jfdctfst.c
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1 /*
2  * jfdctfst.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 fast, not so accurate integer implementation of the
9  * forward DCT (Discrete Cosine Transform).
10  *
11  * A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT
12  * on each column. Direct algorithms are also available, but they are
13  * much more complex and seem not to be any faster when reduced to code.
14  *
15  * This implementation is based on Arai, Agui, and Nakajima's algorithm for
16  * scaled DCT. Their original paper (Trans. IEICE E-71(11):1095) is in
17  * Japanese, but the algorithm is described in the Pennebaker & Mitchell
18  * JPEG textbook (see REFERENCES section in file README). The following code
19  * is based directly on figure 4-8 in P&M.
20  * While an 8-point DCT cannot be done in less than 11 multiplies, it is
21  * possible to arrange the computation so that many of the multiplies are
22  * simple scalings of the final outputs. These multiplies can then be
23  * folded into the multiplications or divisions by the JPEG quantization
24  * table entries. The AA&N method leaves only 5 multiplies and 29 adds
25  * to be done in the DCT itself.
26  * The primary disadvantage of this method is that with fixed-point math,
27  * accuracy is lost due to imprecise representation of the scaled
28  * quantization values. The smaller the quantization table entry, the less
29  * precise the scaled value, so this implementation does worse with high-
30  * quality-setting files than with low-quality ones.
31  */
32 
33 #define JPEG_INTERNALS
34 #include "jinclude.h"
35 #include "jpeglib.h"
36 #include "jdct.h" /* Private declarations for DCT subsystem */
37 
38 #ifdef DCT_IFAST_SUPPORTED
39 
40 
41 /*
42  * This module is specialized to the case DCTSIZE = 8.
43  */
44 
45 #if DCTSIZE != 8
46  Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
47 #endif
48 
49 
50 /* Scaling decisions are generally the same as in the LL&M algorithm;
51  * see jfdctint.c for more details. However, we choose to descale
52  * (right shift) multiplication products as soon as they are formed,
53  * rather than carrying additional fractional bits into subsequent additions.
54  * This compromises accuracy slightly, but it lets us save a few shifts.
55  * More importantly, 16-bit arithmetic is then adequate (for 8-bit samples)
56  * everywhere except in the multiplications proper; this saves a good deal
57  * of work on 16-bit-int machines.
58  *
59  * Again to save a few shifts, the intermediate results between pass 1 and
60  * pass 2 are not upscaled, but are represented only to integral precision.
61  *
62  * A final compromise is to represent the multiplicative constants to only
63  * 8 fractional bits, rather than 13. This saves some shifting work on some
64  * machines, and may also reduce the cost of multiplication (since there
65  * are fewer one-bits in the constants).
66  */
67 
68 #define CONST_BITS 8
69 
70 
71 /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
72  * causing a lot of useless floating-point operations at run time.
73  * To get around this we use the following pre-calculated constants.
74  * If you change CONST_BITS you may want to add appropriate values.
75  * (With a reasonable C compiler, you can just rely on the FIX() macro...)
76  */
77 
78 #if CONST_BITS == 8
79 #define FIX_0_382683433 ((INT32) 98) /* FIX(0.382683433) */
80 #define FIX_0_541196100 ((INT32) 139) /* FIX(0.541196100) */
81 #define FIX_0_707106781 ((INT32) 181) /* FIX(0.707106781) */
82 #define FIX_1_306562965 ((INT32) 334) /* FIX(1.306562965) */
83 #else
84 #define FIX_0_382683433 FIX(0.382683433)
85 #define FIX_0_541196100 FIX(0.541196100)
86 #define FIX_0_707106781 FIX(0.707106781)
87 #define FIX_1_306562965 FIX(1.306562965)
88 #endif
89 
90 
91 /* We can gain a little more speed, with a further compromise in accuracy,
92  * by omitting the addition in a descaling shift. This yields an incorrectly
93  * rounded result half the time...
94  */
95 
96 #ifndef USE_ACCURATE_ROUNDING
97 #undef DESCALE
98 #define DESCALE(x,n) RIGHT_SHIFT(x, n)
99 #endif
100 
101 
102 /* Multiply a DCTELEM variable by an INT32 constant, and immediately
103  * descale to yield a DCTELEM result.
104  */
105 
106 #define MULTIPLY(var,const) ((DCTELEM) DESCALE((var) * (const), CONST_BITS))
107 
108 
109 /*
110  * Perform the forward DCT on one block of samples.
