jidctred.c (14555B)
1 /* 2 * jidctred.c 3 * 4 * This file was part of the Independent JPEG Group's software: 5 * Copyright (C) 1994-1998, Thomas G. Lane. 6 * libjpeg-turbo Modifications: 7 * Copyright (C) 2015, 2022, D. R. Commander. 8 * For conditions of distribution and use, see the accompanying README.ijg 9 * file. 10 * 11 * This file contains inverse-DCT routines that produce reduced-size output: 12 * either 4x4, 2x2, or 1x1 pixels from an 8x8 DCT block. 13 * 14 * The implementation is based on the Loeffler, Ligtenberg and Moschytz (LL&M) 15 * algorithm used in jidctint.c. We simply replace each 8-to-8 1-D IDCT step 16 * with an 8-to-4 step that produces the four averages of two adjacent outputs 17 * (or an 8-to-2 step producing two averages of four outputs, for 2x2 output). 18 * These steps were derived by computing the corresponding values at the end 19 * of the normal LL&M code, then simplifying as much as possible. 20 * 21 * 1x1 is trivial: just take the DC coefficient divided by 8. 22 * 23 * See jidctint.c for additional comments. 24 */ 25 26 #define JPEG_INTERNALS 27 #include "jinclude.h" 28 #include "jpeglib.h" 29 #include "jdct.h" /* Private declarations for DCT subsystem */ 30 31 #ifdef IDCT_SCALING_SUPPORTED 32 33 34 /* 35 * This module is specialized to the case DCTSIZE = 8. 36 */ 37 38 #if DCTSIZE != 8 39 Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */ 40 #endif 41 42 43 /* Scaling is the same as in jidctint.c. */ 44 45 #if BITS_IN_JSAMPLE == 8 46 #define CONST_BITS 13 47 #define PASS1_BITS 2 48 #else 49 #define CONST_BITS 13 50 #define PASS1_BITS 1 /* lose a little precision to avoid overflow */ 51 #endif 52 53 /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus 54 * causing a lot of useless floating-point operations at run time. 55 * To get around this we use the following pre-calculated constants. 56 * If you change CONST_BITS you may want to add appropriate values. 57 * (With a reasonable C compiler, you can just rely on the FIX() macro...) 58 */ 59 60 #if CONST_BITS == 13 61 #define FIX_0_211164243 ((JLONG)1730) /* FIX(0.211164243) */ 62 #define FIX_0_509795579 ((JLONG)4176) /* FIX(0.509795579) */ 63 #define FIX_0_601344887 ((JLONG)4926) /* FIX(0.601344887) */ 64 #define FIX_0_720959822 ((JLONG)5906) /* FIX(0.720959822) */ 65 #define FIX_0_765366865 ((JLONG)6270) /* FIX(0.765366865) */ 66 #define FIX_0_850430095 ((JLONG)6967) /* FIX(0.850430095) */ 67 #define FIX_0_899976223 ((JLONG)7373) /* FIX(0.899976223) */ 68 #define FIX_1_061594337 ((JLONG)8697) /* FIX(1.061594337) */ 69 #define FIX_1_272758580 ((JLONG)10426) /* FIX(1.272758580) */ 70 #define FIX_1_451774981 ((JLONG)11893) /* FIX(1.451774981) */ 71 #define FIX_1_847759065 ((JLONG)15137) /* FIX(1.847759065) */ 72 #define FIX_2_172734803 ((JLONG)17799) /* FIX(2.172734803) */ 73 #define FIX_2_562915447 ((JLONG)20995) /* FIX(2.562915447) */ 74 #define FIX_3_624509785 ((JLONG)29692) /* FIX(3.624509785) */ 75 #else 76 #define FIX_0_211164243 FIX(0.211164243) 77 #define FIX_0_509795579 FIX(0.509795579) 78 #define FIX_0_601344887 FIX(0.601344887) 79 #define FIX_0_720959822 FIX(0.720959822) 80 #define FIX_0_765366865 FIX(0.765366865) 81 #define FIX_0_850430095 FIX(0.850430095) 82 #define FIX_0_899976223 FIX(0.899976223) 83 #define FIX_1_061594337 FIX(1.061594337) 84 #define FIX_1_272758580 FIX(1.272758580) 85 #define FIX_1_451774981 FIX(1.451774981) 86 #define FIX_1_847759065 FIX(1.847759065) 87 #define FIX_2_172734803 FIX(2.172734803) 88 #define FIX_2_562915447 FIX(2.562915447) 89 #define FIX_3_624509785 FIX(3.624509785) 90 #endif 91 92 93 /* Multiply a JLONG variable by a JLONG constant to yield a JLONG result. 94 * For 8-bit samples with the recommended scaling, all the variable 95 * and constant values involved are no more than 16 bits wide, so a 96 * 16x16->32 bit multiply can be used instead of a full 32x32 multiply. 97 * For 12-bit samples, a full 32-bit multiplication will be needed. 98 */ 99 100 #if BITS_IN_JSAMPLE == 8 101 #define MULTIPLY(var, const) MULTIPLY16C16(var, const) 102 #else 103 #define MULTIPLY(var, const) ((var) * (const)) 104 #endif 105 106 107 /* Dequantize a coefficient by multiplying it by the multiplier-table 108 * entry; produce an int result. In this module, both inputs and result 109 * are 16 bits or less, so either int or short multiply will work. 110 */ 111 112 #define DEQUANTIZE(coef, quantval) (((ISLOW_MULT_TYPE)(coef)) * (quantval)) 113 114 115 /* 116 * Perform dequantization and inverse DCT on one block of coefficients, 117 * producing a reduced-size 4x4 output block. 118 */ 119 120 GLOBAL(void) 121 _jpeg_idct_4x4(j_decompress_ptr cinfo, jpeg_component_info *compptr, 122 JCOEFPTR coef_block, _JSAMPARRAY output_buf, 123 JDIMENSION output_col) 124 { 125 JLONG tmp0, tmp2, tmp10, tmp12; 126 JLONG z1, z2, z3, z4; 127 JCOEFPTR inptr; 128 ISLOW_MULT_TYPE *quantptr; 129 int *wsptr; 130 _JSAMPROW outptr; 131 _JSAMPLE *range_limit = IDCT_range_limit(cinfo); 132 int ctr; 133 int workspace[DCTSIZE * 4]; /* buffers data between passes */ 134 SHIFT_TEMPS 135 136 /* Pass 1: process columns from input, store into work array. */ 137 138 inptr = coef_block; 139 quantptr = (ISLOW_MULT_TYPE *)compptr->dct_table; 140 wsptr = workspace; 141 for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) { 142 /* Don't bother to process column 4, because second pass won't use it */ 143 if (ctr == DCTSIZE - 4) 144 continue; 145 if (inptr[DCTSIZE * 1] == 0 && inptr[DCTSIZE * 2] == 0 && 146 inptr[DCTSIZE * 3] == 0 && inptr[DCTSIZE * 5] == 0 && 147 inptr[DCTSIZE * 6] == 0 && inptr[DCTSIZE * 7] == 0) { 148 /* AC terms all zero; we need not examine term 4 for 4x4 output */ 149 int dcval = LEFT_SHIFT(DEQUANTIZE(inptr[DCTSIZE * 0], 150 quantptr[DCTSIZE * 0]), PASS1_BITS); 151 152 wsptr[DCTSIZE * 0] = dcval; 153 wsptr[DCTSIZE * 1] = dcval; 154 wsptr[DCTSIZE * 2] = dcval; 155 wsptr[DCTSIZE * 3] = dcval; 156 157 continue; 158 } 159 160 /* Even part */ 161 162 tmp0 = DEQUANTIZE(inptr[DCTSIZE * 0], quantptr[DCTSIZE * 0]); 163 tmp0 = LEFT_SHIFT(tmp0, CONST_BITS + 1); 164 165 z2 = DEQUANTIZE(inptr[DCTSIZE * 2], quantptr[DCTSIZE * 2]); 166 z3 = DEQUANTIZE(inptr[DCTSIZE * 6], quantptr[DCTSIZE * 6]); 167 168 tmp2 = MULTIPLY(z2, FIX_1_847759065) + MULTIPLY(z3, -FIX_0_765366865); 169 170 tmp10 = tmp0 + tmp2; 171 tmp12 = tmp0 - tmp2; 172 173 /* Odd part */ 174 175 z1 = DEQUANTIZE(inptr[DCTSIZE * 7], quantptr[DCTSIZE * 7]); 176 z2 = DEQUANTIZE(inptr[DCTSIZE * 5], quantptr[DCTSIZE * 5]); 177 z3 = DEQUANTIZE(inptr[DCTSIZE * 3], quantptr[DCTSIZE * 3]); 178 z4 = DEQUANTIZE(inptr[DCTSIZE * 1], quantptr[DCTSIZE * 1]); 179 180 tmp0 = MULTIPLY(z1, -FIX_0_211164243) + /* sqrt(2) * ( c3-c1) */ 181 MULTIPLY(z2, FIX_1_451774981) + /* sqrt(2) * ( c3+c7) */ 182 MULTIPLY(z3, -FIX_2_172734803) + /* sqrt(2) * (-c1-c5) */ 183 MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * ( c5+c7) */ 184 185 tmp2 = MULTIPLY(z1, -FIX_0_509795579) + /* sqrt(2) * (c7-c5) */ 186 MULTIPLY(z2, -FIX_0_601344887) + /* sqrt(2) * (c5-c1) */ 187 MULTIPLY(z3, FIX_0_899976223) + /* sqrt(2) * (c3-c7) */ 188 MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */ 189 190 /* Final output stage */ 191 192 wsptr[DCTSIZE * 0] = 193 (int)DESCALE(tmp10 + tmp2, CONST_BITS - PASS1_BITS + 1); 194 wsptr[DCTSIZE * 3] = 195 (int)DESCALE(tmp10 - tmp2, CONST_BITS - PASS1_BITS + 1); 196 wsptr[DCTSIZE * 1] = 197 (int)DESCALE(tmp12 + tmp0, CONST_BITS - PASS1_BITS + 1); 198 wsptr[DCTSIZE * 2] = 199 (int)DESCALE(tmp12 - tmp0, CONST_BITS - PASS1_BITS + 1); 200 } 201 202 /* Pass 2: process 4 rows from work array, store into output array. */ 203 204 wsptr = workspace; 205 for (ctr = 0; ctr < 4; ctr++) { 206 outptr = output_buf[ctr] + output_col; 207 /* It's not clear whether a zero row test is worthwhile here ... */ 208 209 #ifndef NO_ZERO_ROW_TEST 210 if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 && 211 wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) { 212 /* AC terms all zero */ 213 _JSAMPLE dcval = range_limit[(int)DESCALE((JLONG)wsptr[0], 214 PASS1_BITS + 3) & RANGE_MASK]; 215 216 outptr[0] = dcval; 217 outptr[1] = dcval; 218 outptr[2] = dcval; 219 outptr[3] = dcval; 220 221 wsptr += DCTSIZE; /* advance pointer to next row */ 222 continue; 223 } 224 #endif 225 226 /* Even part */ 227 228 tmp0 = LEFT_SHIFT((JLONG)wsptr[0], CONST_BITS + 1); 229 230 tmp2 = MULTIPLY((JLONG)wsptr[2], FIX_1_847759065) + 231 MULTIPLY((JLONG)wsptr[6], -FIX_0_765366865); 232 233 tmp10 = tmp0 + tmp2; 234 tmp12 = tmp0 - tmp2; 235 236 /* Odd part */ 237 238 z1 = (JLONG)wsptr[7]; 