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 file. 9 * 10 * This file contains inverse-DCT routines that produce reduced-size output: 11 * either 4x4, 2x2, or 1x1 pixels from an 8x8 DCT block. 12 * 13 * The implementation is based on the Loeffler, Ligtenberg and Moschytz (LL&M) 14 * algorithm used in jidctint.c. We simply replace each 8-to-8 1-D IDCT step 15 * with an 8-to-4 step that produces the four averages of two adjacent outputs 16 * (or an 8-to-2 step producing two averages of four outputs, for 2x2 output). 17 * These steps were derived by computing the corresponding values at the end 18 * of the normal LL&M code, then simplifying as much as possible. 19 * 20 * 1x1 is trivial: just take the DC coefficient divided by 8. 21 * 22 * See jidctint.c for additional comments. 23 */ 24 25 #define JPEG_INTERNALS 26 #include "jinclude.h" 27 #include "jpeglib.h" 28 #include "jdct.h" /* Private declarations for DCT subsystem */ 29 30 #ifdef IDCT_SCALING_SUPPORTED 31 32 33 /* 34 * This module is specialized to the case DCTSIZE = 8. 35 */ 36 37 #if DCTSIZE != 8 38 Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */ 39 #endif 40 41 42 /* Scaling is the same as in jidctint.c. */ 43 44 #if BITS_IN_JSAMPLE == 8 45 #define CONST_BITS 13 46 #define PASS1_BITS 2 47 #else 48 #define CONST_BITS 13 49 #define PASS1_BITS 1 /* lose a little precision to avoid overflow */ 50 #endif 51 52 /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus 53 * causing a lot of useless floating-point operations at run time. 54 * To get around this we use the following pre-calculated constants. 55 * If you change CONST_BITS you may want to add appropriate values. 56 * (With a reasonable C compiler, you can just rely on the FIX() macro...) 57 */ 58 59 #if CONST_BITS == 13 60 #define FIX_0_211164243 ((INT32) 1730) /* FIX(0.211164243) */ 61 #define FIX_0_509795579 ((INT32) 4176) /* FIX(0.509795579) */ 62 #define FIX_0_601344887 ((INT32) 4926) /* FIX(0.601344887) */ 63 #define FIX_0_720959822 ((INT32) 5906) /* FIX(0.720959822) */ 64 #define FIX_0_765366865 ((INT32) 6270) /* FIX(0.765366865) */ 65 #define FIX_0_850430095 ((INT32) 6967) /* FIX(0.850430095) */ 66 #define FIX_0_899976223 ((INT32) 7373) /* FIX(0.899976223) */ 67 #define FIX_1_061594337 ((INT32) 8697) /* FIX(1.061594337) */ 68 #define FIX_1_272758580 ((INT32) 10426) /* FIX(1.272758580) */ 69 #define FIX_1_451774981 ((INT32) 11893) /* FIX(1.451774981) */ 70 #define FIX_1_847759065 ((INT32) 15137) /* FIX(1.847759065) */ 71 #define FIX_2_172734803 ((INT32) 17799) /* FIX(2.172734803) */ 72 #define FIX_2_562915447 ((INT32) 20995) /* FIX(2.562915447) */ 73 #define FIX_3_624509785 ((INT32) 29692) /* FIX(3.624509785) */ 74 #else 75 #define FIX_0_211164243 FIX(0.211164243) 76 #define FIX_0_509795579 FIX(0.509795579) 77 #define FIX_0_601344887 FIX(0.601344887) 78 #define FIX_0_720959822 FIX(0.720959822) 79 #define FIX_0_765366865 FIX(0.765366865) 80 #define FIX_0_850430095 FIX(0.850430095) 81 #define FIX_0_899976223 FIX(0.899976223) 82 #define FIX_1_061594337 FIX(1.061594337) 83 #define FIX_1_272758580 FIX(1.272758580) 84 #define FIX_1_451774981 FIX(1.451774981) 85 #define FIX_1_847759065 FIX(1.847759065) 86 #define FIX_2_172734803 FIX(2.172734803) 87 #define FIX_2_562915447 FIX(2.562915447) 88 #define FIX_3_624509785 FIX(3.624509785) 89 #endif 90 91 92 /* Multiply an INT32 variable by an INT32 constant to yield an INT32 result. 