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| 1 /* | |
| 2 * jidctfst.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 fast, not so accurate integer 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 * A 2-D IDCT can be done by 1-D IDCT on each column followed by 1-D IDCT | |
| 13 * on each row (or vice versa, but it's more convenient to emit a row at | |
| 14 * a time). Direct algorithms are also available, but they are much more | |
| 15 * complex and seem not to be any faster when reduced to code. | |
| 16 * | |
| 17 * This implementation is based on Arai, Agui, and Nakajima's algorithm for | |
| 18 * scaled DCT. Their original paper (Trans. IEICE E-71(11):1095) is in | |
| 19 * Japanese, but the algorithm is described in the Pennebaker & Mitchell | |
| 20 * JPEG textbook (see REFERENCES section in file README). The following code | |
| 21 * is based directly on figure 4-8 in P&M. | |
| 22 * While an 8-point DCT cannot be done in less than 11 multiplies, it is | |
| 23 * possible to arrange the computation so that many of the multiplies are | |
| 24 * simple scalings of the final outputs. These multiplies can then be | |
| 25 * folded into the multiplications or divisions by the JPEG quantization | |
| 26 * table entries. The AA&N method leaves only 5 multiplies and 29 adds | |
| 27 * to be done in the DCT itself. | |
| 28 * The primary disadvantage of this method is that with fixed-point math, | |
| 29 * accuracy is lost due to imprecise representation of the scaled | |
| 30 * quantization values. The smaller the quantization table entry, the less | |
| 31 * precise the scaled value, so this implementation does worse with high- | |
| 32 * quality-setting files than with low-quality ones. | |
| 33 */ | |
| 34 | |
| 35 #define JPEG_INTERNALS | |
| 36 #include "jinclude.h" | |
| 37 #include "jpeglib.h" | |
| 38 #include "jdct.h" /* Private declarations for DCT subsystem */ | |
| 39 | |
| 40 #ifdef DCT_IFAST_SUPPORTED | |
| 41 | |
| 42 | |
| 43 /* | |
| 44 * This module is specialized to the case DCTSIZE = 8. | |
| 45 */ | |
| 46 | |
| 47 #if DCTSIZE != 8 | |
| 48 Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */ | |
| 49 #endif | |
| 50 | |
| 51 | |
| 52 /* Scaling decisions are generally the same as in the LL&M algorithm; | |
| 53 * see jidctint.c for more details. However, we choose to descale | |
| 54 * (right shift) multiplication products as soon as they are formed, | |
| 55 * rather than carrying additional fractional bits into subsequent additions. | |
| 56 * This compromises accuracy slightly, but it lets us save a few shifts. | |
| 57 * More importantly, 16-bit arithmetic is then adequate (for 8-bit samples) | |
| 58 * everywhere except in the multiplications proper; this saves a good deal | |
| 59 * of work on 16-bit-int machines. | |
| 60 * | |
| 61 * The dequantized coefficients are not integers because the AA&N scaling | |
| 62 * factors have been incorporated. We represent them scaled up by PASS1_BITS, | |
| 63 * so that the first and second IDCT rounds have the same input scaling. | |
| 64 * For 8-bit JSAMPLEs, we choose IFAST_SCALE_BITS = PASS1_BITS so as to | |
