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, 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, 123 JSAMPARRAY output_buf, 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], quantptr[DCTSIZE*0]), 150 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] = (int) DESCALE(tmp10 + tmp2, CONST_BITS-PASS1_BITS+1); 193 wsptr[DCTSIZE*3] = (int) DESCALE(tmp10 - tmp2, CONST_BITS-PASS1_BITS+1); 194 wsptr[DCTSIZE*1] = (int) DESCALE(tmp12 + tmp0, CONST_BITS-PASS1_BITS+1); 195 wsptr[DCTSIZE*2] = (int) DESCALE(tmp12 - tmp0, CONST_BITS-PASS1_BITS+1); 196 } 197 198 /* Pass 2: process 4 rows from work array, store into output array. */ 199 200 wsptr = workspace; 201 for (ctr = 0; ctr < 4; ctr++) { 202 outptr = output_buf[ctr] + output_col; 203 /* It's not clear whether a zero row test is worthwhile here ... */ 204 205 #ifndef NO_ZERO_ROW_TEST 206 if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 && 207 wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) { 208 /* AC terms all zero */ 209 JSAMPLE dcval = range_limit[(int) DESCALE((JLONG) wsptr[0], PASS1_BITS+3) 210 & RANGE_MASK]; 211 212 outptr[0] = dcval; 213 outptr[1] = dcval; 214 outptr[2] = dcval; 215 outptr[3] = dcval; 216 217 wsptr += DCTSIZE; /* advance pointer to next row */ 218 continue; 219 } 220 #endif 221 222 /* Even part */ 223 224 tmp0 = LEFT_SHIFT((JLONG) wsptr[0], CONST_BITS+1); 225 226 tmp2 = MULTIPLY((JLONG) wsptr[2], FIX_1_847759065) 227 + MULTIPLY((JLONG) wsptr[6], - FIX_0_765366865); 228 229 tmp10 = tmp0 + tmp2; 230 tmp12 = tmp0 - tmp2; 231 232 /* Odd part */ 233 234 z1 = (JLONG) wsptr[7]; 235 z2 = (JLONG) wsptr[5]; 236 z3 = (JLONG) wsptr[3]; 237 z4 = (JLONG) wsptr[1]; 238 239 tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */ 240 + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */ 241 + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */ 242 + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */ 243 244 tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */ 245 + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */ 246 + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */ 247 + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */ 248 249 /* Final output stage */ 250 251 outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp2, 252 CONST_BITS+PASS1_BITS+3+1) 253 & RANGE_MASK]; 254 outptr[3] = range_limit[(int) DESCALE(tmp10 - tmp2, 255 CONST_BITS+PASS1_BITS+3+1) 256 & RANGE_MASK]; 257 outptr[1] = range_limit[(int) DESCALE(tmp12 + tmp0, 258 CONST_BITS+PASS1_BITS+3+1) 259 & RANGE_MASK]; 260 outptr[2] = range_limit[(int) DESCALE(tmp12 - tmp0, 261 CONST_BITS+PASS1_BITS+3+1) 262 & RANGE_MASK]; 263 264 wsptr += DCTSIZE; /* advance pointer to next row */ 265 } 266 } 267 268 269 /* 270 * Perform dequantization and inverse DCT on one block of coefficients, 271 * producing a reduced-size 2x2 output block. 272 */ 273 274 GLOBAL(void) 275 jpeg_idct_2x2 (j_decompress_ptr cinfo, jpeg_component_info *compptr, 276 JCOEFPTR coef_block, 277 JSAMPARRAY output_buf, JDIMENSION output_col) 278 { 279 JLONG tmp0, tmp10, z1; 280 JCOEFPTR inptr; 281 ISLOW_MULT_TYPE *quantptr; 282 int *wsptr; 283 JSAMPROW outptr; 284 JSAMPLE *range_limit = IDCT_range_limit(cinfo); 285 int ctr; 286 int workspace[DCTSIZE*2]; /* buffers data between passes */ 287 SHIFT_TEMPS 288 289 /* Pass 1: process columns from input, store into work array. */ 290 291 inptr = coef_block; 292 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table; 293 wsptr = workspace; 294 for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) { 295 /* Don't bother to process columns 2,4,6 */ 296 if (ctr == DCTSIZE-2 || ctr == DCTSIZE-4 || ctr == DCTSIZE-6) 297 continue; 298 if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*3] == 0 && 299 inptr[DCTSIZE*5] == 0 && inptr[DCTSIZE*7] == 0) { 300 /* AC terms all zero; we need not examine terms 2,4,6 for 2x2 output */ 301 int dcval = LEFT_SHIFT(DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]), 302 PASS1_BITS); 303 304 wsptr[DCTSIZE*0] = dcval; 305 wsptr[DCTSIZE*1] = dcval; 306 307 continue; 308 } 309 310 /* Even part */ 311 312 z1 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]); 313 tmp10 = LEFT_SHIFT(z1, CONST_BITS+2); 314 315 /* Odd part */ 316 317 z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]); 318 tmp0 = MULTIPLY(z1, - FIX_0_720959822); /* sqrt(2) * (c7-c5+c3-c1) */ 319 z1 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]); 320 tmp0 += MULTIPLY(z1, FIX_0_850430095); /* sqrt(2) * (-c1+c3+c5+c7) */ 321 z1 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]); 322 tmp0 += MULTIPLY(z1, - FIX_1_272758580); /* sqrt(2) * (-c1+c3-c5-c7) */ 323 z1 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]); 324 tmp0 += MULTIPLY(z1, FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */ 325 326 /* Final output stage */ 327 328 wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp0, CONST_BITS-PASS1_BITS+2); 329 wsptr[DCTSIZE*1] = (int) DESCALE(tmp10 - tmp0, CONST_BITS-PASS1_BITS+2); 330 } 331 332 /* Pass 2: process 2 rows from work array, store into output array. */ 333 334 wsptr = workspace; 335 for (ctr = 0; ctr < 2; ctr++) { 336 outptr = output_buf[ctr] + output_col; 337 /* It's not clear whether a zero row test is worthwhile here ... */ 338 339 #ifndef NO_ZERO_ROW_TEST 340 if (wsptr[1] == 0 && wsptr[3] == 0 && wsptr[5] == 0 && wsptr[7] == 0) { 341 /* AC terms all zero */ 342 JSAMPLE dcval = range_limit[(int) DESCALE((JLONG) wsptr[0], PASS1_BITS+3) 343 & RANGE_MASK]; 344 345 outptr[0] = dcval; 346 outptr[1] = dcval; 347 348 wsptr += DCTSIZE; /* advance pointer to next row */ 349 continue; 350 } 351 #endif 352 353 /* Even part */ 354 355 tmp10 = LEFT_SHIFT((JLONG) wsptr[0], CONST_BITS+2); 356 357 /* Odd part */ 358 359 tmp0 = MULTIPLY((JLONG) wsptr[7], - FIX_0_720959822) /* sqrt(2) * (c7-c5+c3-c1) */ 360 + MULTIPLY((JLONG) wsptr[5], FIX_0_850430095) /* sqrt(2) * (-c1+c3+c5+c7) */ 361 + MULTIPLY((JLONG) wsptr[3], - FIX_1_272758580) /* sqrt(2) * (-c1+c3-c5-c7) */ 362 + MULTIPLY((JLONG) wsptr[1], FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */ 363 364 /* Final output stage */ 365 366 outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp0, 367 CONST_BITS+PASS1_BITS+3+2) 368 & RANGE_MASK]; 369 outptr[1] = range_limit[(int) DESCALE(tmp10 - tmp0, 370 CONST_BITS+PASS1_BITS+3+2) 371 & RANGE_MASK]; 372 373 wsptr += DCTSIZE; /* advance pointer to next row */ 374 } 375 } 376 377 378 /* 379 * Perform dequantization and inverse DCT on one block of coefficients, 380 * producing a reduced-size 1x1 output block. 381 */ 382 383 GLOBAL(void) 384 jpeg_idct_1x1 (j_decompress_ptr cinfo, jpeg_component_info *compptr, 385 JCOEFPTR coef_block, 386 JSAMPARRAY output_buf, JDIMENSION output_col) 387 { 388 int dcval; 389 ISLOW_MULT_TYPE *quantptr; 390 JSAMPLE *range_limit = IDCT_range_limit(cinfo); 391 SHIFT_TEMPS 392 393 /* We hardly need an inverse DCT routine for this: just take the 394 * average pixel value, which is one-eighth of the DC coefficient. 395 */ 396 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table; 397 dcval = DEQUANTIZE(coef_block[0], quantptr[0]); 398 dcval = (int) DESCALE((JLONG) dcval, 3); 399 400 output_buf[0][output_col] = range_limit[dcval & RANGE_MASK]; 401 } 402 403 #endif /* IDCT_SCALING_SUPPORTED */ 404