93 * For 8-bit samples with the recommended scaling, all the variable 94 * and constant values involved are no more than 16 bits wide, so a 95 * 16x16->32 bit multiply can be used instead of a full 32x32 multiply. 96 * For 12-bit samples, a full 32-bit multiplication will be needed. 97 */ 98 99 #if BITS_IN_JSAMPLE == 8 100 #define MULTIPLY(var,const) MULTIPLY16C16(var,const) 101 #else 102 #define MULTIPLY(var,const) ((var) * (const)) 103 #endif 104 105 106 /* Dequantize a coefficient by multiplying it by the multiplier-table 107 * entry; produce an int result. In this module, both inputs and result 108 * are 16 bits or less, so either int or short multiply will work. 109 */ 110 111 #define DEQUANTIZE(coef,quantval) (((ISLOW_MULT_TYPE) (coef)) * (quantval)) 112 113 114 /* 115 * Perform dequantization and inverse DCT on one block of coefficients, 116 * producing a reduced-size 4x4 output block. 117 */ 118 119 GLOBAL(void) 120 jpeg_idct_4x4 (j_decompress_ptr cinfo, jpeg_component_info * compptr, 121 JCOEFPTR coef_block, 122 JSAMPARRAY output_buf, JDIMENSION output_col) 123 { 124 INT32 tmp0, tmp2, tmp10, tmp12; 125 INT32 z1, z2, z3, z4; 126 JCOEFPTR inptr; 127 ISLOW_MULT_TYPE * quantptr; 128 int * wsptr; 129 JSAMPROW outptr; 130 JSAMPLE *range_limit = IDCT_range_limit(cinfo); 131 int ctr; 132 int workspace[DCTSIZE*4]; /* buffers data between passes */ 133 SHIFT_TEMPS 134 135 /* Pass 1: process columns from input, store into work array. */ 136 137 inptr = coef_block; 138 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table; 139 wsptr = workspace; 140 for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) { 141 /* Don't bother to process column 4, because second pass won't use it */ 142 if (ctr == DCTSIZE-4) 143 continue; 144 if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 && 145 inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*5] == 0 && 146 inptr[DCTSIZE*6] == 0 && inptr[DCTSIZE*7] == 0) { 147 /* AC terms all zero; we need not examine term 4 for 4x4 output */ 148 int dcval = LEFT_SHIFT(DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]), 149 PASS1_BITS); 150 151 wsptr[DCTSIZE*0] = dcval; 152 wsptr[DCTSIZE*1] = dcval; 153 wsptr[DCTSIZE*2] = dcval; 154 wsptr[DCTSIZE*3] = dcval; 155 156 continue; 157 } 158 159 /* Even part */ 160 161 tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]); 162 tmp0 = LEFT_SHIFT(tmp0, CONST_BITS+1); 163 164 z2 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]); 165 z3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]); 166 167 tmp2 = MULTIPLY(z2, FIX_1_847759065) + MULTIPLY(z3, - FIX_0_765366865); 168 169 tmp10 = tmp0 + tmp2; 170 tmp12 = tmp0 - tmp2; 171 172 /* Odd part */ 173 174 z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]); 175 z2 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]); 176 z3 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]); 177 z4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]); 178 179 tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */ 180 + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */ 181 + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */ 182 + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */ 183 184 tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */ 185 + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */ 186 + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */ 187 + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */ 188 189 /* Final output stage */ 190 191 wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp2, CONST_BITS-PASS1_BITS+1); 