111  */
112 
113 GLOBAL(void)
115 {
116  DCTELEM tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
117  DCTELEM tmp10, tmp11, tmp12, tmp13;
118  DCTELEM z1, z2, z3, z4, z5, z11, z13;
119  DCTELEM *dataptr;
120  int ctr;
122 
123  /* Pass 1: process rows. */
124 
125  dataptr = data;
126  for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
127  tmp0 = dataptr[0] + dataptr[7];
128  tmp7 = dataptr[0] - dataptr[7];
129  tmp1 = dataptr[1] + dataptr[6];
130  tmp6 = dataptr[1] - dataptr[6];
131  tmp2 = dataptr[2] + dataptr[5];
132  tmp5 = dataptr[2] - dataptr[5];
133  tmp3 = dataptr[3] + dataptr[4];
134  tmp4 = dataptr[3] - dataptr[4];
135 
136  /* Even part */
137 
138  tmp10 = tmp0 + tmp3; /* phase 2 */
139  tmp13 = tmp0 - tmp3;
140  tmp11 = tmp1 + tmp2;
141  tmp12 = tmp1 - tmp2;
142 
143  dataptr[0] = tmp10 + tmp11; /* phase 3 */
144  dataptr[4] = tmp10 - tmp11;
145 
146  z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */
147  dataptr[2] = tmp13 + z1; /* phase 5 */
148  dataptr[6] = tmp13 - z1;
149 
150  /* Odd part */
151 
152  tmp10 = tmp4 + tmp5; /* phase 2 */
153  tmp11 = tmp5 + tmp6;
154  tmp12 = tmp6 + tmp7;
155 
156  /* The rotator is modified from fig 4-8 to avoid extra negations. */
157  z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */
158  z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */
159  z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */
160  z3 = MULTIPLY(tmp11, FIX_0_707106781); /* c4 */
161 
162  z11 = tmp7 + z3; /* phase 5 */
163  z13 = tmp7 - z3;
164 
165  dataptr[5] = z13 + z2; /* phase 6 */
166  dataptr[3] = z13 - z2;
167  dataptr[1] = z11 + z4;
168  dataptr[7] = z11 - z4;
169 
170  dataptr += DCTSIZE; /* advance pointer to next row */
171  }
172 
173  /* Pass 2: process columns. */
174 
175  dataptr = data;
176  for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
177  tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];
178  tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];
179  tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];
180  tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];
181  tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];
182  tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];
183  tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];
184  tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];
185 
186  /* Even part */
187 
188  tmp10 = tmp0 + tmp3; /* phase 2 */
189  tmp13 = tmp0 - tmp3;
190  tmp11 = tmp1 + tmp2;
191  tmp12 = tmp1 - tmp2;
192 
193  dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */
194  dataptr[DCTSIZE*4] = tmp10 - tmp11;
195 
196  z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */
197  dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */
198  dataptr[DCTSIZE*6] = tmp13 - z1;
199 
200  /* Odd part */
201 
202  tmp10 = tmp4 + tmp5; /* phase 2 */
203  tmp11 = tmp5 + tmp6;
204  tmp12 = tmp6 + tmp7;
205 
206  /* The rotator is modified from fig 4-8 to avoid extra negations. */
207  z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */
208  z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */
209  z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */
210  z3 = MULTIPLY(tmp11, FIX_0_707106781); /* c4 */
211 
212  z11 = tmp7 + z3; /* phase 5 */
213  z13 = tmp7 - z3;
214 
215  dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */
216  dataptr[DCTSIZE*3] = z13 - z2;
217  dataptr[DCTSIZE*1] = z11 + z4;
218  dataptr[DCTSIZE*7] = z11 - z4;
219 
220  dataptr++; /* advance pointer to next column */
221  }
222 }
223 
224 #endif /* DCT_IFAST_SUPPORTED */
INT32 DCTELEM
Definition: jdct.h:32
#define SHIFT_TEMPS
Definition: jpegint.h:289
#define FIX_0_382683433
Definition: jfdctfst.c:79
#define FIX_1_306562965
Definition: jfdctfst.c:82
#define MULTIPLY(var, const)
Definition: jfdctfst.c:106
Definition: inftrees.h:24
#define FIX_0_707106781
Definition: jfdctfst.c:81
#define GLOBAL(type)
Definition: jmorecfg.h:188
#define DCTSIZE
Definition: jpeglib.h:41
JSAMPIMAGE data
Definition: jpeglib.h:945
#define FIX_0_541196100
Definition: jfdctfst.c:80
int const JOCTET * dataptr
Definition: jpeglib.h:950
jpeg_fdct_ifast(DCTELEM *data)
Definition: jfdctfst.c:114


openhrp3
Author(s): AIST, General Robotix Inc., Nakamura Lab of Dept. of Mechano Informatics at University of Tokyo
autogenerated on Thu Sep 8 2022 02:24:04