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jfdctfst.c
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1 /*
2  * jfdctfst.c
3  *
4  * Copyright (C) 1994-1996, Thomas G. Lane.
5  * Modified 2003-2017 by Guido Vollbeding.
6  * This file is part of the Independent JPEG Group's software.
7  * For conditions of distribution and use, see the accompanying README file.
8  *
9  * This file contains a fast, not so accurate integer implementation of the
10  * forward DCT (Discrete Cosine Transform).
11  *
12  * A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT
13  * on each column. Direct algorithms are also available, but they are
14  * much more complex and seem not to be any faster when reduced to code.
15  *
16  * This implementation is based on Arai, Agui, and Nakajima's algorithm for
17  * scaled DCT. Their original paper (Trans. IEICE E-71(11):1095) is in
18  * Japanese, but the algorithm is described in the Pennebaker & Mitchell
19  * JPEG textbook (see REFERENCES section in file README). The following code
20  * is based directly on figure 4-8 in P&M.
21  * While an 8-point DCT cannot be done in less than 11 multiplies, it is
22  * possible to arrange the computation so that many of the multiplies are
23  * simple scalings of the final outputs. These multiplies can then be
24  * folded into the multiplications or divisions by the JPEG quantization
25  * table entries. The AA&N method leaves only 5 multiplies and 29 adds
26  * to be done in the DCT itself.
27  * The primary disadvantage of this method is that with fixed-point math,
28  * accuracy is lost due to imprecise representation of the scaled
29  * quantization values. The smaller the quantization table entry, the less
30  * precise the scaled value, so this implementation does worse with high-
31  * quality-setting files than with low-quality ones.
32  */
33 
34 #define JPEG_INTERNALS
35 #include "jinclude.h"
36 #include "jpeglib.h"
37 #include "jdct.h" /* Private declarations for DCT subsystem */
38 
39 #ifdef DCT_IFAST_SUPPORTED
40 
41 
42 /*
43  * This module is specialized to the case DCTSIZE = 8.
44  */
45 
46 #if DCTSIZE != 8
47  Sorry, this code only copes with 8x8 DCT blocks. /* deliberate syntax err */
48 #endif
49 
50 
51 /* Scaling decisions are generally the same as in the LL&M algorithm;
52  * see jfdctint.c for more details. However, we choose to descale
53  * (right shift) multiplication products as soon as they are formed,
54  * rather than carrying additional fractional bits into subsequent additions.
55  * This compromises accuracy slightly, but it lets us save a few shifts.
56  * More importantly, 16-bit arithmetic is then adequate (for 8-bit samples)
57  * everywhere except in the multiplications proper; this saves a good deal
58  * of work on 16-bit-int machines.
59  *
60  * Again to save a few shifts, the intermediate results between pass 1 and
61  * pass 2 are not upscaled, but are represented only to integral precision.
62  *
63  * A final compromise is to represent the multiplicative constants to only
64  * 8 fractional bits, rather than 13. This saves some shifting work on some
65  * machines, and may also reduce the cost of multiplication (since there
66  * are fewer one-bits in the constants).
67  */
68 
69 #define CONST_BITS 8
70 
71 
72 /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
73  * causing a lot of useless floating-point operations at run time.
74  * To get around this we use the following pre-calculated constants.
75  * If you change CONST_BITS you may want to add appropriate values.
76  * (With a reasonable C compiler, you can just rely on the FIX() macro...)
77  */
78 
79 #if CONST_BITS == 8
80 #define FIX_0_382683433 ((INT32) 98) /* FIX(0.382683433) */
81 #define FIX_0_541196100 ((INT32) 139) /* FIX(0.541196100) */
82 #define FIX_0_707106781 ((INT32) 181) /* FIX(0.707106781) */
83 #define FIX_1_306562965 ((INT32) 334) /* FIX(1.306562965) */
84 #else
85 #define FIX_0_382683433 FIX(0.382683433)
86 #define FIX_0_541196100 FIX(0.541196100)
87 #define FIX_0_707106781 FIX(0.707106781)
88 #define FIX_1_306562965 FIX(1.306562965)
89 #endif
90 
91 
92 /* We can gain a little more speed, with a further compromise in accuracy,
93  * by omitting the addition in a descaling shift. This yields an incorrectly
94  * rounded result half the time...
95  */
96 
97 #ifndef USE_ACCURATE_ROUNDING
98 #undef DESCALE
99 #define DESCALE(x,n) RIGHT_SHIFT(x, n)
100 #endif
101 
102 
103 /* Multiply a DCTELEM variable by an INT32 constant, and immediately
104  * descale to yield a DCTELEM result.
105  */
106 
107 #define MULTIPLY(var,const) ((DCTELEM) DESCALE((var) * (const), CONST_BITS))
108 
109 
110 /*
111  * Perform the forward DCT on one block of samples.
112  *
113  * cK represents cos(K*pi/16).