| 65 * avoid a descaling shift; this compromises accuracy rather drastically | |
| 66 * for small quantization table entries, but it saves a lot of shifts. | |
| 67 * For 12-bit JSAMPLEs, there's no hope of using 16x16 multiplies anyway, | |
| 68 * so we use a much larger scaling factor to preserve accuracy. | |
| 69 * | |
| 70 * A final compromise is to represent the multiplicative constants to only | |
| 71 * 8 fractional bits, rather than 13. This saves some shifting work on some | |
| 72 * machines, and may also reduce the cost of multiplication (since there | |
| 73 * are fewer one-bits in the constants). | |
| 74 */ | |
| 75 | |
| 76 #if BITS_IN_JSAMPLE == 8 | |
| 77 #define CONST_BITS 8 | |
| 78 #define PASS1_BITS 2 | |
| 79 #else | |
| 80 #define CONST_BITS 8 | |
| 81 #define PASS1_BITS 1 /* lose a little precision to avoid overflow */ | |
| 82 #endif | |
| 83 | |
| 84 /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus | |
| 85 * causing a lot of useless floating-point operations at run time. | |
| 86 * To get around this we use the following pre-calculated constants. | |
| 87 * If you change CONST_BITS you may want to add appropriate values. | |
| 88 * (With a reasonable C compiler, you can just rely on the FIX() macro...) | |
| 89 */ | |
| 90 | |
| 91 #if CONST_BITS == 8 | |
| 92 #define FIX_1_082392200 ((INT32) 277) /* FIX(1.082392200) */ | |
| 93 #define FIX_1_414213562 ((INT32) 362) /* FIX(1.414213562) */ | |
| 94 #define FIX_1_847759065 ((INT32) 473) /* FIX(1.847759065) */ | |
| 95 #define FIX_2_613125930 ((INT32) 669) /* FIX(2.613125930) */ | |
| 96 #else | |
| 97 #define FIX_1_082392200 FIX(1.082392200) | |
| 98 #define FIX_1_414213562 FIX(1.414213562) | |
| 99 #define FIX_1_847759065 FIX(1.847759065) | |
| 100 #define FIX_2_613125930 FIX(2.613125930) | |
| 101 #endif | |
| 102 | |
| 103 | |
| 104 /* We can gain a little more speed, with a further compromise in accuracy, | |
| 105 * by omitting the addition in a descaling shift. This yields an incorrectly | |
| 106 * rounded result half the time... | |
| 107 */ | |
| 108 | |
| 109 #ifndef USE_ACCURATE_ROUNDING | |
| 110 #undef DESCALE | |
| 111 #define DESCALE(x,n) RIGHT_SHIFT(x, n) | |
| 112 #endif | |
| 113 | |
| 114 | |
| 115 /* Multiply a DCTELEM variable by an INT32 constant, and immediately | |
| 116 * descale to yield a DCTELEM result. | |
| 117 */ | |
| 118 | |
| 119 #define MULTIPLY(var,const) ((DCTELEM) DESCALE((var) * (const), CONST_BITS)) | |
| 120 | |
| 121 | |
| 122 /* Dequantize a coefficient by multiplying it by the multiplier-table | |
| 123 * entry; produce a DCTELEM result. For 8-bit data a 16x16->16 | |
| 124 * multiplication will do. For 12-bit data, the multiplier table is | |
| 125 * declared INT32, so a 32-bit multiply will be used. | |
| 126 */ | |
| 127 | |
| 128 #if BITS_IN_JSAMPLE == 8 | |
| 129 #define DEQUANTIZE(coef,quantval) (((IFAST_MULT_TYPE) (coef)) * (quantval)) | |
| 130 #else | |
| 131 #define DEQUANTIZE(coef,quantval) \ | |
| 132 DESCALE((coef)*(quantval), IFAST_SCALE_BITS-PASS1_BITS) | |
| 133 #endif | |
| 134 | |
| 135 | |
| 136 /* Like DESCALE, but applies to a DCTELEM and produces an int. | |
