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
|
/*****************************************************************************
* idct.h : macros for the inverse discrete cosine transform
*****************************************************************************
* Copyright (C) 1999, 2000 VideoLAN
* $Id: idct.h,v 1.5 2001/09/05 16:07:49 massiot Exp $
*
* Authors: Gal Hendryckx <jimmy@via.ecp.fr>
* Christophe Massiot <massiot@via.ecp.fr>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111, USA.
*****************************************************************************/
#define SPARSE_SCALE_FACTOR 8
#define DCTSIZE 8 /* 8*8 DCT */
/*****************************************************************************
* Macros
*****************************************************************************/
/* We assume that right shift corresponds to signed division by 2 with
* rounding towards minus infinity. This is correct for typical "arithmetic
* shift" instructions that shift in copies of the sign bit. But some
* C compilers implement >> with an unsigned shift. For these machines you
* must define RIGHT_SHIFT_IS_UNSIGNED.
* RIGHT_SHIFT provides a proper signed right shift of an s32 quantity.
* It is only applied with constant shift counts. SHIFT_TEMPS must be
* included in the variables of any routine using RIGHT_SHIFT.
*/
#ifdef RIGHT_SHIFT_IS_UNSIGNED
#define SHIFT_TEMPS s32 shift_temp;
#define RIGHT_SHIFT(x,shft) \
((shift_temp = (x)) < 0 ? \
(shift_temp >> (shft)) | ((~((s32) 0)) << (32-(shft))) : \
(shift_temp >> (shft)))
#else
#define SHIFT_TEMPS
#define RIGHT_SHIFT(x,shft) ((x) >> (shft))
#endif
/*
* A 2-D IDCT can be done by 1-D IDCT on each row followed by 1-D IDCT
* on each column. Direct algorithms are also available, but they are
* much more complex and seem not to be any faster when reduced to code.
*
* The poop on this scaling stuff is as follows:
*
* Each 1-D IDCT step produces outputs which are a factor of sqrt(N)
* larger than the true IDCT outputs. The final outputs are therefore
* a factor of N larger than desired; since N=8 this can be cured by
* a simple right shift at the end of the algorithm. The advantage of
* this arrangement is that we save two multiplications per 1-D IDCT,
* because the y0 and y4 inputs need not be divided by sqrt(N).
*
* We have to do addition and subtraction of the integer inputs, which
* is no problem, and multiplication by fractional constants, which is
* a problem to do in integer arithmetic. We multiply all the constants
* by CONST_SCALE and convert them to integer constants (thus retaining
* CONST_BITS bits of precision in the constants). After doing a
* multiplication we have to divide the product by CONST_SCALE, with proper
* rounding, to produce the correct output. This division can be done
* cheaply as a right shift of CONST_BITS bits. We postpone shifting
* as long as possible so that partial sums can be added together with
* full fractional precision.
*
* The outputs of the first pass are scaled up by PASS1_BITS bits so that
* they are represented to better-than-integral precision. These outputs
* require BITS_IN_JSAMPLE + PASS1_BITS + 3 bits; this fits in a 16-bit word
* with the recommended scaling. (To scale up 12-bit sample data further, an
* intermediate s32 array would be needed.)
*
* To avoid overflow of the 32-bit intermediate results in pass 2, we must
* have BITS_IN_JSAMPLE + CONST_BITS + PASS1_BITS <= 26. Error analysis
* shows that the values given below are the most effective.
*/
#define CONST_BITS 8 /* Jimmy chose this constant :) */
#ifdef EIGHT_BIT_SAMPLES
#define PASS1_BITS 2
#else
#define PASS1_BITS 1 /* lose a little precision to avoid overflow */
#endif
#define ONE ((s32) 1)
#define CONST_SCALE (ONE << CONST_BITS)
/* Convert a positive real constant to an integer scaled by CONST_SCALE.
* IMPORTANT: if your compiler doesn't do this arithmetic at compile time,
* you will pay a significant penalty in run time. In that case, figure
* the correct integer constant values and insert them by hand.
*/
#define FIX(x) ((s32) ((x) * CONST_SCALE + 0.5))
/* When adding two opposite-signed fixes, the 0.5 cancels */
#define FIX2(x) ((s32) ((x) * CONST_SCALE))
/* Descale and correctly round an s32 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 s32 variable by an s32 constant to yield an s32 result.
* For 8-bit samples with the recommended scaling, all the variable
* and constant values involved are no more than 16 bits wide, so a
* 16x16->32 bit multiply can be used instead of a full 32x32 multiply;
* this provides a useful speedup on many machines.
* There is no way to specify a 16x16->32 multiply in portable C, but
* some C compilers will do the right thing if you provide the correct
* combination of casts.
* NB: for 12-bit samples, a full 32-bit multiplication will be needed.
*/
#ifdef EIGHT_BIT_SAMPLES
#ifdef SHORTxSHORT_32 /* may work if 'int' is 32 bits */
#define MULTIPLY(var,const) (((INT16) (var)) * ((INT16) (const)))
#endif
#ifdef SHORTxLCONST_32 /* known to work with Microsoft C 6.0 */
#define MULTIPLY(var,const) (((INT16) (var)) * ((s32) (const)))
#endif
#endif
#ifndef MULTIPLY /* default definition */
#define MULTIPLY(var,const) ((var) * (const))
#endif
|
