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comparison mupdf-source/thirdparty/libjpeg/jfdctflt.c @ 2:b50eed0cc0ef upstream

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ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4. The directory name has changed: no version number in the expanded directory now.
author Franz Glasner <fzglas.hg@dom66.de>
date Mon, 15 Sep 2025 11:43:07 +0200
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1:1d09e1dec1d9 2:b50eed0cc0ef
1 /*
2 * jfdctflt.c
3 *
4 * Copyright (C) 1994-1996, Thomas G. Lane.
5 * Modified 2003-2017 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 DCT blocks. /* deliberate syntax err */
52 #endif
53
54
55 /*
56 * Perform the forward DCT on one block of samples.
57 *
58 * cK represents cos(K*pi/16).
59 */
60
61 GLOBAL(void)
62 jpeg_fdct_float (FAST_FLOAT * data, JSAMPARRAY sample_data, JDIMENSION start_col)
63 {
64 FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
65 FAST_FLOAT tmp10, tmp11, tmp12, tmp13;
66 FAST_FLOAT z1, z2, z3, z4, z5, z11, z13;
67 FAST_FLOAT *dataptr;
68 JSAMPROW elemptr;
69 int ctr;
70
71 /* Pass 1: process rows. */
72
73 dataptr = data;
74 for (ctr = 0; ctr < DCTSIZE; ctr++) {
75 elemptr = sample_data[ctr] + start_col;
76
77 /* Load data into workspace */
78 tmp0 = (FAST_FLOAT) (GETJSAMPLE(elemptr[0]) + GETJSAMPLE(elemptr[7]));
79 tmp7 = (FAST_FLOAT) (GETJSAMPLE(elemptr[0]) - GETJSAMPLE(elemptr[7]));
80 tmp1 = (FAST_FLOAT) (GETJSAMPLE(elemptr[1]) + GETJSAMPLE(elemptr[6]));
81 tmp6 = (FAST_FLOAT) (GETJSAMPLE(elemptr[1]) - GETJSAMPLE(elemptr[6]));
82 tmp2 = (FAST_FLOAT) (GETJSAMPLE(elemptr[2]) + GETJSAMPLE(elemptr[5]));
83 tmp5 = (FAST_FLOAT) (GETJSAMPLE(elemptr[2]) - GETJSAMPLE(elemptr[5]));
84 tmp3 = (FAST_FLOAT) (GETJSAMPLE(elemptr[3]) + GETJSAMPLE(elemptr[4]));
85 tmp4 = (FAST_FLOAT) (GETJSAMPLE(elemptr[3]) - GETJSAMPLE(elemptr[4]));
86
87 /* Even part */
88
89 tmp10 = tmp0 + tmp3; /* phase 2 */
90 tmp13 = tmp0 - tmp3;
91 tmp11 = tmp1 + tmp2;
92 tmp12 = tmp1 - tmp2;
93
94 /* Apply unsigned->signed conversion. */
95 dataptr[0] = tmp10 + tmp11 - 8 * CENTERJSAMPLE; /* phase 3 */
96 dataptr[4] = tmp10 - tmp11;
97
98 z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */
99 dataptr[2] = tmp13 + z1; /* phase 5 */
100 dataptr[6] = tmp13 - z1;
101
102 /* Odd part */
103
104 tmp10 = tmp4 + tmp5; /* phase 2 */
105 tmp11 = tmp5 + tmp6;
106 tmp12 = tmp6 + tmp7;
107
108 /* The rotator is modified from fig 4-8 to avoid extra negations. */
109 z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */
110 z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */
111 z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */
112 z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */
113
114 z11 = tmp7 + z3; /* phase 5 */
115 z13 = tmp7 - z3;
116
117 dataptr[5] = z13 + z2; /* phase 6 */
118 dataptr[3] = z13 - z2;
119 dataptr[1] = z11 + z4;
120 dataptr[7] = z11 - z4;
121
122 dataptr += DCTSIZE; /* advance pointer to next row */
123 }
124
125 /* Pass 2: process columns. */
126
127 dataptr = data;
128 for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
129 tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];
130 tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];
131 tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];
132 tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];
133 tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];
134 tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];
135 tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];
136 tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];
137
138 /* Even part */
139
140 tmp10 = tmp0 + tmp3; /* phase 2 */
141 tmp13 = tmp0 - tmp3;
142 tmp11 = tmp1 + tmp2;
143 tmp12 = tmp1 - tmp2;
144
145 dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */
146 dataptr[DCTSIZE*4] = tmp10 - tmp11;
147
148 z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */
149 dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */
150 dataptr[DCTSIZE*6] = tmp13 - z1;
151
152 /* Odd part */
153
154 tmp10 = tmp4 + tmp5; /* phase 2 */
155 tmp11 = tmp5 + tmp6;
156 tmp12 = tmp6 + tmp7;
157
158 /* The rotator is modified from fig 4-8 to avoid extra negations. */
159 z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */
160 z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */
161 z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */
162 z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */
163
164 z11 = tmp7 + z3; /* phase 5 */
165 z13 = tmp7 - z3;
166
167 dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */
168 dataptr[DCTSIZE*3] = z13 - z2;
169 dataptr[DCTSIZE*1] = z11 + z4;
170 dataptr[DCTSIZE*7] = z11 - z4;
171
172 dataptr++; /* advance pointer to next column */
173 }
174 }
175
176 #endif /* DCT_FLOAT_SUPPORTED */