| 137 * We assume that int right shift is unsigned if INT32 right shift is. | |
| 138 */ | |
| 139 | |
| 140 #ifdef RIGHT_SHIFT_IS_UNSIGNED | |
| 141 #define ISHIFT_TEMPS DCTELEM ishift_temp; | |
| 142 #if BITS_IN_JSAMPLE == 8 | |
| 143 #define DCTELEMBITS 16 /* DCTELEM may be 16 or 32 bits */ | |
| 144 #else | |
| 145 #define DCTELEMBITS 32 /* DCTELEM must be 32 bits */ | |
| 146 #endif | |
| 147 #define IRIGHT_SHIFT(x,shft) \ | |
| 148 ((ishift_temp = (x)) < 0 ? \ | |
| 149 (ishift_temp >> (shft)) | ((~((DCTELEM) 0)) << (DCTELEMBITS-(shft))) : \ | |
| 150 (ishift_temp >> (shft))) | |
| 151 #else | |
| 152 #define ISHIFT_TEMPS | |
| 153 #define IRIGHT_SHIFT(x,shft) ((x) >> (shft)) | |
| 154 #endif | |
| 155 | |
| 156 #ifdef USE_ACCURATE_ROUNDING | |
| 157 #define IDESCALE(x,n) ((int) IRIGHT_SHIFT((x) + (1 << ((n)-1)), n)) | |
| 158 #else | |
| 159 #define IDESCALE(x,n) ((int) IRIGHT_SHIFT(x, n)) | |
| 160 #endif | |
| 161 | |
| 162 | |
| 163 /* | |
| 164 * Perform dequantization and inverse DCT on one block of coefficients. | |
| 165 */ | |
| 166 | |
| 167 GLOBAL(void) | |
| 168 jpeg_idct_ifast (j_decompress_ptr cinfo, jpeg_component_info * compptr, | |
| 169 JCOEFPTR coef_block, | |
| 170 JSAMPARRAY output_buf, JDIMENSION output_col) | |
| 171 { | |
| 172 DCTELEM tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7; | |
| 173 DCTELEM tmp10, tmp11, tmp12, tmp13; | |
| 174 DCTELEM z5, z10, z11, z12, z13; | |
| 175 JCOEFPTR inptr; | |
| 176 IFAST_MULT_TYPE * quantptr; | |
| 177 int * wsptr; | |
| 178 JSAMPROW outptr; | |
| 179 JSAMPLE *range_limit = IDCT_range_limit(cinfo); | |
| 180 int ctr; | |
| 181 int workspace[DCTSIZE2]; /* buffers data between passes */ | |
| 182 SHIFT_TEMPS /* for DESCALE */ | |
| 183 ISHIFT_TEMPS /* for IDESCALE */ | |
| 184 | |
| 185 /* Pass 1: process columns from input, store into work array. */ | |
| 186 | |
| 187 inptr = coef_block; | |
| 188 quantptr = (IFAST_MULT_TYPE *) compptr->dct_table; | |
| 189 wsptr = workspace; | |
| 190 for (ctr = DCTSIZE; ctr > 0; ctr--) { | |
| 191 /* Due to quantization, we will usually find that many of the input | |
| 192 * coefficients are zero, especially the AC terms. We can exploit this | |
| 193 * by short-circuiting the IDCT calculation for any column in which all | |
| 194 * the AC terms are zero. In that case each output is equal to the | |
| 195 * DC coefficient (with scale factor as needed). | |
| 196 * With typical images and quantization tables, half or more of the | |
| 197 * column DCT calculations can be simplified this way. | |
| 198 */ | |
| 199 | |
| 200 if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 && | |
| 201 inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*4] == 0 && | |
| 202 inptr[DCTSIZE*5] == 0 && inptr[DCTSIZE*6] == 0 && | |
| 203 inptr[DCTSIZE*7] == 0) { | |
| 204 /* AC terms all zero */ | |
| 205 int dcval = (int) DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]); | |
| 206 | |
| 207 wsptr[DCTSIZE*0] = dcval; | |
| 208 wsptr[DCTSIZE*1] = dcval; | |
| 209 wsptr[DCTSIZE*2] = dcval; | |
| 210 wsptr[DCTSIZE*3] = dcval; | |
| 211 wsptr[DCTSIZE*4] = dcval; | |
