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| 1 /* | |
| 2 * jidctint.c | |
| 3 * | |
| 4 * Copyright (C) 1991-1998, 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 slow-but-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 an algorithm described in | |
| 18 * C. Loeffler, A. Ligtenberg and G. Moschytz, "Practical Fast 1-D DCT | |
| 19 * Algorithms with 11 Multiplications", Proc. Int'l. Conf. on Acoustics, | |
| 20 * Speech, and Signal Processing 1989 (ICASSP '89), pp. 988-991. | |
| 21 * The primary algorithm described there uses 11 multiplies and 29 adds. | |
| 22 * We use their alternate method with 12 multiplies and 32 adds. | |
| 23 * The advantage of this method is that no data path contains more than one | |
| 24 * multiplication; this allows a very simple and accurate implementation in | |
| 25 * scaled fixed-point arithmetic, with a minimal number of shifts. | |
| 26 */ | |
| 27 | |
| 28 #define JPEG_INTERNALS | |
| 29 #include "jinclude.h" | |
| 30 #include "jpeglib.h" | |
| 31 #include "jdct.h" /* Private declarations for DCT subsystem */ | |
| 32 | |
| 33 #ifdef DCT_ISLOW_SUPPORTED | |
| 34 | |
| 35 | |
| 36 /* | |
| 37 * This module is specialized to the case DCTSIZE = 8. | |
| 38 */ | |
| 39 | |
| 40 #if DCTSIZE != 8 | |
| 41 Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */ | |
| 42 #endif | |
| 43 | |
| 44 | |
| 45 /* | |
| 46 * The poop on this scaling stuff is as follows: | |
| 47 * | |
| 48 * Each 1-D IDCT step produces outputs which are a factor of sqrt(N) | |
| 49 * larger than the true IDCT outputs. The final outputs are therefore | |
| 50 * a factor of N larger than desired; since N=8 this can be cured by | |
| 51 * a simple right shift at the end of the algorithm. The advantage of | |
| 52 * this arrangement is that we save two multiplications per 1-D IDCT, | |
| 53 * because the y0 and y4 inputs need not be divided by sqrt(N). | |
| 54 * | |
| 55 * We have to do addition and subtraction of the integer inputs, which | |
| 56 * is no problem, and multiplication by fractional constants, which is | |
| 57 * a problem to do in integer arithmetic. We multiply all the constants | |
| 58 * by CONST_SCALE and convert them to integer constants (thus retaining | |
| 59 * CONST_BITS bits of precision in the constants). After doing a | |
| 60 * multiplication we have to divide the product by CONST_SCALE, with proper | |
| 61 * rounding, to produce the correct output. This division can be done | |
| 62 * cheaply as a right shift of CONST_BITS bits. We postpone shifting | |
| 63 * as long as possible so that partial sums can be added together with | |
| 64 * full fractional precision. | |
| 65 * | |
| 66 * The outputs of the first pass are scaled up by PASS1_BITS bits so that | |
| 67 * they are represented to better-than-integral precision. These outputs | |
| 68 * require BITS_IN_JSAMPLE + PASS1_BITS + 3 bits; this fits in a 16-bit word | |
| 69 * with the recommended scaling. (To scale up 12-bit sample data further, an | |
| 70 * intermediate INT32 array would be needed.) | |
| 71 * | |
| 72 * To avoid overflow of the 32-bit intermediate results in pass 2, we must | |
| 73 * have BITS_IN_JSAMPLE + CONST_BITS + PASS1_BITS <= 26. Error analysis | |
| 74 * shows that the values given below are the most effective. | |
| 75 */ | |
| 76 | |
| 77 #if BITS_IN_JSAMPLE == 8 | |
