jidctflt.c
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1 /*
2  * jidctflt.c
3  *
4  * Copyright (C) 1994-1998, 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  * inverse DCT (Discrete Cosine Transform). In the IJG code, this routine
10  * must also perform dequantization of the input coefficients.
11  *
12  * This implementation should be more accurate than either of the integer
13  * IDCT 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 IDCT can be done by 1-D IDCT on each column followed by 1-D IDCT
18  * on each row (or vice versa, but it's more convenient to emit a row at
19  * a time). Direct algorithms are also available, but they are much more
20  * complex and seem not to be any faster when reduced to code.
21  *
22  * This implementation is based on Arai, Agui, and Nakajima's algorithm for
23  * scaled DCT. Their original paper (Trans. IEICE E-71(11):1095) is in
24  * Japanese, but the algorithm is described in the Pennebaker & Mitchell
25  * JPEG textbook (see REFERENCES section in file README). The following code
26  * is based directly on figure 4-8 in P&M.
27  * While an 8-point DCT cannot be done in less than 11 multiplies, it is
28  * possible to arrange the computation so that many of the multiplies are
29  * simple scalings of the final outputs. These multiplies can then be
30  * folded into the multiplications or divisions by the JPEG quantization
31  * table entries. The AA&N method leaves only 5 multiplies and 29 adds
32  * to be done in the DCT itself.
33  * The primary disadvantage of this method is that with a fixed-point
34  * implementation, accuracy is lost due to imprecise representation of the
35  * scaled quantization values. However, that problem does not arise if
36  * we use floating point arithmetic.
37  */
38 
39 #define JPEG_INTERNALS
40 #include "jinclude.h"
41 #include "jpeglib.h"
42 #include "jdct.h" /* Private declarations for DCT subsystem */
43 
44 #ifdef DCT_FLOAT_SUPPORTED
45 
46 
47 /*
48  * This module is specialized to the case DCTSIZE = 8.
49  */
50 
51 #if DCTSIZE != 8
52  Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
53 #endif
54 
55 
56 /* Dequantize a coefficient by multiplying it by the multiplier-table
57  * entry; produce a float result.
58  */
59 
60 #define DEQUANTIZE(coef,quantval) (((FAST_FLOAT) (coef)) * (quantval))
61 
62 
63 /*
64  * Perform dequantization and inverse DCT on one block of coefficients.
65  */
66 
67 GLOBAL(void)
71 {
72  FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
73  FAST_FLOAT tmp10, tmp11, tmp12, tmp13;
74  FAST_FLOAT z5, z10, z11, z12, z13;
75  JCOEFPTR inptr;
76  FLOAT_MULT_TYPE * quantptr;
77  FAST_FLOAT * wsptr;
78  JSAMPROW outptr;
79  JSAMPLE *range_limit = IDCT_range_limit(cinfo);
80  int ctr;
81  FAST_FLOAT workspace[DCTSIZE2]; /* buffers data between passes */
83 
84  /* Pass 1: process columns from input, store into work array. */
85 
86  inptr = coef_block;
87  quantptr = (FLOAT_MULT_TYPE *) compptr->dct_table;
88  wsptr = workspace;
89  for (ctr = DCTSIZE; ctr > 0; ctr--) {
90  /* Due to quantization, we will usually find that many of the input
91  * coefficients are zero, especially the AC terms. We can exploit this
92  * by short-circuiting the IDCT calculation for any column in which all
93  * the AC terms are zero. In that case each output is equal to the
94  * DC coefficient (with scale factor as needed).
95  * With typical images and quantization tables, half or more of the
96  * column DCT calculations can be simplified this way.
