1/* 2 * reserved comment block 3 * DO NOT REMOVE OR ALTER! 4 */ 5/* 6 * jidctred.c 7 * 8 * Copyright (C) 1994-1998, Thomas G. Lane. 9 * This file is part of the Independent JPEG Group's software. 10 * For conditions of distribution and use, see the accompanying README file. 11 * 12 * This file contains inverse-DCT routines that produce reduced-size output: 13 * either 4x4, 2x2, or 1x1 pixels from an 8x8 DCT block. 14 * 15 * The implementation is based on the Loeffler, Ligtenberg and Moschytz (LL&M) 16 * algorithm used in jidctint.c. We simply replace each 8-to-8 1-D IDCT step 17 * with an 8-to-4 step that produces the four averages of two adjacent outputs 18 * (or an 8-to-2 step producing two averages of four outputs, for 2x2 output). 19 * These steps were derived by computing the corresponding values at the end 20 * of the normal LL&M code, then simplifying as much as possible. 21 * 22 * 1x1 is trivial: just take the DC coefficient divided by 8. 23 * 24 * See jidctint.c for additional comments. 25 */ 26 27#define JPEG_INTERNALS 28#include "jinclude.h" 29#include "jpeglib.h" 30#include "jdct.h" /* Private declarations for DCT subsystem */ 31 32#ifdef IDCT_SCALING_SUPPORTED 33 34 35/* 36 * This module is specialized to the case DCTSIZE = 8. 37 */ 38 39#if DCTSIZE != 8 40 Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */ 41#endif 42 43 44/* Scaling is the same as in jidctint.c. */ 45 46#if BITS_IN_JSAMPLE == 8 47#define CONST_BITS 13 48#define PASS1_BITS 2 49#else 50#define CONST_BITS 13 51#define PASS1_BITS 1 /* lose a little precision to avoid overflow */ 52#endif 53 54/* Some C compilers fail to reduce "FIX(constant)" at compile time, thus 55 * causing a lot of useless floating-point operations at run time. 56 * To get around this we use the following pre-calculated constants. 57 * If you change CONST_BITS you may want to add appropriate values. 58 * (With a reasonable C compiler, you can just rely on the FIX() macro...) 59 */ 60 61#if CONST_BITS == 13 62#define FIX_0_211164243 ((INT32) 1730) /* FIX(0.211164243) */ 63#define FIX_0_509795579 ((INT32) 4176) /* FIX(0.509795579) */ 64#define FIX_0_601344887 ((INT32) 4926) /* FIX(0.601344887) */ 65#define FIX_0_720959822 ((INT32) 5906) /* FIX(0.720959822) */ 66#define FIX_0_765366865 ((INT32) 6270) /* FIX(0.765366865) */ 67#define FIX_0_850430095 ((INT32) 6967) /* FIX(0.850430095) */ 68#define FIX_0_899976223 ((INT32) 7373) /* FIX(0.899976223) */ 69#define FIX_1_061594337 ((INT32) 8697) /* FIX(1.061594337) */ 70#define FIX_1_272758580 ((INT32) 10426) /* FIX(1.272758580) */ 71#define FIX_1_451774981 ((INT32) 11893) /* FIX(1.451774981) */ 72#define FIX_1_847759065 ((INT32) 15137) /* FIX(1.847759065) */ 73#define FIX_2_172734803 ((INT32) 17799) /* FIX(2.172734803) */ 74#define FIX_2_562915447 ((INT32) 20995) /* FIX(2.562915447) */ 75#define FIX_3_624509785 ((INT32) 29692) /* FIX(3.624509785) */ 76#else 77#define FIX_0_211164243 FIX(0.211164243) 78#define FIX_0_509795579 FIX(0.509795579) 79#define FIX_0_601344887 FIX(0.601344887) 80#define FIX_0_720959822 FIX(0.720959822) 81#define FIX_0_765366865 FIX(0.765366865) 82#define FIX_0_850430095 FIX(0.850430095) 83#define FIX_0_899976223 FIX(0.899976223) 84#define FIX_1_061594337 FIX(1.061594337) 85#define FIX_1_272758580 FIX(1.272758580) 86#define FIX_1_451774981 FIX(1.451774981) 87#define FIX_1_847759065 FIX(1.847759065) 88#define FIX_2_172734803 FIX(2.172734803) 89#define FIX_2_562915447 FIX(2.562915447) 90#define FIX_3_624509785 FIX(3.624509785) 91#endif 92 93 94/* Multiply an INT32 variable by an INT32 constant to yield an INT32 result. 