239 z2 = (JLONG)wsptr[5]; 240 z3 = (JLONG)wsptr[3]; 241 z4 = (JLONG)wsptr[1]; 242 243 tmp0 = MULTIPLY(z1, -FIX_0_211164243) + /* sqrt(2) * ( c3-c1) */ 244 MULTIPLY(z2, FIX_1_451774981) + /* sqrt(2) * ( c3+c7) */ 245 MULTIPLY(z3, -FIX_2_172734803) + /* sqrt(2) * (-c1-c5) */ 246 MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * ( c5+c7) */ 247 248 tmp2 = MULTIPLY(z1, -FIX_0_509795579) + /* sqrt(2) * (c7-c5) */ 249 MULTIPLY(z2, -FIX_0_601344887) + /* sqrt(2) * (c5-c1) */ 250 MULTIPLY(z3, FIX_0_899976223) + /* sqrt(2) * (c3-c7) */ 251 MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */ 252 253 /* Final output stage */ 254 255 outptr[0] = range_limit[(int)DESCALE(tmp10 + tmp2, 256 CONST_BITS + PASS1_BITS + 3 + 1) & 257 RANGE_MASK]; 258 outptr[3] = range_limit[(int)DESCALE(tmp10 - tmp2, 259 CONST_BITS + PASS1_BITS + 3 + 1) & 260 RANGE_MASK]; 261 outptr[1] = range_limit[(int)DESCALE(tmp12 + tmp0, 262 CONST_BITS + PASS1_BITS + 3 + 1) & 263 RANGE_MASK]; 264 outptr[2] = range_limit[(int)DESCALE(tmp12 - tmp0, 265 CONST_BITS + PASS1_BITS + 3 + 1) & 266 RANGE_MASK]; 267 268 wsptr += DCTSIZE; /* advance pointer to next row */ 269 } 270 } 271 272 273 /* 274 * Perform dequantization and inverse DCT on one block of coefficients, 275 * producing a reduced-size 2x2 output block. 276 */ 277 278 GLOBAL(void) 279 _jpeg_idct_2x2(j_decompress_ptr cinfo, jpeg_component_info *compptr, 280 JCOEFPTR coef_block, _JSAMPARRAY output_buf, 281 JDIMENSION output_col) 282 { 283 JLONG tmp0, tmp10, z1; 284 JCOEFPTR inptr; 285 ISLOW_MULT_TYPE *quantptr; 286 int *wsptr; 287 _JSAMPROW outptr; 288 _JSAMPLE *range_limit = IDCT_range_limit(cinfo); 289 int ctr; 290 int workspace[DCTSIZE * 2]; /* buffers data between passes */ 291 SHIFT_TEMPS 292 293 /* Pass 1: process columns from input, store into work array. */ 294 295 inptr = coef_block; 296 quantptr = (ISLOW_MULT_TYPE *)compptr->dct_table; 297 wsptr = workspace; 298 for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) { 299 /* Don't bother to process columns 2,4,6 */ 300 if (ctr == DCTSIZE - 2 || ctr == DCTSIZE - 4 || ctr == DCTSIZE - 6) 301 continue; 302 if (inptr[DCTSIZE * 1] == 0 && inptr[DCTSIZE * 3] == 0 && 303 inptr[DCTSIZE * 5] == 0 && inptr[DCTSIZE * 7] == 0) { 304 /* AC terms all zero; we need not examine terms 2,4,6 for 2x2 output */ 305 int dcval = LEFT_SHIFT(DEQUANTIZE(inptr[DCTSIZE * 0], 306 quantptr[DCTSIZE * 0]), PASS1_BITS); 307 308 wsptr[DCTSIZE * 0] = dcval; 309 wsptr[DCTSIZE * 1] = dcval; 310 311 continue; 312 } 313 314 /* Even part */ 315 316 z1 = DEQUANTIZE(inptr[DCTSIZE * 0], quantptr[DCTSIZE * 0]); 317 tmp10 = LEFT_SHIFT(z1, CONST_BITS + 2); 318 319 /* Odd part */ 320 321 z1 = DEQUANTIZE(inptr[DCTSIZE * 7], quantptr[DCTSIZE * 7]); 322 tmp0 = MULTIPLY(z1, -FIX_0_720959822); /* sqrt(2) * ( c7-c5+c3-c1) */ 323 z1 = DEQUANTIZE(inptr[DCTSIZE * 