/[pcsx2_0.9.7]/trunk/3rdparty/libjpeg/jfdctfst.c
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Revision 10 - (hide annotations) (download)
Mon Sep 6 11:40:06 2010 UTC (10 years ago) by william
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1 william 10 /*
2     * jfdctfst.c
3     *
4     * Copyright (C) 1994-1996, Thomas G. Lane.
5     * Modified 2003-2009 by Guido Vollbeding.
6     * This file is part of the Independent JPEG Group's software.
7     * For conditions of distribution and use, see the accompanying README file.
8     *
9     * This file contains a fast, not so accurate integer implementation of the
10     * forward DCT (Discrete Cosine Transform).
11     *
12     * A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT
13     * on each column. Direct algorithms are also available, but they are
14     * much more complex and seem not to be any faster when reduced to code.
15     *
16     * This implementation is based on Arai, Agui, and Nakajima's algorithm for
17     * scaled DCT. Their original paper (Trans. IEICE E-71(11):1095) is in
18     * Japanese, but the algorithm is described in the Pennebaker & Mitchell
19     * JPEG textbook (see REFERENCES section in file README). The following code
20     * is based directly on figure 4-8 in P&M.
21     * While an 8-point DCT cannot be done in less than 11 multiplies, it is
22     * possible to arrange the computation so that many of the multiplies are
23     * simple scalings of the final outputs. These multiplies can then be
24     * folded into the multiplications or divisions by the JPEG quantization
25     * table entries. The AA&N method leaves only 5 multiplies and 29 adds
26     * to be done in the DCT itself.
27     * The primary disadvantage of this method is that with fixed-point math,
28     * accuracy is lost due to imprecise representation of the scaled
29     * quantization values. The smaller the quantization table entry, the less
30     * precise the scaled value, so this implementation does worse with high-
31     * quality-setting files than with low-quality ones.
32     */
33    
34     #define JPEG_INTERNALS
35     #include "jinclude.h"
36     #include "jpeglib.h"
37     #include "jdct.h" /* Private declarations for DCT subsystem */
38    
39     #ifdef DCT_IFAST_SUPPORTED
40    
41    
42     /*
43     * This module is specialized to the case DCTSIZE = 8.
44     */
45    
46     #if DCTSIZE != 8
47     Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
48     #endif
49    
50    
51     /* Scaling decisions are generally the same as in the LL&M algorithm;
52     * see jfdctint.c for more details. However, we choose to descale
53     * (right shift) multiplication products as soon as they are formed,
54     * rather than carrying additional fractional bits into subsequent additions.
55     * This compromises accuracy slightly, but it lets us save a few shifts.
56     * More importantly, 16-bit arithmetic is then adequate (for 8-bit samples)
57     * everywhere except in the multiplications proper; this saves a good deal
58     * of work on 16-bit-int machines.
59     *
60     * Again to save a few shifts, the intermediate results between pass 1 and
61     * pass 2 are not upscaled, but are represented only to integral precision.
62     *
63     * A final compromise is to represent the multiplicative constants to only
64     * 8 fractional bits, rather than 13. This saves some shifting work on some
65     * machines, and may also reduce the cost of multiplication (since there
66     * are fewer one-bits in the constants).
67     */
68    
69     #define CONST_BITS 8
70    
71    
72     /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
73     * causing a lot of useless floating-point operations at run time.
74     * To get around this we use the following pre-calculated constants.
75     * If you change CONST_BITS you may want to add appropriate values.
76     * (With a reasonable C compiler, you can just rely on the FIX() macro...)
77     */
78    
79     #if CONST_BITS == 8
80     #define FIX_0_382683433 ((INT32) 98) /* FIX(0.382683433) */
81     #define FIX_0_541196100 ((INT32) 139) /* FIX(0.541196100) */
82     #define FIX_0_707106781 ((INT32) 181) /* FIX(0.707106781) */
83     #define FIX_1_306562965 ((INT32) 334) /* FIX(1.306562965) */
84     #else
85     #define FIX_0_382683433 FIX(0.382683433)
86     #define FIX_0_541196100 FIX(0.541196100)
87     #define FIX_0_707106781 FIX(0.707106781)
88     #define FIX_1_306562965 FIX(1.306562965)
89     #endif
90    
91    
92     /* We can gain a little more speed, with a further compromise in accuracy,
93     * by omitting the addition in a descaling shift. This yields an incorrectly
94     * rounded result half the time...
95     */
96    
97     #ifndef USE_ACCURATE_ROUNDING
98     #undef DESCALE
99     #define DESCALE(x,n) RIGHT_SHIFT(x, n)
100     #endif
101    
102    
103     /* Multiply a DCTELEM variable by an INT32 constant, and immediately
104     * descale to yield a DCTELEM result.