97  */
98 
99  if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 &&
100  inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*4] == 0 &&
101  inptr[DCTSIZE*5] == 0 && inptr[DCTSIZE*6] == 0 &&
102  inptr[DCTSIZE*7] == 0) {
103  /* AC terms all zero */
104  FAST_FLOAT dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
105 
106  wsptr[DCTSIZE*0] = dcval;
107  wsptr[DCTSIZE*1] = dcval;
108  wsptr[DCTSIZE*2] = dcval;
109  wsptr[DCTSIZE*3] = dcval;
110  wsptr[DCTSIZE*4] = dcval;
111  wsptr[DCTSIZE*5] = dcval;
112  wsptr[DCTSIZE*6] = dcval;
113  wsptr[DCTSIZE*7] = dcval;
114 
115  inptr++; /* advance pointers to next column */
116  quantptr++;
117  wsptr++;
118  continue;
119  }
120 
121  /* Even part */
122 
123  tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
124  tmp1 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
125  tmp2 = DEQUANTIZE(inptr[DCTSIZE*4], quantptr[DCTSIZE*4]);
126  tmp3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);
127 
128  tmp10 = tmp0 + tmp2; /* phase 3 */
129  tmp11 = tmp0 - tmp2;
130 
131  tmp13 = tmp1 + tmp3; /* phases 5-3 */
132  tmp12 = (tmp1 - tmp3) * ((FAST_FLOAT) 1.414213562) - tmp13; /* 2*c4 */
133 
134  tmp0 = tmp10 + tmp13; /* phase 2 */
135  tmp3 = tmp10 - tmp13;
136  tmp1 = tmp11 + tmp12;
137  tmp2 = tmp11 - tmp12;
138 
139  /* Odd part */
140 
141  tmp4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
142  tmp5 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
143  tmp6 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
144  tmp7 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
145 
146  z13 = tmp6 + tmp5; /* phase 6 */
147  z10 = tmp6 - tmp5;
148  z11 = tmp4 + tmp7;
149  z12 = tmp4 - tmp7;
150 
151  tmp7 = z11 + z13; /* phase 5 */
152  tmp11 = (z11 - z13) * ((FAST_FLOAT) 1.414213562); /* 2*c4 */
153 
154  z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2*c2 */
155  tmp10 = ((FAST_FLOAT) 1.082392200) * z12 - z5; /* 2*(c2-c6) */
156  tmp12 = ((FAST_FLOAT) -2.613125930) * z10 + z5; /* -2*(c2+c6) */
157 
158  tmp6 = tmp12 - tmp7; /* phase 2 */
159  tmp5 = tmp11 - tmp6;
160  tmp4 = tmp10 + tmp5;
161 
162  wsptr[DCTSIZE*0] = tmp0 + tmp7;
163  wsptr[DCTSIZE*7] = tmp0 - tmp7;
164  wsptr[DCTSIZE*1] = tmp1 + tmp6;
165  wsptr[DCTSIZE*6] = tmp1 - tmp6;
166  wsptr[DCTSIZE*2] = tmp2 + tmp5;
167  wsptr[DCTSIZE*5] = tmp2 - tmp5;
168  wsptr[DCTSIZE*4] = tmp3 + tmp4;
169  wsptr[DCTSIZE*3] = tmp3 - tmp4;
170 
171  inptr++; /* advance pointers to next column */
172  quantptr++;
173  wsptr++;
174  }
175 
176  /* Pass 2: process rows from work array, store into output array. */
177  /* Note that we must descale the results by a factor of 8 == 2**3. */
178 
179  wsptr = workspace;
180  for (ctr = 0; ctr < DCTSIZE; ctr++) {
181  outptr = output_buf[ctr] + output_col;
182  /* Rows of zeroes can be exploited in the same way as we did with columns.
183  * However, the column calculation has created many nonzero AC terms, so
184  * the simplification applies less often (typically 5% to 10% of the time).
185  * And testing floats for zero is relatively expensive, so we don't bother.