| 78 #define CONST_BITS 13 | |
| 79 #define PASS1_BITS 2 | |
| 80 #else | |
| 81 #define CONST_BITS 13 | |
| 82 #define PASS1_BITS 1 /* lose a little precision to avoid overflow */ | |
| 83 #endif | |
| 84 | |
| 85 /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus | |
| 86 * causing a lot of useless floating-point operations at run time. | |
| 87 * To get around this we use the following pre-calculated constants. | |
| 88 * If you change CONST_BITS you may want to add appropriate values. | |
| 89 * (With a reasonable C compiler, you can just rely on the FIX() macro...) | |
| 90 */ | |
| 91 | |
| 92 #if CONST_BITS == 13 | |
| 93 #define FIX_0_298631336 ((INT32) 2446) /* FIX(0.298631336) */ | |
| 94 #define FIX_0_390180644 ((INT32) 3196) /* FIX(0.390180644) */ | |
| 95 #define FIX_0_541196100 ((INT32) 4433) /* FIX(0.541196100) */ | |
| 96 #define FIX_0_765366865 ((INT32) 6270) /* FIX(0.765366865) */ | |
| 97 #define FIX_0_899976223 ((INT32) 7373) /* FIX(0.899976223) */ | |
| 98 #define FIX_1_175875602 ((INT32) 9633) /* FIX(1.175875602) */ | |
| 99 #define FIX_1_501321110 ((INT32) 12299) /* FIX(1.501321110) */ | |
| 100 #define FIX_1_847759065 ((INT32) 15137) /* FIX(1.847759065) */ | |
| 101 #define FIX_1_961570560 ((INT32) 16069) /* FIX(1.961570560) */ | |
| 102 #define FIX_2_053119869 ((INT32) 16819) /* FIX(2.053119869) */ | |
| 103 #define FIX_2_562915447 ((INT32) 20995) /* FIX(2.562915447) */ | |
| 104 #define FIX_3_072711026 ((INT32) 25172) /* FIX(3.072711026) */ | |
| 105 #else | |
| 106 #define FIX_0_298631336 FIX(0.298631336) | |
| 107 #define FIX_0_390180644 FIX(0.390180644) | |
| 108 #define FIX_0_541196100 FIX(0.541196100) | |
| 109 #define FIX_0_765366865 FIX(0.765366865) | |
| 110 #define FIX_0_899976223 FIX(0.899976223) | |
| 111 #define FIX_1_175875602 FIX(1.175875602) | |
| 112 #define FIX_1_501321110 FIX(1.501321110) | |
| 113 #define FIX_1_847759065 FIX(1.847759065) | |
| 114 #define FIX_1_961570560 FIX(1.961570560) | |
| 115 #define FIX_2_053119869 FIX(2.053119869) | |
| 116 #define FIX_2_562915447 FIX(2.562915447) | |
| 117 #define FIX_3_072711026 FIX(3.072711026) | |
| 118 #endif | |
| 119 | |
| 120 | |
| 121 /* Multiply an INT32 variable by an INT32 constant to yield an INT32 result. | |
| 122 * For 8-bit samples with the recommended scaling, all the variable | |
| 123 * and constant values involved are no more than 16 bits wide, so a | |
| 124 * 16x16->32 bit multiply can be used instead of a full 32x32 multiply. | |
| 125 * For 12-bit samples, a full 32-bit multiplication will be needed. | |
| 126 */ | |
| 127 | |
| 128 #if BITS_IN_JSAMPLE == 8 | |
| 129 #define MULTIPLY(var,const) MULTIPLY16C16(var,const) | |
| 130 #else | |
| 131 #define MULTIPLY(var,const) ((var) * (const)) | |
| 132 #endif | |
| 133 | |
| 134 | |
| 135 /* Dequantize a coefficient by multiplying it by the multiplier-table | |
| 136 * entry; produce an int result. In this module, both inputs and result | |
| 137 * are 16 bits or less, so either int or short multiply will work. | |
| 138 */ | |
| 139 | |
| 140 #define DEQUANTIZE(coef,quantval) (((ISLOW_MULT_TYPE) (coef)) * (quantval)) | |
| 141 | |
| 142 | |
| 143 /* | |
| 144 * Perform dequantization and inverse DCT on one block of coefficients. | |
| 145 */ | |
| 146 | |
| 147 GLOBAL(void) | |
| 148 jpeg_idct_islow (j_decompress_ptr cinfo, jpeg_component_info * compptr, | |
