3c7b6 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
/*
 * jdct.h
 *
 * Copyright (C) 1994, Thomas G. Lane.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This include file contains common declarations for the forward and
 * inverse DCT modules.  These declarations are private to the DCT managers
 * (jcdctmgr.c, jddctmgr.c) and the individual DCT algorithms.
 * The individual DCT algorithms are kept in separate files to ease 
 * machine-dependent tuning (e.g., assembly coding).
 */


/*
 * A forward DCT routine is given a pointer to a work area of type DCTELEM[];
 * the DCT is to be performed in-place in that buffer.  Type DCTELEM is int
 * for 8-bit samples, INT32 for 12-bit samples.  (NOTE: Floating-point DCT
 * implementations use an array of type FAST_FLOAT, instead.)
 * The DCT inputs are expected to be signed (range +-CENTERJSAMPLE).
 * The DCT outputs are returned scaled up by a factor of 8; they therefore
 * have a range of +-8K for 8-bit data, +-128K for 12-bit data.  This
 * convention improves accuracy in integer implementations and saves some
 * work in floating-point ones.
 * Quantization of the output coefficients is done by jcdctmgr.c.
 */

#if BITS_IN_JSAMPLE == 8
typedef int DCTELEM;		/* 16 or 32 bits is fine */
#else
typedef INT32 DCTELEM;		/* must have 32 bits */
#endif

typedef JMETHOD(void, forward_DCT_method_ptr, (DCTELEM * data));
typedef JMETHOD(void, float_DCT_method_ptr, (FAST_FLOAT * data));


/*
 * An inverse DCT routine is given a pointer to the input JBLOCK and a pointer
 * to an output sample array.  The routine must dequantize the input data as
 * well as perform the IDCT; for dequantization, it uses the multiplier table
 * pointed to by compptr->dct_table.  The output data is to be placed into the
 * sample array starting at a specified column.  (Any row offset needed will
 * be applied to the array pointer before it is passed to the IDCT code.)
 * Note that the number of samples emitted by the IDCT routine is
 * DCT_scaled_size * DCT_scaled_size.
 */

/* typedef inverse_DCT_method_ptr is declared in jpegint.h */

/*
 * Each IDCT routine has its own ideas about the best dct_table element type.
 */

typedef MULTIPLIER ISLOW_MULT_TYPE; /* short or int, whichever is faster */
#if BITS_IN_JSAMPLE == 8
typedef MULTIPLIER IFAST_MULT_TYPE; /* 16 bits is OK, use short if faster */
#define IFAST_SCALE_BITS  2	/* fractional bits in scale factors */
#else
typedef INT32 IFAST_MULT_TYPE;	/* need 32 bits for scaled quantizers */
#define IFAST_SCALE_BITS  13	/* fractional bits in scale factors */
#endif
typedef FAST_FLOAT FLOAT_MULT_TYPE; /* preferred floating type */


/*
 * Each IDCT routine is responsible for range-limiting its results and
 * converting them to unsigned form (0..MAXJSAMPLE).  The raw outputs could
 * be quite far out of range if the input data is corrupt, so a bulletproof
 * range-limiting step is required.  We use a mask-and-table-lookup method
 * to do the combined operations quickly.  See the comments with
 * prepare_range_limit_table (in jdmaster.c) for more info.
 */

#define IDCT_range_limit(cinfo)  ((cinfo)->sample_range_limit + CENTERJSAMPLE)

#define RANGE_MASK  (MAXJSAMPLE * 4 + 3) /* 2 bits wider than legal samples */


/* Short forms of external names for systems with brain-damaged linkers. */

#ifdef NEED_SHORT_EXTERNAL_NAMES
#define jpeg_fdct_islow		jFDislow
#define jpeg_fdct_ifast		jFDifast
#define jpeg_fdct_float		jFDfloat
#define jpeg_idct_islow		jRDislow
#define jpeg_idct_ifast		jRDifast
#define jpeg_idct_float		jRDfloat
#define jpeg_idct_4x4		jRD4x4
#define jpeg_idct_2x2		jRD2x2
#define jpeg_idct_1x1		jRD1x1
#endif /* NEED_SHORT_EXTERNAL_NAMES */

/* Extern declarations for the forward and inverse DCT routines. */

EXTERN void jpeg_fdct_islow JPP((DCTELEM * data));
EXTERN void jpeg_fdct_ifast JPP((DCTELEM * data));
EXTERN void jpeg_fdct_float JPP((FAST_FLOAT * data));

EXTERN void jpeg_idct_islow
    JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
	 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
EXTERN void jpeg_idct_ifast
    JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
	 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
EXTERN void jpeg_idct_float
    JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
	 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
EXTERN void jpeg_idct_4x4
    JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
	 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
EXTERN void jpeg_idct_2x2
    JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
	 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
EXTERN void jpeg_idct_1x1
    JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
	 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));


/*
 * Macros for handling fixed-point arithmetic; these are used by many
 * but not all of the DCT/IDCT modules.
 *
 * All values are expected to be of type INT32.
 * Fractional constants are scaled left by CONST_BITS bits.
 * CONST_BITS is defined within each module using these macros,
 * and may differ from one module to the next.
 */

#define ONE	((INT32) 1)
#define CONST_SCALE (ONE << CONST_BITS)

/* Convert a positive real constant to an integer scaled by CONST_SCALE.
 * Caution: some C compilers fail to reduce "FIX(constant)" at compile time,
 * thus causing a lot of useless floating-point operations at run time.
 */

#define FIX(x)	((INT32) ((x) * CONST_SCALE + 0.5))

/* Descale and correctly round an INT32 value that's scaled by N bits.
 * We assume RIGHT_SHIFT rounds towards minus infinity, so adding
 * the fudge factor is correct for either sign of X.
 */

#define DESCALE(x,n)  RIGHT_SHIFT((x) + (ONE << ((n)-1)), n)

/* Multiply an INT32 variable by an INT32 constant to yield an INT32 result.
 * This macro is used only when the two inputs will actually be no more than
 * 16 bits wide, so that a 16x16->32 bit multiply can be used instead of a
 * full 32x32 multiply.  This provides a useful speedup on many machines.
 * Unfortunately there is no way to specify a 16x16->32 multiply portably
 * in C, but some C compilers will do the right thing if you provide the
 * correct combination of casts.
 */

#ifdef SHORTxSHORT_32		/* may work if 'int' is 32 bits */
#define MULTIPLY16C16(var,const)  (((INT16) (var)) * ((INT16) (const)))
#endif
#ifdef SHORTxLCONST_32		/* known to work with Microsoft C 6.0 */
#define MULTIPLY16C16(var,const)  (((INT16) (var)) * ((INT32) (const)))
#endif

#ifndef MULTIPLY16C16		/* default definition */
#define MULTIPLY16C16(var,const)  ((var) * (const))
#endif

/* Same except both inputs are variables. */

#ifdef SHORTxSHORT_32		/* may work if 'int' is 32 bits */
#define MULTIPLY16V16(var1,var2)  (((INT16) (var1)) * ((INT16) (var2)))
#endif

#ifndef MULTIPLY16V16		/* default definition */
#define MULTIPLY16V16(var1,var2)  ((var1) * (var2))
#endif