192 wsptr[DCTSIZE*3] = (int) DESCALE(tmp10 - tmp2, CONST_BITS-PASS1_BITS+1); 193 wsptr[DCTSIZE*1] = (int) DESCALE(tmp12 + tmp0, CONST_BITS-PASS1_BITS+1); 194 wsptr[DCTSIZE*2] = (int) DESCALE(tmp12 - tmp0, CONST_BITS-PASS1_BITS+1); 195 } 196 197 /* Pass 2: process 4 rows from work array, store into output array. */ 198 199 wsptr = workspace; 200 for (ctr = 0; ctr < 4; ctr++) { 201 outptr = output_buf[ctr] + output_col; 202 /* It's not clear whether a zero row test is worthwhile here ... */ 203 204 #ifndef NO_ZERO_ROW_TEST 205 if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 && 206 wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) { 207 /* AC terms all zero */ 208 JSAMPLE dcval = range_limit[(int) DESCALE((INT32) wsptr[0], PASS1_BITS+3) 209 & RANGE_MASK]; 210 211 outptr[0] = dcval; 212 outptr[1] = dcval; 213 outptr[2] = dcval; 214 outptr[3] = dcval; 215 216 wsptr += DCTSIZE; /* advance pointer to next row */ 217 continue; 218 } 219 #endif 220 221 /* Even part */ 222 223 tmp0 = LEFT_SHIFT((INT32) wsptr[0], CONST_BITS+1); 224 225 tmp2 = MULTIPLY((INT32) wsptr[2], FIX_1_847759065) 226 + MULTIPLY((INT32) wsptr[6], - FIX_0_765366865); 227 228 tmp10 = tmp0 + tmp2; 229 tmp12 = tmp0 - tmp2; 230 231 /* Odd part */ 232 233 z1 = (INT32) wsptr[7]; 234 z2 = (INT32) wsptr[5]; 235 z3 = (INT32) wsptr[3]; 236 z4 = (INT32) wsptr[1]; 237 238 tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */ 239 + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */ 240 + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */ 241 + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */ 242 243 tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */ 244 + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */ 245 + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */ 246 + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */ 247 248 /* Final output stage */ 249 250 outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp2, 251 CONST_BITS+PASS1_BITS+3+1) 252 & RANGE_MASK]; 253 outptr[3] = range_limit[(int) DESCALE(tmp10 - tmp2, 254 CONST_BITS+PASS1_BITS+3+1) 255 & RANGE_MASK]; 256 outptr[1] = range_limit[(int) DESCALE(tmp12 + tmp0, 257 CONST_BITS+PASS1_BITS+3+1) 258 & RANGE_MASK]; 259 outptr[2] = range_limit[(int) DESCALE(tmp12 - tmp0, 260 CONST_BITS+PASS1_BITS+3+1) 261 & RANGE_MASK]; 262 263 wsptr += DCTSIZE; /* advance pointer to next row */ 264 } 265 } 266 267 268 /* 269 * Perform dequantization and inverse DCT on one block of coefficients, 270 * producing a reduced-size 2x2 output block. 271 */ 272 273 GLOBAL(void) 274 jpeg_idct_2x2 (j_decompress_ptr cinfo, jpeg_component_info * compptr, 275 JCOEFPTR coef_block, 276 JSAMPARRAY output_buf, JDIMENSION output_col) 277 { 278 INT32 tmp0, tmp10, z1; 279 JCOEFPTR inptr; 280 ISLOW_MULT_TYPE * quantptr; 281 int * wsptr; 282 JSAMPROW outptr; 283 JSAMPLE *range_limit = IDCT_range_limit(cinfo); 284 int ctr; 285 int workspace[DCTSIZE*2]; /* buffers data between passes */ 286 SHIFT_TEMPS 287 288 /* Pass 1: process columns from input, store into work array. */ 289 290 inptr = coef_block; 291 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table; 292 wsptr = workspace; 293 for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) { 294 /* Don't bother to process columns 2,4,6 */ 295 if (ctr == DCTSIZE-2 || ctr == DCTSIZE-4 || ctr == DCTSIZE-6) 296 continue; 297 if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*3] == 0 && 298 inptr[DCTSIZE*5] == 0 && inptr[DCTSIZE*7] == 