| 149 JCOEFPTR coef_block, | |
| 150 JSAMPARRAY output_buf, JDIMENSION output_col) | |
| 151 { | |
| 152 INT32 tmp0, tmp1, tmp2, tmp3; | |
| 153 INT32 tmp10, tmp11, tmp12, tmp13; | |
| 154 INT32 z1, z2, z3, z4, z5; | |
| 155 JCOEFPTR inptr; | |
| 156 ISLOW_MULT_TYPE * quantptr; | |
| 157 int * wsptr; | |
| 158 JSAMPROW outptr; | |
| 159 JSAMPLE *range_limit = IDCT_range_limit(cinfo); | |
| 160 int ctr; | |
| 161 int workspace[DCTSIZE2]; /* buffers data between passes */ | |
| 162 SHIFT_TEMPS | |
| 163 | |
| 164 /* Pass 1: process columns from input, store into work array. */ | |
| 165 /* Note results are scaled up by sqrt(8) compared to a true IDCT; */ | |
| 166 /* furthermore, we scale the results by 2**PASS1_BITS. */ | |
| 167 | |
| 168 inptr = coef_block; | |
| 169 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table; | |
| 170 wsptr = workspace; | |
| 171 for (ctr = DCTSIZE; ctr > 0; ctr--) { | |
| 172 /* Due to quantization, we will usually find that many of the input | |
| 173 * coefficients are zero, especially the AC terms. We can exploit this | |
| 174 * by short-circuiting the IDCT calculation for any column in which all | |
| 175 * the AC terms are zero. In that case each output is equal to the | |
| 176 * DC coefficient (with scale factor as needed). | |
| 177 * With typical images and quantization tables, half or more of the | |
| 178 * column DCT calculations can be simplified this way. | |
| 179 */ | |
| 180 | |
| 181 if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 && | |
| 182 inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*4] == 0 && | |
| 183 inptr[DCTSIZE*5] == 0 && inptr[DCTSIZE*6] == 0 && | |
| 184 inptr[DCTSIZE*7] == 0) { | |
| 185 /* AC terms all zero */ | |
| 186 int dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << PASS1_BIT
S; | |
| 187 | |
| 188 wsptr[DCTSIZE*0] = dcval; | |
| 189 wsptr[DCTSIZE*1] = dcval; | |
| 190 wsptr[DCTSIZE*2] = dcval; | |
| 191 wsptr[DCTSIZE*3] = dcval; | |
| 192 wsptr[DCTSIZE*4] = dcval; | |
| 193 wsptr[DCTSIZE*5] = dcval; | |
| 194 wsptr[DCTSIZE*6] = dcval; | |
| 195 wsptr[DCTSIZE*7] = dcval; | |
| 196 | |
| 197 inptr++; /* advance pointers to next column */ | |
| 198 quantptr++; | |
| 199 wsptr++; | |
| 200 continue; | |
| 201 } | |
| 202 | |
| 203 /* Even part: reverse the even part of the forward DCT. */ | |
| 204 /* The rotator is sqrt(2)*c(-6). */ | |
| 205 | |
| 206 z2 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]); | |
| 207 z3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]); | |
| 208 | |
| 209 z1 = MULTIPLY(z2 + z3, FIX_0_541196100); | |
| 210 tmp2 = z1 + MULTIPLY(z3, - FIX_1_847759065); | |
| 211 tmp3 = z1 + MULTIPLY(z2, FIX_0_765366865); | |
| 212 | |
| 213 z2 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]); | |
| 214 z3 = DEQUANTIZE(inptr[DCTSIZE*4], quantptr[DCTSIZE*4]); | |
| 215 | |
| 216 tmp0 = (z2 + z3) << CONST_BITS; | |
| 217 tmp1 = (z2 - z3) << CONST_BITS; | |
| 218 | |
| 219 tmp10 = tmp0 + tmp3; | |
| 220 tmp13 = tmp0 - tmp3; | |
| 221 tmp11 = tmp1 + tmp2; | |
| 222 tmp12 = tmp1 - tmp2; | |
| 223 | |
| 224 /* Odd part per figure 8; the matrix is unitary and hence its | |
| 225 * transpose is its inverse. i0..i3 are y7,y5,y3,y1 respectively. | |
| 226 */ | |
| 227 | |
| 228 tmp0 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]); | |
| 229 tmp1 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]); | |