| 212 wsptr[DCTSIZE*5] = dcval; | |
| 213 wsptr[DCTSIZE*6] = dcval; | |
| 214 wsptr[DCTSIZE*7] = dcval; | |
| 215 | |
| 216 inptr++; /* advance pointers to next column */ | |
| 217 quantptr++; | |
| 218 wsptr++; | |
| 219 continue; | |
| 220 } | |
| 221 | |
| 222 /* Even part */ | |
| 223 | |
| 224 tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]); | |
| 225 tmp1 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]); | |
| 226 tmp2 = DEQUANTIZE(inptr[DCTSIZE*4], quantptr[DCTSIZE*4]); | |
| 227 tmp3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]); | |
| 228 | |
| 229 tmp10 = tmp0 + tmp2; /* phase 3 */ | |
| 230 tmp11 = tmp0 - tmp2; | |
| 231 | |
| 232 tmp13 = tmp1 + tmp3; /* phases 5-3 */ | |
| 233 tmp12 = MULTIPLY(tmp1 - tmp3, FIX_1_414213562) - tmp13; /* 2*c4 */ | |
| 234 | |
| 235 tmp0 = tmp10 + tmp13; /* phase 2 */ | |
| 236 tmp3 = tmp10 - tmp13; | |
| 237 tmp1 = tmp11 + tmp12; | |
| 238 tmp2 = tmp11 - tmp12; | |
| 239 | |
| 240 /* Odd part */ | |
| 241 | |
| 242 tmp4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]); | |
| 243 tmp5 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]); | |
| 244 tmp6 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]); | |
| 245 tmp7 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]); | |
| 246 | |
| 247 z13 = tmp6 + tmp5; /* phase 6 */ | |
| 248 z10 = tmp6 - tmp5; | |
| 249 z11 = tmp4 + tmp7; | |
| 250 z12 = tmp4 - tmp7; | |
| 251 | |
| 252 tmp7 = z11 + z13; /* phase 5 */ | |
| 253 tmp11 = MULTIPLY(z11 - z13, FIX_1_414213562); /* 2*c4 */ | |
| 254 | |
| 255 z5 = MULTIPLY(z10 + z12, FIX_1_847759065); /* 2*c2 */ | |
| 256 tmp10 = MULTIPLY(z12, FIX_1_082392200) - z5; /* 2*(c2-c6) */ | |
| 257 tmp12 = MULTIPLY(z10, - FIX_2_613125930) + z5; /* -2*(c2+c6) */ | |
| 258 | |
| 259 tmp6 = tmp12 - tmp7; /* phase 2 */ | |
| 260 tmp5 = tmp11 - tmp6; | |
| 261 tmp4 = tmp10 + tmp5; | |
| 262 | |
| 263 wsptr[DCTSIZE*0] = (int) (tmp0 + tmp7); | |
| 264 wsptr[DCTSIZE*7] = (int) (tmp0 - tmp7); | |
| 265 wsptr[DCTSIZE*1] = (int) (tmp1 + tmp6); | |
| 266 wsptr[DCTSIZE*6] = (int) (tmp1 - tmp6); | |
| 267 wsptr[DCTSIZE*2] = (int) (tmp2 + tmp5); | |
| 268 wsptr[DCTSIZE*5] = (int) (tmp2 - tmp5); | |
| 269 wsptr[DCTSIZE*4] = (int) (tmp3 + tmp4); | |
| 270 wsptr[DCTSIZE*3] = (int) (tmp3 - tmp4); | |
| 271 | |
| 272 inptr++; /* advance pointers to next column */ | |
| 273 quantptr++; | |
| 274 wsptr++; | |
| 275 } | |
| 276 | |
| 277 /* Pass 2: process rows from work array, store into output array. */ | |
| 278 /* Note that we must descale the results by a factor of 8 == 2**3, */ | |
| 279 /* and also undo the PASS1_BITS scaling. */ | |
| 280 | |
| 281 wsptr = workspace; | |
| 282 for (ctr = 0; ctr < DCTSIZE; ctr++) { | |
| 283 outptr = output_buf[ctr] + output_col; | |
| 284 /* Rows of zeroes can be exploited in the same way as we did with columns. | |
| 285 * However, the column calculation has created many nonzero AC terms, so | |
| 286 * the simplification applies less often (typically 5% to 10% of the time). | |
| 287 * On machines with very fast multiplication, it's possible that the | |
| 288 * test takes more time than it's worth. In that case this section | |