186  */
187 
188  /* Even part */
189 
190  tmp10 = wsptr[0] + wsptr[4];
191  tmp11 = wsptr[0] - wsptr[4];
192 
193  tmp13 = wsptr[2] + wsptr[6];
194  tmp12 = (wsptr[2] - wsptr[6]) * ((FAST_FLOAT) 1.414213562) - tmp13;
195 
196  tmp0 = tmp10 + tmp13;
197  tmp3 = tmp10 - tmp13;
198  tmp1 = tmp11 + tmp12;
199  tmp2 = tmp11 - tmp12;
200 
201  /* Odd part */
202 
203  z13 = wsptr[5] + wsptr[3];
204  z10 = wsptr[5] - wsptr[3];
205  z11 = wsptr[1] + wsptr[7];
206  z12 = wsptr[1] - wsptr[7];
207 
208  tmp7 = z11 + z13;
209  tmp11 = (z11 - z13) * ((FAST_FLOAT) 1.414213562);
210 
211  z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2*c2 */
212  tmp10 = ((FAST_FLOAT) 1.082392200) * z12 - z5; /* 2*(c2-c6) */
213  tmp12 = ((FAST_FLOAT) -2.613125930) * z10 + z5; /* -2*(c2+c6) */
214 
215  tmp6 = tmp12 - tmp7;
216  tmp5 = tmp11 - tmp6;
217  tmp4 = tmp10 + tmp5;
218 
219  /* Final output stage: scale down by a factor of 8 and range-limit */
220 
221  outptr[0] = range_limit[(int) DESCALE((INT32) (tmp0 + tmp7), 3)
222  & RANGE_MASK];
223  outptr[7] = range_limit[(int) DESCALE((INT32) (tmp0 - tmp7), 3)
224  & RANGE_MASK];
225  outptr[1] = range_limit[(int) DESCALE((INT32) (tmp1 + tmp6), 3)
226  & RANGE_MASK];
227  outptr[6] = range_limit[(int) DESCALE((INT32) (tmp1 - tmp6), 3)
228  & RANGE_MASK];
229  outptr[2] = range_limit[(int) DESCALE((INT32) (tmp2 + tmp5), 3)
230  & RANGE_MASK];
231  outptr[5] = range_limit[(int) DESCALE((INT32) (tmp2 - tmp5), 3)
232  & RANGE_MASK];
233  outptr[4] = range_limit[(int) DESCALE((INT32) (tmp3 + tmp4), 3)
234  & RANGE_MASK];
235  outptr[3] = range_limit[(int) DESCALE((INT32) (tmp3 - tmp4), 3)
236  & RANGE_MASK];
237 
238  wsptr += DCTSIZE; /* advance pointer to next row */
239  }
240 }
241 
242 #endif /* DCT_FLOAT_SUPPORTED */
#define DESCALE(x, n)
Definition: jdct.h:146
#define IDCT_range_limit(cinfo)
Definition: jdct.h:76
char JSAMPLE
Definition: jmorecfg.h:64
JSAMPLE FAR * JSAMPROW
Definition: jpeglib.h:66
jpeg_component_info JCOEFPTR coef_block
Definition: jdct.h:102
#define RANGE_MASK
Definition: jdct.h:78
long INT32
Definition: jmorecfg.h:161
#define SHIFT_TEMPS
Definition: jpegint.h:289
#define for
jpeg_component_info * compptr
Definition: jdct.h:102
jpeg_component_info JCOEFPTR JSAMPARRAY JDIMENSION output_col
Definition: jdct.h:102
#define DCTSIZE2
Definition: jpeglib.h:42
JCOEF FAR * JCOEFPTR
Definition: jpeglib.h:75
FAST_FLOAT FLOAT_MULT_TYPE
Definition: jdct.h:64
Definition: inftrees.h:24
JSAMPROW * JSAMPARRAY
Definition: jpeglib.h:67
typedef int
Definition: png.h:1113
#define GLOBAL(type)
Definition: jmorecfg.h:188
#define DCTSIZE
Definition: jpeglib.h:41
jpeg_component_info JCOEFPTR JSAMPARRAY output_buf
Definition: jdct.h:102
unsigned int JDIMENSION
Definition: jmorecfg.h:171
jpeg_idct_float(j_decompress_ptr cinfo, jpeg_component_info *compptr, JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)
Definition: jidctflt.c:68
#define DEQUANTIZE(coef, quantval)
Definition: jidctflt.c:60


openhrp3
Author(s): AIST, General Robotix Inc., Nakamura Lab of Dept. of Mechano Informatics at University of Tokyo
autogenerated on Sat Apr 13 2019 02:14:23