95 * For 8-bit samples with the recommended scaling, all the variable 96 * and constant values involved are no more than 16 bits wide, so a 97 * 16x16->32 bit multiply can be used instead of a full 32x32 multiply. 98 * For 12-bit samples, a full 32-bit multiplication will be needed. 99 */ 100 101#if BITS_IN_JSAMPLE == 8 102#define MULTIPLY(var,const) MULTIPLY16C16(var,const) 103#else 104#define MULTIPLY(var,const) ((var) * (const)) 105#endif 106 107 108/* Dequantize a coefficient by multiplying it by the multiplier-table 109 * entry; produce an int result. In this module, both inputs and result 110 * are 16 bits or less, so either int or short multiply will work. 111 */ 112 113#define DEQUANTIZE(coef,quantval) (((ISLOW_MULT_TYPE) (coef)) * (quantval)) 114 115 116/* 117 * Perform dequantization and inverse DCT on one block of coefficients, 118 * producing a reduced-size 4x4 output block. 119 */ 120 121GLOBAL(void) 122jpeg_idct_4x4 (j_decompress_ptr cinfo, jpeg_component_info * compptr, 123 JCOEFPTR coef_block, 124 JSAMPARRAY output_buf, JDIMENSION output_col) 125{ 126 INT32 tmp0, tmp2, tmp10, tmp12; 127 INT32 z1, z2, z3, z4; 128 JCOEFPTR inptr; 129 ISLOW_MULT_TYPE * quantptr; 130 int * wsptr; 131 JSAMPROW outptr; 132 JSAMPLE *range_limit = IDCT_range_limit(cinfo); 133 int ctr; 134 int workspace[DCTSIZE*4]; /* buffers data between passes */ 135 SHIFT_TEMPS 136 137 /* Pass 1: process columns from input, store into work array. */ 138 139 inptr = coef_block; 140 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table; 141 wsptr = workspace; 142 for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) { 143 /* Don't bother to process column 4, because second pass won't use it */ 144 if (ctr == DCTSIZE-4) 145 continue; 146 if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 && 147 inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*5] == 0 && 148 inptr[DCTSIZE*6] == 0 && inptr[DCTSIZE*7] == 0) { 149 /* AC terms all zero; we need not examine term 4 for 4x4 output */ 150 int dcval = DEQUANTIZE(inptr[DCTSIZE*0], 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 <<= (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((INT32) 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 = ((INT32) wsptr[0]) << (CONST_BITS+1); 225 226 tmp2 = MULTIPLY((INT32) wsptr[2], FIX_1_847759065) 227 + MULTIPLY((INT32) wsptr[6], - FIX_0_765366865); 228 229 tmp10 = tmp0 + tmp2; 230 tmp12 = tmp0 - tmp2; 231 232 /* Odd part */ 233 234 z1 = (INT32) wsptr[7]; 235 z2 = (INT32) wsptr[5]; 236 z3 = (INT32) wsptr[3]; 237 z4 = (INT32) 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 274GLOBAL(void) 275jpeg_idct_2x2 (j_decompress_ptr cinfo, jpeg_component_info * compptr, 276 JCOEFPTR coef_block, 277 JSAMPARRAY output_buf, JDIMENSION output_col) 278{ 279 INT32 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 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << 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 = 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 = ((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 382GLOBAL(void) 383jpeg_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