105     */
106    
107     #define MULTIPLY(var,const) ((DCTELEM) DESCALE((var) * (const), CONST_BITS))
108    
109    
110     /*
111     * Perform the forward DCT on one block of samples.
112     */
113    
114     GLOBAL(void)
115     jpeg_fdct_ifast (DCTELEM * data, JSAMPARRAY sample_data, JDIMENSION start_col)
116     {
117     DCTELEM tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
118     DCTELEM tmp10, tmp11, tmp12, tmp13;
119     DCTELEM z1, z2, z3, z4, z5, z11, z13;
120     DCTELEM *dataptr;
121     JSAMPROW elemptr;
122     int ctr;
123     SHIFT_TEMPS
124    
125     /* Pass 1: process rows. */
126    
127     dataptr = data;
128     for (ctr = 0; ctr < DCTSIZE; ctr++) {
129     elemptr = sample_data[ctr] + start_col;
130    
131     /* Load data into workspace */
132     tmp0 = GETJSAMPLE(elemptr[0]) + GETJSAMPLE(elemptr[7]);
133     tmp7 = GETJSAMPLE(elemptr[0]) - GETJSAMPLE(elemptr[7]);
134     tmp1 = GETJSAMPLE(elemptr[1]) + GETJSAMPLE(elemptr[6]);
135     tmp6 = GETJSAMPLE(elemptr[1]) - GETJSAMPLE(elemptr[6]);
136     tmp2 = GETJSAMPLE(elemptr[2]) + GETJSAMPLE(elemptr[5]);
137     tmp5 = GETJSAMPLE(elemptr[2]) - GETJSAMPLE(elemptr[5]);
138     tmp3 = GETJSAMPLE(elemptr[3]) + GETJSAMPLE(elemptr[4]);
139     tmp4 = GETJSAMPLE(elemptr[3]) - GETJSAMPLE(elemptr[4]);
140    
141     /* Even part */
142    
143     tmp10 = tmp0 + tmp3; /* phase 2 */
144     tmp13 = tmp0 - tmp3;
145     tmp11 = tmp1 + tmp2;
146     tmp12 = tmp1 - tmp2;
147    
148     /* Apply unsigned->signed conversion */
149     dataptr[0] = tmp10 + tmp11 - 8 * CENTERJSAMPLE; /* phase 3 */
150     dataptr[4] = tmp10 - tmp11;
151    
152     z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */
153     dataptr[2] = tmp13 + z1; /* phase 5 */
154     dataptr[6] = tmp13 - z1;
155    
156     /* Odd part */
157    
158     tmp10 = tmp4 + tmp5; /* phase 2 */
159     tmp11 = tmp5 + tmp6;
160     tmp12 = tmp6 + tmp7;
161    
162     /* The rotator is modified from fig 4-8 to avoid extra negations. */
163     z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */
164     z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */
165     z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */
166     z3 = MULTIPLY(tmp11, FIX_0_707106781); /* c4 */
167    
168     z11 = tmp7 + z3; /* phase 5 */
169     z13 = tmp7 - z3;
170    
171     dataptr[5] = z13 + z2; /* phase 6 */
172     dataptr[3] = z13 - z2;
173     dataptr[1] = z11 + z4;
174     dataptr[7] = z11 - z4;
175    
176     dataptr += DCTSIZE; /* advance pointer to next row */
177     }
178    
179     /* Pass 2: process columns. */
180    
181     dataptr = data;
182     for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
183     tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];
184     tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];
185     tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];
186     tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];
187     tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];
188     tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];
189     tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];
190     tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];
191    
192     /* Even part */
193    
194     tmp10 = tmp0 + tmp3; /* phase 2 */
195     tmp13 = tmp0 - tmp3;
196     tmp11 = tmp1 + tmp2;
197     tmp12 = tmp1 - tmp2;
198    
199     dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */
200     dataptr[DCTSIZE*4] = tmp10 - tmp11;
201    
202     z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */
203     dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */
204     dataptr[DCTSIZE*6] = tmp13 - z1;
205    
206     /* Odd part */
207    
208     tmp10 = tmp4 + tmp5; /* phase 2 */
209     tmp11 = tmp5 + tmp6;
210     tmp12 = tmp6 + tmp7;
211    
212     /* The rotator is modified from fig 4-8 to avoid extra negations. */
213     z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */
214     z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */
215     z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */
216     z3 = MULTIPLY(tmp11, FIX_0_707106781); /* c4 */
217    
218     z11 = tmp7 + z3; /* phase 5 */
219     z13 = tmp7 - z3;
220    
221     dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */
222     dataptr[DCTSIZE*3] = z13 - z2;
223     dataptr[DCTSIZE*1] = z11 + z4;
224     dataptr[DCTSIZE*7] = z11 - z4;
225    
226     dataptr++; /* advance pointer to next column */
227     }
228     }
229    
230     #endif /* DCT_IFAST_SUPPORTED */

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