0) { 299 /* AC terms all zero; we need not examine terms 2,4,6 for 2x2 output */ 300 int dcval = LEFT_SHIFT(DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]), 301 PASS1_BITS); 302 303 wsptr[DCTSIZE*0] = dcval; 304 wsptr[DCTSIZE*1] = dcval; 305 306 continue; 307 } 308 309 /* Even part */ 310 311 z1 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]); 312 tmp10 = LEFT_SHIFT(z1, CONST_BITS+2); 313 314 /* Odd part */ 315 316 z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]); 317 tmp0 = MULTIPLY(z1, - FIX_0_720959822); /* sqrt(2) * (c7-c5+c3-c1) */ 318 z1 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]); 319 tmp0 += MULTIPLY(z1, FIX_0_850430095); /* sqrt(2) * (-c1+c3+c5+c7) */ 320 z1 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]); 321 tmp0 += MULTIPLY(z1, - FIX_1_272758580); /* sqrt(2) * (-c1+c3-c5-c7) */ 322 z1 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]); 323 tmp0 += MULTIPLY(z1, FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */ 324 325 /* Final output stage */ 326 327 wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp0, CONST_BITS-PASS1_BITS+2); 328 wsptr[DCTSIZE*1] = (int) DESCALE(tmp10 - tmp0, CONST_BITS-PASS1_BITS+2); 329 } 330 331 /* Pass 2: process 2 rows from work array, store into output array. */ 332 333 wsptr = workspace; 334 for (ctr = 0; ctr < 2; ctr++) { 335 outptr = output_buf[ctr] + output_col; 336 /* It's not clear whether a zero row test is worthwhile here ... */ 337 338 #ifndef NO_ZERO_ROW_TEST 339 if (wsptr[1] == 0 && wsptr[3] == 0 && wsptr[5] == 0 && wsptr[7] == 0) { 340 /* AC terms all zero */ 341 JSAMPLE dcval = range_limit[(int) DESCALE((INT32) wsptr[0], PASS1_BITS+3) 342 & RANGE_MASK]; 343 344 outptr[0] = dcval; 345 outptr[1] = dcval; 346 347 wsptr += DCTSIZE; /* advance pointer to next row */ 348 continue; 349 } 350 #endif 351 352 /* Even part */ 353 354 tmp10 = LEFT_SHIFT((INT32) wsptr[0], CONST_BITS+2); 355 356 /* Odd part */ 357 358 tmp0 = MULTIPLY((INT32) wsptr[7], - FIX_0_720959822) /* sqrt(2) * (c7-c5+c3-c1) */ 359 + MULTIPLY((INT32) wsptr[5], FIX_0_850430095) /* sqrt(2) * (-c1+c3+c5+c7) */ 360 + MULTIPLY((INT32) wsptr[3], - FIX_1_272758580) /* sqrt(2) * (-c1+c3-c5-c7) */ 361 + MULTIPLY((INT32) wsptr[1], FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */ 362 363 /* Final output stage */ 364 365 outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp0, 366 CONST_BITS+PASS1_BITS+3+2) 367 & RANGE_MASK]; 368 outptr[1] = range_limit[(int) DESCALE(tmp10 - tmp0, 369 CONST_BITS+PASS1_BITS+3+2) 370 & RANGE_MASK]; 371 372 wsptr += DCTSIZE; /* advance pointer to next row */ 373 } 374 } 375 376 377 /* 378 * Perform dequantization and inverse DCT on one block of coefficients, 379 * producing a reduced-size 1x1 output block. 380 */ 381 382 GLOBAL(void) 383 jpeg_idct_1x1 (j_decompress_ptr cinfo, jpeg_component_info * compptr, 384 JCOEFPTR coef_block, 385 JSAMPARRAY output_buf, JDIMENSION output_col) 386 { 387 int dcval; 388 ISLOW_MULT_TYPE * quantptr; 389 JSAMPLE *range_limit = IDCT_range_limit(cinfo); 390 SHIFT_TEMPS 391 392 /* We hardly need an inverse DCT routine for this: just take the 393 * average pixel value, which is one-eighth of the DC coefficient. 394 */ 395 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table; 396 dcval = DEQUANTIZE(coef_block[0], quantptr[0]); 397 dcval = (int) DESCALE((INT32) dcval, 3); 398 399 output_buf[0][output_col] = range_limit[dcval & RANGE_MASK]; 400 } 401 402 #endif /* IDCT_SCALING_SUPPORTED */ 403
