source: golgotha/src/i4/loaders/jpg/jfdctfst.cc @ 80

Last change on this file since 80 was 80, checked in by Sam Hocevar, 11 years ago
  • Adding the Golgotha source code. Not sure what's going to be interesting in there, but since it's all public domain, there's certainly stuff to pick up.
File size: 8.1 KB
Line 
1/********************************************************************** <BR>
2  This file is part of Crack dot Com's free source code release of
3  Golgotha. <a href="http://www.crack.com/golgotha_release"> <BR> for
4  information about compiling & licensing issues visit this URL</a>
5  <PRE> If that doesn't help, contact Jonathan Clark at
6  golgotha_source@usa.net (Subject should have "GOLG" in it)
7***********************************************************************/
8
9/*
10 * jfdctfst.c
11 *
12 * Copyright (C) 1994-1996, Thomas G. Lane.
13 * This file is part of the Independent JPEG Group's software.
14 * For conditions of distribution and use, see the accompanying README file.
15 *
16 * This file contains a fast, not so accurate integer implementation of the
17 * forward DCT (Discrete Cosine Transform).
18 *
19 * A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT
20 * on each column.  Direct algorithms are also available, but they are
21 * much more complex and seem not to be any faster when reduced to code.
22 *
23 * This implementation is based on Arai, Agui, and Nakajima's algorithm for
24 * scaled DCT.  Their original paper (Trans. IEICE E-71(11):1095) is in
25 * Japanese, but the algorithm is described in the Pennebaker & Mitchell
26 * JPEG textbook (see REFERENCES section in file README).  The following code
27 * is based directly on figure 4-8 in P&M.
28 * While an 8-point DCT cannot be done in less than 11 multiplies, it is
29 * possible to arrange the computation so that many of the multiplies are
30 * simple scalings of the final outputs.  These multiplies can then be
31 * folded into the multiplications or divisions by the JPEG quantization
32 * table entries.  The AA&N method leaves only 5 multiplies and 29 adds
33 * to be done in the DCT itself.
34 * The primary disadvantage of this method is that with fixed-point math,
35 * accuracy is lost due to imprecise representation of the scaled
36 * quantization values.  The smaller the quantization table entry, the less
37 * precise the scaled value, so this implementation does worse with high-
38 * quality-setting files than with low-quality ones.
39 */
40
41#define JPEG_INTERNALS
42#include "loaders/jpg/jinclude.h"
43#include "loaders/jpg/jpeglib.h"
44#include "loaders/jpg/jdct.h"           /* Private declarations for DCT subsystem */
45
46#ifdef DCT_IFAST_SUPPORTED
47
48
49/*
50 * This module is specialized to the case DCTSIZE = 8.
51 */
52
53#if DCTSIZE != 8
54  Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
55#endif
56
57
58/* Scaling decisions are generally the same as in the LL&M algorithm;
59 * see jfdctint.c for more details.  However, we choose to descale
60 * (right shift) multiplication products as soon as they are formed,
61 * rather than carrying additional fractional bits into subsequent additions.
62 * This compromises accuracy slightly, but it lets us save a few shifts.
63 * More importantly, 16-bit arithmetic is then adequate (for 8-bit samples)
64 * everywhere except in the multiplications proper; this saves a good deal
65 * of work on 16-bit-int machines.
66 *
67 * Again to save a few shifts, the intermediate results between pass 1 and
68 * pass 2 are not upscaled, but are represented only to integral precision.
69 *
70 * A final compromise is to represent the multiplicative constants to only
71 * 8 fractional bits, rather than 13.  This saves some shifting work on some
72 * machines, and may also reduce the cost of multiplication (since there
73 * are fewer one-bits in the constants).
74 */
75
76#define CONST_BITS  8
77
78
79/* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
80 * causing a lot of useless floating-point operations at run time.
81 * To get around this we use the following pre-calculated constants.
82 * If you change CONST_BITS you may want to add appropriate values.
83 * (With a reasonable C compiler, you can just rely on the FIX() macro...)
84 */
85
86#if CONST_BITS == 8
87#define FIX_0_382683433  ((INT32)   98)         /* FIX(0.382683433) */
88#define FIX_0_541196100  ((INT32)  139)         /* FIX(0.541196100) */
89#define FIX_0_707106781  ((INT32)  181)         /* FIX(0.707106781) */
90#define FIX_1_306562965  ((INT32)  334)         /* FIX(1.306562965) */
91#else
92#define FIX_0_382683433  FIX(0.382683433)
93#define FIX_0_541196100  FIX(0.541196100)
94#define FIX_0_707106781  FIX(0.707106781)
95#define FIX_1_306562965  FIX(1.306562965)
96#endif
97
98
99/* We can gain a little more speed, with a further compromise in accuracy,
100 * by omitting the addition in a descaling shift.  This yields an incorrectly
101 * rounded result half the time...
