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