| 230 tmp2 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]); | |
| 231 tmp3 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]); | |
| 232 | |
| 233 z1 = tmp0 + tmp3; | |
| 234 z2 = tmp1 + tmp2; | |
| 235 z3 = tmp0 + tmp2; | |
| 236 z4 = tmp1 + tmp3; | |
| 237 z5 = MULTIPLY(z3 + z4, FIX_1_175875602); /* sqrt(2) * c3 */ | |
| 238 | |
| 239 tmp0 = MULTIPLY(tmp0, FIX_0_298631336); /* sqrt(2) * (-c1+c3+c5-c7) */ | |
| 240 tmp1 = MULTIPLY(tmp1, FIX_2_053119869); /* sqrt(2) * ( c1+c3-c5+c7) */ | |
| 241 tmp2 = MULTIPLY(tmp2, FIX_3_072711026); /* sqrt(2) * ( c1+c3+c5-c7) */ | |
| 242 tmp3 = MULTIPLY(tmp3, FIX_1_501321110); /* sqrt(2) * ( c1+c3-c5-c7) */ | |
| 243 z1 = MULTIPLY(z1, - FIX_0_899976223); /* sqrt(2) * (c7-c3) */ | |
| 244 z2 = MULTIPLY(z2, - FIX_2_562915447); /* sqrt(2) * (-c1-c3) */ | |
| 245 z3 = MULTIPLY(z3, - FIX_1_961570560); /* sqrt(2) * (-c3-c5) */ | |
| 246 z4 = MULTIPLY(z4, - FIX_0_390180644); /* sqrt(2) * (c5-c3) */ | |
| 247 | |
| 248 z3 += z5; | |
| 249 z4 += z5; | |
| 250 | |
| 251 tmp0 += z1 + z3; | |
| 252 tmp1 += z2 + z4; | |
| 253 tmp2 += z2 + z3; | |
| 254 tmp3 += z1 + z4; | |
| 255 | |
| 256 /* Final output stage: inputs are tmp10..tmp13, tmp0..tmp3 */ | |
| 257 | |
| 258 wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp3, CONST_BITS-PASS1_BITS); | |
| 259 wsptr[DCTSIZE*7] = (int) DESCALE(tmp10 - tmp3, CONST_BITS-PASS1_BITS); | |
| 260 wsptr[DCTSIZE*1] = (int) DESCALE(tmp11 + tmp2, CONST_BITS-PASS1_BITS); | |
| 261 wsptr[DCTSIZE*6] = (int) DESCALE(tmp11 - tmp2, CONST_BITS-PASS1_BITS); | |
| 262 wsptr[DCTSIZE*2] = (int) DESCALE(tmp12 + tmp1, CONST_BITS-PASS1_BITS); | |
| 263 wsptr[DCTSIZE*5] = (int) DESCALE(tmp12 - tmp1, CONST_BITS-PASS1_BITS); | |
| 264 wsptr[DCTSIZE*3] = (int) DESCALE(tmp13 + tmp0, CONST_BITS-PASS1_BITS); | |
| 265 wsptr[DCTSIZE*4] = (int) DESCALE(tmp13 - tmp0, CONST_BITS-PASS1_BITS); | |
| 266 | |
| 267 inptr++; /* advance pointers to next column */ | |
| 268 quantptr++; | |
| 269 wsptr++; | |
| 270 } | |
| 271 | |
| 272 /* Pass 2: process rows from work array, store into output array. */ | |
| 273 /* Note that we must descale the results by a factor of 8 == 2**3, */ | |
| 274 /* and also undo the PASS1_BITS scaling. */ | |
| 275 | |
| 276 wsptr = workspace; | |
| 277 for (ctr = 0; ctr < DCTSIZE; ctr++) { | |
| 278 outptr = output_buf[ctr] + output_col; | |
| 279 /* Rows of zeroes can be exploited in the same way as we did with columns. | |
| 280 * However, the column calculation has created many nonzero AC terms, so | |
| 281 * the simplification applies less often (typically 5% to 10% of the time). | |
| 282 * On machines with very fast multiplication, it's possible that the | |
| 283 * test takes more time than it's worth. In that case this section | |
| 284 * may be commented out. | |
| 285 */ | |
| 286 | |
| 287 #ifndef NO_ZERO_ROW_TEST | |
| 288 if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 && wsptr[4] == 0 && | |
| 289 wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) { | |
| 290 /* AC terms all zero */ | |
| 291 JSAMPLE dcval = range_limit[(int) DESCALE((INT32) wsptr[0], PASS1_BITS+3) | |
| 292 & RANGE_MASK]; | |
| 293 | |
| 294 outptr[0] = dcval; | |
| 295 outptr[1] = dcval; | |
| 296 outptr[2] = dcval; | |
| 297 outptr[3] = dcval; | |
| 298 outptr[4] = dcval; | |
| 299 outptr[5] = dcval; | |
| 300 outptr[6] = dcval; | |
