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 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 */
dataptr
int const JOCTET * dataptr
Definition: jpeglib.h:951
jpeglib.h
jinclude.h
GLOBAL
#define GLOBAL(type)
Definition: jmorecfg.h:188
jdct.h
data
JSAMPIMAGE data
Definition: jpeglib.h:945
DCTSIZE
#define DCTSIZE
Definition: jpeglib.h:41
code
Definition: inftrees.h:24
jpeg_fdct_float
jpeg_fdct_float(FAST_FLOAT *data)
Definition: jfdctflt.c:59


openhrp3
Author(s): AIST, General Robotix Inc., Nakamura Lab of Dept. of Mechano Informatics at University of Tokyo
autogenerated on Wed Sep 7 2022 02:51:03