| 289 * may be commented out. | |
| 290 */ | |
| 291 | |
| 292 #ifndef NO_ZERO_ROW_TEST | |
| 293 if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 && wsptr[4] == 0 && | |
| 294 wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) { | |
| 295 /* AC terms all zero */ | |
| 296 JSAMPLE dcval = range_limit[IDESCALE(wsptr[0], PASS1_BITS+3) | |
| 297 & RANGE_MASK]; | |
| 298 | |
| 299 outptr[0] = dcval; | |
| 300 outptr[1] = dcval; | |
| 301 outptr[2] = dcval; | |
| 302 outptr[3] = dcval; | |
| 303 outptr[4] = dcval; | |
| 304 outptr[5] = dcval; | |
| 305 outptr[6] = dcval; | |
| 306 outptr[7] = dcval; | |
| 307 | |
| 308 wsptr += DCTSIZE; /* advance pointer to next row */ | |
| 309 continue; | |
| 310 } | |
| 311 #endif | |
| 312 | |
| 313 /* Even part */ | |
| 314 | |
| 315 tmp10 = ((DCTELEM) wsptr[0] + (DCTELEM) wsptr[4]); | |
| 316 tmp11 = ((DCTELEM) wsptr[0] - (DCTELEM) wsptr[4]); | |
| 317 | |
| 318 tmp13 = ((DCTELEM) wsptr[2] + (DCTELEM) wsptr[6]); | |
| 319 tmp12 = MULTIPLY((DCTELEM) wsptr[2] - (DCTELEM) wsptr[6], FIX_1_414213562) | |
| 320 - tmp13; | |
| 321 | |
| 322 tmp0 = tmp10 + tmp13; | |
| 323 tmp3 = tmp10 - tmp13; | |
| 324 tmp1 = tmp11 + tmp12; | |
| 325 tmp2 = tmp11 - tmp12; | |
| 326 | |
| 327 /* Odd part */ | |
| 328 | |
| 329 z13 = (DCTELEM) wsptr[5] + (DCTELEM) wsptr[3]; | |
| 330 z10 = (DCTELEM) wsptr[5] - (DCTELEM) wsptr[3]; | |
| 331 z11 = (DCTELEM) wsptr[1] + (DCTELEM) wsptr[7]; | |
| 332 z12 = (DCTELEM) wsptr[1] - (DCTELEM) wsptr[7]; | |
| 333 | |
| 334 tmp7 = z11 + z13; /* phase 5 */ | |
| 335 tmp11 = MULTIPLY(z11 - z13, FIX_1_414213562); /* 2*c4 */ | |
| 336 | |
| 337 z5 = MULTIPLY(z10 + z12, FIX_1_847759065); /* 2*c2 */ | |
| 338 tmp10 = MULTIPLY(z12, FIX_1_082392200) - z5; /* 2*(c2-c6) */ | |
| 339 tmp12 = MULTIPLY(z10, - FIX_2_613125930) + z5; /* -2*(c2+c6) */ | |
| 340 | |
| 341 tmp6 = tmp12 - tmp7; /* phase 2 */ | |
| 342 tmp5 = tmp11 - tmp6; | |
| 343 tmp4 = tmp10 + tmp5; | |
| 344 | |
| 345 /* Final output stage: scale down by a factor of 8 and range-limit */ | |
| 346 | |
| 347 outptr[0] = range_limit[IDESCALE(tmp0 + tmp7, PASS1_BITS+3) | |
| 348 & RANGE_MASK]; | |
| 349 outptr[7] = range_limit[IDESCALE(tmp0 - tmp7, PASS1_BITS+3) | |
| 350 & RANGE_MASK]; | |
| 351 outptr[1] = range_limit[IDESCALE(tmp1 + tmp6, PASS1_BITS+3) | |
| 352 & RANGE_MASK]; | |
| 353 outptr[6] = range_limit[IDESCALE(tmp1 - tmp6, PASS1_BITS+3) | |
| 354 & RANGE_MASK]; | |
| 355 outptr[2] = range_limit[IDESCALE(tmp2 + tmp5, PASS1_BITS+3) | |
| 356 & RANGE_MASK]; | |
| 357 outptr[5] = range_limit[IDESCALE(tmp2 - tmp5, PASS1_BITS+3) | |
| 358 & RANGE_MASK]; | |
| 359 outptr[4] = range_limit[IDESCALE(tmp3 + tmp4, PASS1_BITS+3) | |
| 360 & RANGE_MASK]; | |
| 361 outptr[3] = range_limit[IDESCALE(tmp3 - tmp4, PASS1_BITS+3) | |
| 362 & RANGE_MASK]; | |
| 363 | |
| 364 wsptr += DCTSIZE; /* advance pointer to next row */ | |
| 365 } | |
| 366 } | |
| 367 | |
| 368 #endif /* DCT_IFAST_SUPPORTED */ | |
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Chromium Code Reviews
Issue 1705523002:
Remove libjpeg and libjpeg_turbo. (Closed)
Base URL: https://github.com/domokit/mojo.git@master