/src/libjpeg-turbo.main/jfdctflt.c
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1 | | /* |
2 | | * jfdctflt.c |
3 | | * |
4 | | * Copyright (C) 1994-1996, Thomas G. Lane. |
5 | | * This file is part of the Independent JPEG Group's software. |
6 | | * For conditions of distribution and use, see the accompanying README.ijg |
7 | | * 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.ijg). The following |
25 | | * code 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 | | |
59 | | GLOBAL(void) |
60 | | jpeg_fdct_float(FAST_FLOAT *data) |
61 | 0 | { |
62 | 0 | FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7; |
63 | 0 | FAST_FLOAT tmp10, tmp11, tmp12, tmp13; |
64 | 0 | FAST_FLOAT z1, z2, z3, z4, z5, z11, z13; |
65 | 0 | FAST_FLOAT *dataptr; |
66 | 0 | int ctr; |
67 | | |
68 | | /* Pass 1: process rows. */ |
69 | |
|
70 | 0 | dataptr = data; |
71 | 0 | for (ctr = DCTSIZE - 1; ctr >= 0; ctr--) { |
72 | 0 | tmp0 = dataptr[0] + dataptr[7]; |
73 | 0 | tmp7 = dataptr[0] - dataptr[7]; |
74 | 0 | tmp1 = dataptr[1] + dataptr[6]; |
75 | 0 | tmp6 = dataptr[1] - dataptr[6]; |
76 | 0 | tmp2 = dataptr[2] + dataptr[5]; |
77 | 0 | tmp5 = dataptr[2] - dataptr[5]; |
78 | 0 | tmp3 = dataptr[3] + dataptr[4]; |
79 | 0 | tmp4 = dataptr[3] - dataptr[4]; |
80 | | |
81 | | /* Even part */ |
82 | |
|
83 | 0 | tmp10 = tmp0 + tmp3; /* phase 2 */ |
84 | 0 | tmp13 = tmp0 - tmp3; |
85 | 0 | tmp11 = tmp1 + tmp2; |
86 | 0 | tmp12 = tmp1 - tmp2; |
87 | |
|
88 | 0 | dataptr[0] = tmp10 + tmp11; /* phase 3 */ |
89 | 0 | dataptr[4] = tmp10 - tmp11; |
90 | |
|
91 | 0 | z1 = (tmp12 + tmp13) * ((FAST_FLOAT)0.707106781); /* c4 */ |
92 | 0 | dataptr[2] = tmp13 + z1; /* phase 5 */ |
93 | 0 | dataptr[6] = tmp13 - z1; |
94 | | |
95 | | /* Odd part */ |
96 | |
|
97 | 0 | tmp10 = tmp4 + tmp5; /* phase 2 */ |
98 | 0 | tmp11 = tmp5 + tmp6; |
99 | 0 | tmp12 = tmp6 + tmp7; |
100 | | |
101 | | /* The rotator is modified from fig 4-8 to avoid extra negations. */ |
102 | 0 | z5 = (tmp10 - tmp12) * ((FAST_FLOAT)0.382683433); /* c6 */ |
103 | 0 | z2 = ((FAST_FLOAT)0.541196100) * tmp10 + z5; /* c2-c6 */ |
104 | 0 | z4 = ((FAST_FLOAT)1.306562965) * tmp12 + z5; /* c2+c6 */ |
105 | 0 | z3 = tmp11 * ((FAST_FLOAT)0.707106781); /* c4 */ |
106 | |
|
107 | 0 | z11 = tmp7 + z3; /* phase 5 */ |
108 | 0 | z13 = tmp7 - z3; |
109 | |
|