102 */
103
104#ifndef USE_ACCURATE_ROUNDING
105#undef DESCALE
106#define DESCALE(x,n)  RIGHT_SHIFT(x, n)
107#endif
108
109
110/* Multiply a DCTELEM variable by an INT32 constant, and immediately
111 * descale to yield a DCTELEM result.
112 */
113
114#define MULTIPLY(var,const)  ((DCTELEM) DESCALE((var) * (const), CONST_BITS))
115
116
117/*
118 * Perform the forward DCT on one block of samples.
119 */
120
121GLOBAL(void)
122jpeg_fdct_ifast (DCTELEM * data)
123{
124  DCTELEM tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
125  DCTELEM tmp10, tmp11, tmp12, tmp13;
126  DCTELEM z1, z2, z3, z4, z5, z11, z13;
127  DCTELEM *dataptr;
128  int ctr;
129  SHIFT_TEMPS
130
131  /* Pass 1: process rows. */
132
133  dataptr = data;
134  for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
135    tmp0 = dataptr[0] + dataptr[7];
136    tmp7 = dataptr[0] - dataptr[7];
137    tmp1 = dataptr[1] + dataptr[6];
138    tmp6 = dataptr[1] - dataptr[6];
139    tmp2 = dataptr[2] + dataptr[5];
140    tmp5 = dataptr[2] - dataptr[5];
141    tmp3 = dataptr[3] + dataptr[4];
142    tmp4 = dataptr[3] - dataptr[4];
143   
144    /* Even part */
145   
146    tmp10 = tmp0 + tmp3;        /* phase 2 */
147    tmp13 = tmp0 - tmp3;
148    tmp11 = tmp1 + tmp2;
149    tmp12 = tmp1 - tmp2;
150   
151    dataptr[0] = tmp10 + tmp11; /* phase 3 */
152    dataptr[4] = tmp10 - tmp11;
153   
154    z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */
155    dataptr[2] = tmp13 + z1;    /* phase 5 */
156    dataptr[6] = tmp13 - z1;
157   
158    /* Odd part */
159
160    tmp10 = tmp4 + tmp5;        /* phase 2 */
161    tmp11 = tmp5 + tmp6;
162    tmp12 = tmp6 + tmp7;
163
164    /* The rotator is modified from fig 4-8 to avoid extra negations. */
165    z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */
166    z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */
167    z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */
168    z3 = MULTIPLY(tmp11, FIX_0_707106781); /* c4 */
169
170    z11 = tmp7 + z3;            /* phase 5 */
171    z13 = tmp7 - z3;
172
173    dataptr[5] = z13 + z2;      /* phase 6 */
174    dataptr[3] = z13 - z2;
175    dataptr[1] = z11 + z4;
176    dataptr[7] = z11 - z4;
177
178    dataptr += DCTSIZE;         /* advance pointer to next row */
179  }
180
181  /* Pass 2: process columns. */
182
183  dataptr = data;
184  for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
185    tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];
186    tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];
187    tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];
188    tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];
189    tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];
190    tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];
191    tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];
192    tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];
193   
194    /* Even part */
195   
196    tmp10 = tmp0 + tmp3;        /* phase 2 */
197    tmp13 = tmp0 - tmp3;
198    tmp11 = tmp1 + tmp2;
199    tmp12 = tmp1 - tmp2;
200   
201    dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */
202    dataptr[DCTSIZE*4] = tmp10 - tmp11;
203   
204    z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */
205    dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */
206    dataptr[DCTSIZE*6] = tmp13 - z1;
207   
208    /* Odd part */
209
210    tmp10 = tmp4 + tmp5;        /* phase 2 */
211    tmp11 = tmp5 + tmp6;
212    tmp12 = tmp6 + tmp7;
213
214    /* The rotator is modified from fig 4-8 to avoid extra negations. */
215    z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */
216    z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */
217    z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */
218    z3 = MULTIPLY(tmp11, FIX_0_707106781); /* c4 */
219
220    z11 = tmp7 + z3;            /* phase 5 */
221    z13 = tmp7 - z3;
222
223    dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */
224    dataptr[DCTSIZE*3] = z13 - z2;
225    dataptr[DCTSIZE*1] = z11 + z4;
226    dataptr[DCTSIZE*7] = z11 - z4;
227
228    dataptr++;                  /* advance pointer to next column */
229  }
230}
231
232#endif /* DCT_IFAST_SUPPORTED */
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