| 301 outptr[7] = dcval; | |
| 302 | |
| 303 wsptr += DCTSIZE; /* advance pointer to next row */ | |
| 304 continue; | |
| 305 } | |
| 306 #endif | |
| 307 | |
| 308 /* Even part: reverse the even part of the forward DCT. */ | |
| 309 /* The rotator is sqrt(2)*c(-6). */ | |
| 310 | |
| 311 z2 = (INT32) wsptr[2]; | |
| 312 z3 = (INT32) wsptr[6]; | |
| 313 | |
| 314 z1 = MULTIPLY(z2 + z3, FIX_0_541196100); | |
| 315 tmp2 = z1 + MULTIPLY(z3, - FIX_1_847759065); | |
| 316 tmp3 = z1 + MULTIPLY(z2, FIX_0_765366865); | |
| 317 | |
| 318 tmp0 = ((INT32) wsptr[0] + (INT32) wsptr[4]) << CONST_BITS; | |
| 319 tmp1 = ((INT32) wsptr[0] - (INT32) wsptr[4]) << CONST_BITS; | |
| 320 | |
| 321 tmp10 = tmp0 + tmp3; | |
| 322 tmp13 = tmp0 - tmp3; | |
| 323 tmp11 = tmp1 + tmp2; | |
| 324 tmp12 = tmp1 - tmp2; | |
| 325 | |
| 326 /* Odd part per figure 8; the matrix is unitary and hence its | |
| 327 * transpose is its inverse. i0..i3 are y7,y5,y3,y1 respectively. | |
| 328 */ | |
| 329 | |
| 330 tmp0 = (INT32) wsptr[7]; | |
| 331 tmp1 = (INT32) wsptr[5]; | |
| 332 tmp2 = (INT32) wsptr[3]; | |
| 333 tmp3 = (INT32) wsptr[1]; | |
| 334 | |
| 335 z1 = tmp0 + tmp3; | |
| 336 z2 = tmp1 + tmp2; | |
| 337 z3 = tmp0 + tmp2; | |
| 338 z4 = tmp1 + tmp3; | |
| 339 z5 = MULTIPLY(z3 + z4, FIX_1_175875602); /* sqrt(2) * c3 */ | |
| 340 | |
| 341 tmp0 = MULTIPLY(tmp0, FIX_0_298631336); /* sqrt(2) * (-c1+c3+c5-c7) */ | |
| 342 tmp1 = MULTIPLY(tmp1, FIX_2_053119869); /* sqrt(2) * ( c1+c3-c5+c7) */ | |
| 343 tmp2 = MULTIPLY(tmp2, FIX_3_072711026); /* sqrt(2) * ( c1+c3+c5-c7) */ | |
| 344 tmp3 = MULTIPLY(tmp3, FIX_1_501321110); /* sqrt(2) * ( c1+c3-c5-c7) */ | |
| 345 z1 = MULTIPLY(z1, - FIX_0_899976223); /* sqrt(2) * (c7-c3) */ | |
| 346 z2 = MULTIPLY(z2, - FIX_2_562915447); /* sqrt(2) * (-c1-c3) */ | |
| 347 z3 = MULTIPLY(z3, - FIX_1_961570560); /* sqrt(2) * (-c3-c5) */ | |
| 348 z4 = MULTIPLY(z4, - FIX_0_390180644); /* sqrt(2) * (c5-c3) */ | |
| 349 | |
| 350 z3 += z5; | |
| 351 z4 += z5; | |
| 352 | |
| 353 tmp0 += z1 + z3; | |
| 354 tmp1 += z2 + z4; | |
| 355 tmp2 += z2 + z3; | |
| 356 tmp3 += z1 + z4; | |
| 357 | |
| 358 /* Final output stage: inputs are tmp10..tmp13, tmp0..tmp3 */ | |
| 359 | |
| 360 outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp3, | |
| 361 CONST_BITS+PASS1_BITS+3) | |
| 362 & RANGE_MASK]; | |
| 363 outptr[7] = range_limit[(int) DESCALE(tmp10 - tmp3, | |
| 364 CONST_BITS+PASS1_BITS+3) | |
| 365 & RANGE_MASK]; | |
| 366 outptr[1] = range_limit[(int) DESCALE(tmp11 + tmp2, | |
| 367 CONST_BITS+PASS1_BITS+3) | |
| 368 & RANGE_MASK]; | |
| 369 outptr[6] = range_limit[(int) DESCALE(tmp11 - tmp2, | |
| 370 CONST_BITS+PASS1_BITS+3) | |
| 371 & RANGE_MASK]; | |
| 372 outptr[2] = range_limit[(int) DESCALE(tmp12 + tmp1, | |
| 373 CONST_BITS+PASS1_BITS+3) | |
| 374 & RANGE_MASK]; | |
| 375 outptr[5] = range_limit[(int) DESCALE(tmp12 - tmp1, | |
| 376 CONST_BITS+PASS1_BITS+3) | |
| 377 & RANGE_MASK]; | |
| 378 outptr[3] = range_limit[(int) DESCALE(tmp13 + tmp0, | |
| 379 CONST_BITS+PASS1_BITS+3) | |
| 380 & RANGE_MASK]; | |
| 381 outptr[4] = range_limit[(int) DESCALE(tmp13 - tmp0, | |
| 382 CONST_BITS+PASS1_BITS+3) | |
| 383 & RANGE_MASK]; | |
| 384 | |
| 385 wsptr += DCTSIZE; /* advance pointer to next row */ | |
| 386 } | |
| 387 } | |
| 388 | |
| 389 #endif /* DCT_ISLOW_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