source: trunk/libjpeg/jfdctflt.c @ 283

Last change on this file since 283 was 283, checked in by rbri, 12 years ago

JPEG plugin: libjpeg updated to version 7

File size: 6.0 KB
Line 
1/*
2 * jfdctflt.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 floating-point implementation of the
10 * forward DCT (Discrete Cosine Transform).
11 *
12 * This implementation should be more accurate than either of the integer
13 * DCT implementations.  However, it may not give the same results on all
14 * machines because of differences in roundoff behavior.  Speed will depend
15 * on the hardware's floating point capacity.
16 *
17 * A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT
18 * on each column.  Direct algorithms are also available, but they are
19 * much more complex and seem not to be any faster when reduced to code.
20 *
21 * This implementation is based on Arai, Agui, and Nakajima's algorithm for
22 * scaled DCT.  Their original paper (Trans. IEICE E-71(11):1095) is in
23 * Japanese, but the algorithm is described in the Pennebaker & Mitchell
24 * JPEG textbook (see REFERENCES section in file README).  The following code
25 * is based directly on figure 4-8 in P&M.
26 * While an 8-point DCT cannot be done in less than 11 multiplies, it is
27 * possible to arrange the computation so that many of the multiplies are
28 * simple scalings of the final outputs.  These multiplies can then be
29 * folded into the multiplications or divisions by the JPEG quantization
30 * table entries.  The AA&N method leaves only 5 multiplies and 29 adds
31 * to be done in the DCT itself.
32 * The primary disadvantage of this method is that with a fixed-point
33 * implementation, accuracy is lost due to imprecise representation of the
34 * scaled quantization values.  However, that problem does not arise if
35 * we use floating point arithmetic.
36 */
37
38#define JPEG_INTERNALS
39#include "jinclude.h"
40#include "jpeglib.h"
41#include "jdct.h"               /* Private declarations for DCT subsystem */
42
43#ifdef DCT_FLOAT_SUPPORTED
44
45
46/*
47 * This module is specialized to the case DCTSIZE = 8.
48 */
49
50#if DCTSIZE != 8
51  Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
52#endif
53
54
55/*
56 * Perform the forward DCT on one block of samples.
57 */
58
59GLOBAL(void)
60jpeg_fdct_float (FAST_FLOAT * data, JSAMPARRAY sample_data, JDIMENSION start_col)
61{
62  FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
63  FAST_FLOAT tmp10, tmp11, tmp12, tmp13;
64  FAST_FLOAT z1, z2, z3, z4, z5, z11, z13;
65  FAST_FLOAT *dataptr;
66  JSAMPROW elemptr;
67  int ctr;
68
69  /* Pass 1: process rows. */
70
71  dataptr = data;
72  for (ctr = 0; ctr < DCTSIZE; ctr++) {
73    elemptr = sample_data[ctr] + start_col;
74
75    /* Load data into workspace */
76    tmp0 = (FAST_FLOAT) (GETJSAMPLE(elemptr[0]) + GETJSAMPLE(elemptr[7]));
77    tmp7 = (FAST_FLOAT) (GETJSAMPLE(elemptr[0]) - GETJSAMPLE(elemptr[7]));
78    tmp1 = (FAST_FLOAT) (GETJSAMPLE(elemptr[1]) + GETJSAMPLE(elemptr[6]));
79    tmp6 = (FAST_FLOAT) (GETJSAMPLE(elemptr[1]) - GETJSAMPLE(elemptr[6]));
80    tmp2 = (FAST_FLOAT) (GETJSAMPLE(elemptr[2]) + GETJSAMPLE(elemptr[5]));
81    tmp5 = (FAST_FLOAT) (GETJSAMPLE(elemptr[2]) - GETJSAMPLE(elemptr[5]));
82    tmp3 = (FAST_FLOAT) (GETJSAMPLE(elemptr[3]) + GETJSAMPLE(elemptr[4]));
83    tmp4 = (FAST_FLOAT) (GETJSAMPLE(elemptr[3]) - GETJSAMPLE(elemptr[4]));
84
85    /* Even part */
86
87    tmp10 = tmp0 + tmp3;        /* phase 2 */
88    tmp13 = tmp0 - tmp3;
89    tmp11 = tmp1 + tmp2;
90    tmp12 = tmp1 - tmp2;
91
92    /* Apply unsigned->signed conversion */
93    dataptr[0] = tmp10 + tmp11 - 8 * CENTERJSAMPLE; /* phase 3 */
94    dataptr[4] = tmp10 - tmp11;
95
96    z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */
97    dataptr[2] = tmp13 + z1;    /* phase 5 */
98    dataptr[6] = tmp13 - z1;
99
100    /* Odd part */
101
102    tmp10 = tmp4 + tmp5;        /* phase 2 */
103    tmp11 = tmp5 + tmp6;
104    tmp12 = tmp6 + tmp7;
105
106    /* The rotator is modified from fig 4-8 to avoid extra negations. */
107    z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */
108    z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */
109    z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */
110    z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */
111
112    z11 = tmp7 + z3;            /* phase 5 */
113    z13 = tmp7 - z3;
114
115    dataptr[5] = z13 + z2;      /* phase 6 */
116    dataptr[3] = z13 - z2;
117    dataptr[1] = z11 + z4;
118    dataptr[7] = z11 - z4;
119
120    dataptr += DCTSIZE;         /* advance pointer to next row */
121  }
122
123  /* Pass 2: process columns. */
124
125  dataptr = data;
126  for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
127    tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];
128    tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];
129    tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];
130    tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];
131    tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];
132    tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];
133    tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];
134    tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];
135
136    /* Even part */
137
138    tmp10 = tmp0 + tmp3;        /* phase 2 */
139    tmp13 = tmp0 - tmp3;
140    tmp11 = tmp1 + tmp2;
141    tmp12 = tmp1 - tmp2;
142
143    dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */
144    dataptr[DCTSIZE*4] = tmp10 - tmp11;
145
146    z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */
147    dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */
148    dataptr[DCTSIZE*6] = tmp13 - z1;
149
150    /* Odd part */
151
152    tmp10 = tmp4 + tmp5;        /* phase 2 */
153    tmp11 = tmp5 + tmp6;
154    tmp12 = tmp6 + tmp7;
155
156    /* The rotator is modified from fig 4-8 to avoid extra negations. */
157    z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */
158    z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */
159    z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */
160    z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */
161
162    z11 = tmp7 + z3;            /* phase 5 */
163    z13 = tmp7 - z3;
164
165    dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */
166    dataptr[DCTSIZE*3] = z13 - z2;
167    dataptr[DCTSIZE*1] = z11 + z4;
168    dataptr[DCTSIZE*7] = z11 - z4;
169
170    dataptr++;                  /* advance pointer to next column */
171  }
172}
173
174#endif /* DCT_FLOAT_SUPPORTED */
Note: See TracBrowser for help on using the repository browser.