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
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)
68 jpeg_idct_float (j_decompress_ptr cinfo, jpeg_component_info * compptr,
69 JCOEFPTR coef_block,
70 JSAMPARRAY output_buf, JDIMENSION output_col)
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 */
82 SHIFT_TEMPS
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) {
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 */
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1 /*
2 * jidctflt.c
3 *
4 * Copyright (C) 1994-1998, Thomas G. Lane.
5 * Modified 2010-2017 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 floating-point implementation of the
10 * inverse DCT (Discrete Cosine Transform). In the IJG code, this routine
11 * must also perform dequantization of the input coefficients.
12 *
13 * This implementation should be more accurate than either of the integer
14 * IDCT implementations. However, it may not give the same results on all
15 * machines because of differences in roundoff behavior. Speed will depend
16 * on the hardware's floating point capacity.
17 *
18 * A 2-D IDCT can be done by 1-D IDCT on each column followed by 1-D IDCT
19 * on each row (or vice versa, but it's more convenient to emit a row at
20 * a time). Direct algorithms are also available, but they are much more
21 * complex and seem not to be any faster when reduced to code.
22 *
23 * This implementation is based on Arai, Agui, and Nakajima's algorithm for
24 * scaled DCT. Their original paper (Trans. IEICE E-71(11):1095) is in
25 * Japanese, but the algorithm is described in the Pennebaker & Mitchell
33 * to be done in the DCT itself.
34 * The primary disadvantage of this method is that with a fixed-point
35 * implementation, accuracy is lost due to imprecise representation of the
36 * scaled quantization values. However, that problem does not arise if
37 * we use floating point arithmetic.
38 */
39
40 #define JPEG_INTERNALS
41 #include "jinclude.h"
42 #include "jpeglib.h"
43 #include "jdct.h" /* Private declarations for DCT subsystem */
44
45 #ifdef DCT_FLOAT_SUPPORTED
46
47
48 /*
49 * This module is specialized to the case DCTSIZE = 8.
50 */
51
52 #if DCTSIZE != 8
53 Sorry, this code only copes with 8x8 DCT blocks. /* deliberate syntax err */
54 #endif
55
56
57 /* Dequantize a coefficient by multiplying it by the multiplier-table
58 * entry; produce a float result.
59 */
60
61 #define DEQUANTIZE(coef,quantval) (((FAST_FLOAT) (coef)) * (quantval))
62
63
64 /*
65 * Perform dequantization and inverse DCT on one block of coefficients.
66 *
67 * cK represents cos(K*pi/16).
68 */
69
70 GLOBAL(void)
71 jpeg_idct_float (j_decompress_ptr cinfo, jpeg_component_info * compptr,
72 JCOEFPTR coef_block,
73 JSAMPARRAY output_buf, JDIMENSION output_col)
74 {
75 FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
76 FAST_FLOAT tmp10, tmp11, tmp12, tmp13;
77 FAST_FLOAT z5, z10, z11, z12, z13;
78 JCOEFPTR inptr;
79 FLOAT_MULT_TYPE * quantptr;
80 FAST_FLOAT * wsptr;
81 JSAMPROW outptr;
82 JSAMPLE *range_limit = IDCT_range_limit(cinfo);
83 int ctr;
84 FAST_FLOAT workspace[DCTSIZE2]; /* buffers data between passes */
85
86 /* Pass 1: process columns from input, store into work array. */
87
88 inptr = coef_block;
89 quantptr = (FLOAT_MULT_TYPE *) compptr->dct_table;
90 wsptr = workspace;
91 for (ctr = DCTSIZE; ctr > 0; ctr--) {
92 /* Due to quantization, we will usually find that many of the input
93 * coefficients are zero, especially the AC terms. We can exploit this
94 * by short-circuiting the IDCT calculation for any column in which all
95 * the AC terms are zero. In that case each output is equal to the
96 * DC coefficient (with scale factor as needed).
97 * With typical images and quantization tables, half or more of the
98 * column DCT calculations can be simplified this way.
