Line data Source code
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 0 : jpeg_fdct_float (FAST_FLOAT *data)
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 : 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 : }
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 : }
167 0 : }
168 :
169 : #endif /* DCT_FLOAT_SUPPORTED */
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