114  */
115 
116 GLOBAL(void)
118 {
119  DCTELEM tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
120  DCTELEM tmp10, tmp11, tmp12, tmp13;
121  DCTELEM z1, z2, z3, z4, z5, z11, z13;
122  DCTELEM *dataptr;
123  JSAMPROW elemptr;
124  int ctr;
126 
127  /* Pass 1: process rows. */
128 
129  dataptr = data;
130  for (ctr = 0; ctr < DCTSIZE; ctr++) {
131  elemptr = sample_data[ctr] + start_col;
132 
133  /* Load data into workspace */
134  tmp0 = GETJSAMPLE(elemptr[0]) + GETJSAMPLE(elemptr[7]);
135  tmp7 = GETJSAMPLE(elemptr[0]) - GETJSAMPLE(elemptr[7]);
136  tmp1 = GETJSAMPLE(elemptr[1]) + GETJSAMPLE(elemptr[6]);
137  tmp6 = GETJSAMPLE(elemptr[1]) - GETJSAMPLE(elemptr[6]);
138  tmp2 = GETJSAMPLE(elemptr[2]) + GETJSAMPLE(elemptr[5]);
139  tmp5 = GETJSAMPLE(elemptr[2]) - GETJSAMPLE(elemptr[5]);
140  tmp3 = GETJSAMPLE(elemptr[3]) + GETJSAMPLE(elemptr[4]);
141  tmp4 = GETJSAMPLE(elemptr[3]) - GETJSAMPLE(elemptr[4]);
142 
143  /* Even part */
144 
145  tmp10 = tmp0 + tmp3; /* phase 2 */
146  tmp13 = tmp0 - tmp3;
147  tmp11 = tmp1 + tmp2;
148  tmp12 = tmp1 - tmp2;
149 
150  /* Apply unsigned->signed conversion. */
151  dataptr[0] = tmp10 + tmp11 - 8 * CENTERJSAMPLE; /* phase 3 */
152  dataptr[4] = tmp10 - tmp11;
153 
154  z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */
155  dataptr[2] = tmp13 + z1; /* phase 5 */
156  dataptr[6] = tmp13 - z1;
157 
158  /* Odd part */
159 
160  tmp10 = tmp4 + tmp5; /* phase 2 */
161  tmp11 = tmp5 + tmp6;
162  tmp12 = tmp6 + tmp7;
163 
164  /* The rotator is modified from fig 4-8 to avoid extra negations. */
165  z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */
166  z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */
167  z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */
168  z3 = MULTIPLY(tmp11, FIX_0_707106781); /* c4 */
169 
170  z11 = tmp7 + z3; /* phase 5 */
171  z13 = tmp7 - z3;
172 
173  dataptr[5] = z13 + z2; /* phase 6 */
174  dataptr[3] = z13 - z2;
175  dataptr[1] = z11 + z4;
176  dataptr[7] = z11 - z4;
177 
178  dataptr += DCTSIZE; /* advance pointer to next row */
179  }
180 
181  /* Pass 2: process columns. */
182 
183  dataptr = data;
184  for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
185  tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];
186  tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];
187  tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];
188  tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];
189  tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];
190  tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];
191  tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];
192  tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];
193 
194  /* Even part */
195 
196  tmp10 = tmp0 + tmp3; /* phase 2 */
197  tmp13 = tmp0 - tmp3;
198  tmp11 = tmp1 + tmp2;
199  tmp12 = tmp1 - tmp2;
200 
201  dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */
202  dataptr[DCTSIZE*4] = tmp10 - tmp11;
203 
204  z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */
205  dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */
206  dataptr[DCTSIZE*6] = tmp13 - z1;
207 
208  /* Odd part */
209 
210  tmp10 = tmp4 + tmp5; /* phase 2 */
211  tmp11 = tmp5 + tmp6;
212  tmp12 = tmp6 + tmp7;
213 
214  /* The rotator is modified from fig 4-8 to avoid extra negations. */
215  z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */
216  z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */
217  z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */
218  z3 = MULTIPLY(tmp11, FIX_0_707106781); /* c4 */
219 
220  z11 = tmp7 + z3; /* phase 5 */
221  z13 = tmp7 - z3;
222 
223  dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */
224  dataptr[DCTSIZE*3] = z13 - z2;
225  dataptr[DCTSIZE*1] = z11 + z4;
226  dataptr[DCTSIZE*7] = z11 - z4;
227 
228  dataptr++; /* advance pointer to next column */
229  }
230 }
231 
232 #endif /* DCT_IFAST_SUPPORTED */
#define CENTERJSAMPLE
Definition: jmorecfg.h:84
JSAMPLE FAR * JSAMPROW
Definition: jpeglib.h:75
JSAMPARRAY JDIMENSION start_col
Definition: jdct.h:169
INT32 DCTELEM
Definition: jdct.h:38
#define GETJSAMPLE(value)
Definition: jmorecfg.h:78
#define SHIFT_TEMPS
Definition: jpegint.h:301
static int blocks
Definition: mkdosfs.c:527
GLint GLenum GLsizei GLsizei GLsizei GLint GLsizei const GLvoid * data
Definition: gl.h:1950
JSAMPROW * JSAMPARRAY
Definition: jpeglib.h:76
#define GLOBAL(type)
Definition: jmorecfg.h:291
#define DCTSIZE
Definition: jpeglib.h:50
unsigned int JDIMENSION
Definition: jmorecfg.h:229
int const JOCTET * dataptr
Definition: jpeglib.h:1027
JSAMPARRAY sample_data
Definition: jdct.h:169
Sorry
Definition: jdcolor.c:19