99 */
100
101 if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 &&
102 inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*4] == 0 &&
103 inptr[DCTSIZE*5] == 0 && inptr[DCTSIZE*6] == 0 &&
104 inptr[DCTSIZE*7] == 0) {
137 tmp3 = tmp10 - tmp13;
138 tmp1 = tmp11 + tmp12;
139 tmp2 = tmp11 - tmp12;
140
141 /* Odd part */
142
143 tmp4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
144 tmp5 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
145 tmp6 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
146 tmp7 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
147
148 z13 = tmp6 + tmp5; /* phase 6 */
149 z10 = tmp6 - tmp5;
150 z11 = tmp4 + tmp7;
151 z12 = tmp4 - tmp7;
152
153 tmp7 = z11 + z13; /* phase 5 */
154 tmp11 = (z11 - z13) * ((FAST_FLOAT) 1.414213562); /* 2*c4 */
155
156 z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2*c2 */
157 tmp10 = z5 - z12 * ((FAST_FLOAT) 1.082392200); /* 2*(c2-c6) */
158 tmp12 = z5 - z10 * ((FAST_FLOAT) 2.613125930); /* 2*(c2+c6) */
159
160 tmp6 = tmp12 - tmp7; /* phase 2 */
161 tmp5 = tmp11 - tmp6;
162 tmp4 = tmp10 - tmp5;
163
164 wsptr[DCTSIZE*0] = tmp0 + tmp7;
165 wsptr[DCTSIZE*7] = tmp0 - tmp7;
166 wsptr[DCTSIZE*1] = tmp1 + tmp6;
167 wsptr[DCTSIZE*6] = tmp1 - tmp6;
168 wsptr[DCTSIZE*2] = tmp2 + tmp5;
169 wsptr[DCTSIZE*5] = tmp2 - tmp5;
170 wsptr[DCTSIZE*3] = tmp3 + tmp4;
171 wsptr[DCTSIZE*4] = tmp3 - tmp4;
172
173 inptr++; /* advance pointers to next column */
174 quantptr++;
175 wsptr++;
176 }
177
178 /* Pass 2: process rows from work array, store into output array. */
179
180 wsptr = workspace;
181 for (ctr = 0; ctr < DCTSIZE; ctr++) {
182 outptr = output_buf[ctr] + output_col;
183 /* Rows of zeroes can be exploited in the same way as we did with columns.
184 * However, the column calculation has created many nonzero AC terms, so
185 * the simplification applies less often (typically 5% to 10% of the time).
186 * And testing floats for zero is relatively expensive, so we don't bother.
187 */
188
189 /* Even part */
190
191 /* Prepare range-limit and float->int conversion */
192 z5 = wsptr[0] + (((FAST_FLOAT) RANGE_CENTER) + ((FAST_FLOAT) 0.5));
193 tmp10 = z5 + wsptr[4];
194 tmp11 = z5 - wsptr[4];
195
196 tmp13 = wsptr[2] + wsptr[6];
197 tmp12 = (wsptr[2] - wsptr[6]) *
198 ((FAST_FLOAT) 1.414213562) - tmp13; /* 2*c4 */
199
200 tmp0 = tmp10 + tmp13;
201 tmp3 = tmp10 - tmp13;
202 tmp1 = tmp11 + tmp12;
203 tmp2 = tmp11 - tmp12;
204
205 /* Odd part */
206
207 z13 = wsptr[5] + wsptr[3];
208 z10 = wsptr[5] - wsptr[3];
209 z11 = wsptr[1] + wsptr[7];
210 z12 = wsptr[1] - wsptr[7];
211
212 tmp7 = z11 + z13; /* phase 5 */
213 tmp11 = (z11 - z13) * ((FAST_FLOAT) 1.414213562); /* 2*c4 */
214
215 z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2*c2 */
216 tmp10 = z5 - z12 * ((FAST_FLOAT) 1.082392200); /* 2*(c2-c6) */
217 tmp12 = z5 - z10 * ((FAST_FLOAT) 2.613125930); /* 2*(c2+c6) */
218
219 tmp6 = tmp12 - tmp7; /* phase 2 */
220 tmp5 = tmp11 - tmp6;
221 tmp4 = tmp10 - tmp5;
222
223 /* Final output stage: float->int conversion and range-limit */
224
225 outptr[0] = range_limit[(int) (tmp0 + tmp7) & RANGE_MASK];
226 outptr[7] = range_limit[(int) (tmp0 - tmp7) & RANGE_MASK];
227 outptr[1] = range_limit[(int) (tmp1 + tmp6) & RANGE_MASK];
228 outptr[6] = range_limit[(int) (tmp1 - tmp6) & RANGE_MASK];
229 outptr[2] = range_limit[(int) (tmp2 + tmp5) & RANGE_MASK];
230 outptr[5] = range_limit[(int) (tmp2 - tmp5) & RANGE_MASK];
231 outptr[3] = range_limit[(int) (tmp3 + tmp4) & RANGE_MASK];
232 outptr[4] = range_limit[(int) (tmp3 - tmp4) & RANGE_MASK];
233
234 wsptr += DCTSIZE; /* advance pointer to next row */
235 }
236 }
237
238 #endif /* DCT_FLOAT_SUPPORTED */
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