1/*
2 * reserved comment block
3 * DO NOT REMOVE OR ALTER!
4 */
5/*
6 * jfdctflt.c
7 *
8 * Copyright (C) 1994-1996, Thomas G. Lane.
9 * This file is part of the Independent JPEG Group's software.
10 * For conditions of distribution and use, see the accompanying README file.
11 *
12 * This file contains a floating-point implementation of the
13 * forward DCT (Discrete Cosine Transform).
14 *
15 * This implementation should be more accurate than either of the integer
16 * DCT implementations. However, it may not give the same results on all
17 * machines because of differences in roundoff behavior. Speed will depend
18 * on the hardware's floating point capacity.
19 *
20 * A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT
21 * on each column. Direct algorithms are also available, but they are
22 * much more complex and seem not to be any faster when reduced to code.
23 *
24 * This implementation is based on Arai, Agui, and Nakajima's algorithm for
25 * scaled DCT. Their original paper (Trans. IEICE E-71(11):1095) is in
26 * Japanese, but the algorithm is described in the Pennebaker & Mitchell
27 * JPEG textbook (see REFERENCES section in file README). The following code
28 * is based directly on figure 4-8 in P&M.
29 * While an 8-point DCT cannot be done in less than 11 multiplies, it is
30 * possible to arrange the computation so that many of the multiplies are
31 * simple scalings of the final outputs. These multiplies can then be
32 * folded into the multiplications or divisions by the JPEG quantization
33 * table entries. The AA&N method leaves only 5 multiplies and 29 adds
34 * to be done in the DCT itself.
35 * The primary disadvantage of this method is that with a fixed-point
36 * implementation, accuracy is lost due to imprecise representation of the
37 * scaled quantization values. However, that problem does not arise if
38 * we use floating point arithmetic.
39 */
40
41#define JPEG_INTERNALS
42#include "jinclude.h"
43#include "jpeglib.h"
44#include "jdct.h" /* Private declarations for DCT subsystem */
45
46#ifdef DCT_FLOAT_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/*
59 * Perform the forward DCT on one block of samples.
60 */
61
62GLOBAL(void)
63jpeg_fdct_float (FAST_FLOAT * data)
64{
65 FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
66 FAST_FLOAT tmp10, tmp11, tmp12, tmp13;
67 FAST_FLOAT z1, z2, z3, z4, z5, z11, z13;
68 FAST_FLOAT *dataptr;
69 int ctr;
70
71 /* Pass 1: process rows. */
72
73 dataptr = data;
74 for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
75 tmp0 = dataptr[0] + dataptr[7];
76 tmp7 = dataptr[0] - dataptr[7];
77 tmp1 = dataptr[1] + dataptr[6];
78 tmp6 = dataptr[1] - dataptr[6];
79 tmp2 = dataptr[2] + dataptr[5];
80 tmp5 = dataptr[2] - dataptr[5];
81 tmp3 = dataptr[3] + dataptr[4];
82 tmp4 = dataptr[3] - dataptr[4];
83
84 /* Even part */
85
86 tmp10 = tmp0 + tmp3; /* phase 2 */
87 tmp13 = tmp0 - tmp3;
88 tmp11 = tmp1 + tmp2;
89 tmp12 = tmp1 - tmp2;
90
91 dataptr[0] = tmp10 + tmp11; /* phase 3 */
92 dataptr[4] = tmp10 - tmp11;
93
94 z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */
95 dataptr[2] = tmp13 + z1; /* phase 5 */
96 dataptr[6] = tmp13 - z1;
97
98 /* Odd part */
99
100 tmp10 = tmp4 + tmp5; /* phase 2 */
101 tmp11 = tmp5 + tmp6;
102 tmp12 = tmp6 + tmp7;
103
104 /* The rotator is modified from fig 4-8 to avoid extra negations. */
105 z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */
106 z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */
107 z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */
108 z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */
109
110 z11 = tmp7 + z3; /* phase 5 */
111 z13 = tmp7 - z3;
112
113 dataptr[5] = z13 + z2; /* phase 6 */
114 dataptr[3] = z13 - z2;
115 dataptr[1] = z11 + z4;
116 dataptr[7] = z11 - z4;
117
118 dataptr += DCTSIZE; /* advance pointer to next row */
119 }
120
121 /* Pass 2: process columns. */
122
123 dataptr = data;
124 for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
125 tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];
126 tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];
127 tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];
128 tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];
129 tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];
130 tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];
131 tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];
132 tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];
133
134 /* Even part */
135
136 tmp10 = tmp0 + tmp3; /* phase 2 */
137 tmp13 = tmp0 - tmp3;
138 tmp11 = tmp1 + tmp2;
139 tmp12 = tmp1 - tmp2;
140
141 dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */
142 dataptr[DCTSIZE*4] = tmp10 - tmp11;
143
144 z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */
145 dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */
146 dataptr[DCTSIZE*6] = tmp13 - z1;
147
148 /* Odd part */
149
150 tmp10 = tmp4 + tmp5; /* phase 2 */
151 tmp11 = tmp5 + tmp6;
152 tmp12 = tmp6 + tmp7;
153
154 /* The rotator is modified from fig 4-8 to avoid extra negations. */
155 z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */
156 z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */
157 z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */
158 z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */
159
160 z11 = tmp7 + z3; /* phase 5 */
161 z13 = tmp7 - z3;
162
163 dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */
164 dataptr[DCTSIZE*3] = z13 - z2;
165 dataptr[DCTSIZE*1] = z11 + z4;
166 dataptr[DCTSIZE*7] = z11 - z4;
167
168 dataptr++; /* advance pointer to next column */
169 }
170}
171
172#endif /* DCT_FLOAT_SUPPORTED */
173