110 | 0 | dataptr[5] = z13 + z2; /* phase 6 */ |
111 | 0 | dataptr[3] = z13 - z2; |
112 | 0 | dataptr[1] = z11 + z4; |
113 | 0 | dataptr[7] = z11 - z4; |
114 | |
|
115 | 0 | dataptr += DCTSIZE; /* advance pointer to next row */ |
116 | 0 | } |
117 | | |
118 | | /* Pass 2: process columns. */ |
119 | |
|
120 | 0 | dataptr = data; |
121 | 0 | for (ctr = DCTSIZE - 1; ctr >= 0; ctr--) { |
122 | 0 | tmp0 = dataptr[DCTSIZE * 0] + dataptr[DCTSIZE * 7]; |
123 | 0 | tmp7 = dataptr[DCTSIZE * 0] - dataptr[DCTSIZE * 7]; |
124 | 0 | tmp1 = dataptr[DCTSIZE * 1] + dataptr[DCTSIZE * 6]; |
125 | 0 | tmp6 = dataptr[DCTSIZE * 1] - dataptr[DCTSIZE * 6]; |
126 | 0 | tmp2 = dataptr[DCTSIZE * 2] + dataptr[DCTSIZE * 5]; |
127 | 0 | tmp5 = dataptr[DCTSIZE * 2] - dataptr[DCTSIZE * 5]; |
128 | 0 | tmp3 = dataptr[DCTSIZE * 3] + dataptr[DCTSIZE * 4]; |
129 | 0 | tmp4 = dataptr[DCTSIZE * 3] - dataptr[DCTSIZE * 4]; |
130 | | |
131 | | /* Even part */ |
132 | |
|
133 | 0 | tmp10 = tmp0 + tmp3; /* phase 2 */ |
134 | 0 | tmp13 = tmp0 - tmp3; |
135 | 0 | tmp11 = tmp1 + tmp2; |
136 | 0 | tmp12 = tmp1 - tmp2; |
137 | |
|
138 | 0 | dataptr[DCTSIZE * 0] = tmp10 + tmp11; /* phase 3 */ |
139 | 0 | dataptr[DCTSIZE * 4] = tmp10 - tmp11; |
140 | |
|
141 | 0 | z1 = (tmp12 + tmp13) * ((FAST_FLOAT)0.707106781); /* c4 */ |
142 | 0 | dataptr[DCTSIZE * 2] = tmp13 + z1; /* phase 5 */ |
143 | 0 | dataptr[DCTSIZE * 6] = tmp13 - z1; |
144 | | |
145 | | /* Odd part */ |
146 | |
|
147 | 0 | tmp10 = tmp4 + tmp5; /* phase 2 */ |
148 | 0 | tmp11 = tmp5 + tmp6; |
149 | 0 | tmp12 = tmp6 + tmp7; |
150 | | |
151 | | /* The rotator is modified from fig 4-8 to avoid extra negations. */ |
152 | 0 | z5 = (tmp10 - tmp12) * ((FAST_FLOAT)0.382683433); /* c6 */ |
153 | 0 | z2 = ((FAST_FLOAT)0.541196100) * tmp10 + z5; /* c2-c6 */ |
154 | 0 | z4 = ((FAST_FLOAT)1.306562965) * tmp12 + z5; /* c2+c6 */ |
155 | 0 | z3 = tmp11 * ((FAST_FLOAT)0.707106781); /* c4 */ |
156 | |
|
157 | 0 | z11 = tmp7 + z3; /* phase 5 */ |
158 | 0 | z13 = tmp7 - z3; |
159 | |
|
160 | 0 | dataptr[DCTSIZE * 5] = z13 + z2; /* phase 6 */ |
161 | 0 | dataptr[DCTSIZE * 3] = z13 - z2; |
162 | 0 | dataptr[DCTSIZE * 1] = z11 + z4; |
163 | 0 | dataptr[DCTSIZE * 7] = z11 - z4; |
164 | |
|
165 | 0 | dataptr++; /* advance pointer to next column */ |
166 | 0 | } |
167 | 0 | } |
168 | | |
169 | | #endif /* DCT_FLOAT_SUPPORTED */ |