5], quantptr[DCTSIZE * 5]); 324 tmp0 += MULTIPLY(z1, FIX_0_850430095); /* sqrt(2) * (-c1+c3+c5+c7) */ 325 z1 = DEQUANTIZE(inptr[DCTSIZE * 3], quantptr[DCTSIZE * 3]); 326 tmp0 += MULTIPLY(z1, -FIX_1_272758580); /* sqrt(2) * (-c1+c3-c5-c7) */ 327 z1 = DEQUANTIZE(inptr[DCTSIZE * 1], quantptr[DCTSIZE * 1]); 328 tmp0 += MULTIPLY(z1, FIX_3_624509785); /* sqrt(2) * ( c1+c3+c5+c7) */ 329 330 /* Final output stage */ 331 332 wsptr[DCTSIZE * 0] = 333 (int)DESCALE(tmp10 + tmp0, CONST_BITS - PASS1_BITS + 2); 334 wsptr[DCTSIZE * 1] = 335 (int)DESCALE(tmp10 - tmp0, CONST_BITS - PASS1_BITS + 2); 336 } 337 338 /* Pass 2: process 2 rows from work array, store into output array. */ 339 340 wsptr = workspace; 341 for (ctr = 0; ctr < 2; ctr++) { 342 outptr = output_buf[ctr] + output_col; 343 /* It's not clear whether a zero row test is worthwhile here ... */ 344 345 #ifndef NO_ZERO_ROW_TEST 346 if (wsptr[1] == 0 && wsptr[3] == 0 && wsptr[5] == 0 && wsptr[7] == 0) { 347 /* AC terms all zero */ 348 _JSAMPLE dcval = range_limit[(int)DESCALE((JLONG)wsptr[0], 349 PASS1_BITS + 3) & RANGE_MASK]; 350 351 outptr[0] = dcval; 352 outptr[1] = dcval; 353 354 wsptr += DCTSIZE; /* advance pointer to next row */ 355 continue; 356 } 357 #endif 358 359 /* Even part */ 360 361 tmp10 = LEFT_SHIFT((JLONG)wsptr[0], CONST_BITS + 2); 362 363 /* Odd part */ 364 365 tmp0 = MULTIPLY((JLONG)wsptr[7], -FIX_0_720959822) + /* sqrt(2) * ( c7-c5+c3-c1) */ 366 MULTIPLY((JLONG)wsptr[5], FIX_0_850430095) + /* sqrt(2) * (-c1+c3+c5+c7) */ 367 MULTIPLY((JLONG)wsptr[3], -FIX_1_272758580) + /* sqrt(2) * (-c1+c3-c5-c7) */ 368 MULTIPLY((JLONG)wsptr[1], FIX_3_624509785); /* sqrt(2) * ( c1+c3+c5+c7) */ 369 370 /* Final output stage */ 371 372 outptr[0] = range_limit[(int)DESCALE(tmp10 + tmp0, 373 CONST_BITS + PASS1_BITS + 3 + 2) & 374 RANGE_MASK]; 375 outptr[1] = range_limit[(int)DESCALE(tmp10 - tmp0, 376 CONST_BITS + PASS1_BITS + 3 + 2) & 377 RANGE_MASK]; 378 379 wsptr += DCTSIZE; /* advance pointer to next row */ 380 } 381 } 382 383 384 /* 385 * Perform dequantization and inverse DCT on one block of coefficients, 386 * producing a reduced-size 1x1 output block. 387 */ 388 389 GLOBAL(void) 390 _jpeg_idct_1x1(j_decompress_ptr cinfo, jpeg_component_info *compptr, 391 JCOEFPTR coef_block, _JSAMPARRAY output_buf, 392 JDIMENSION output_col) 393 { 394 int dcval; 395 ISLOW_MULT_TYPE *quantptr; 396 _JSAMPLE *range_limit = IDCT_range_limit(cinfo); 397 SHIFT_TEMPS 398 399 /* We hardly need an inverse DCT routine for this: just take the 400 * average pixel value, which is one-eighth of the DC coefficient. 401 */ 402 quantptr = (ISLOW_MULT_TYPE *)compptr->dct_table; 403 dcval = DEQUANTIZE(coef_block[0], quantptr[0]); 404 dcval = (int)DESCALE((JLONG)dcval, 3); 405 406 output_buf[0][output_col] = range_limit[dcval & RANGE_MASK]; 407 } 408 409 #endif /* IDCT_SCALING_SUPPORTED */