1/* 2 * jidctred.c 3 * 4 * Copyright (C) 1994-1998, 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 inverse-DCT routines that produce reduced-size output: 9 * either 4x4, 2x2, or 1x1 pixels from an 8x8 DCT block. 10 * 11 * The implementation is based on the Loeffler, Ligtenberg and Moschytz (LL&M) 12 * algorithm used in jidctint.c. We simply replace each 8-to-8 1-D IDCT step 13 * with an 8-to-4 step that produces the four averages of two adjacent outputs 14 * (or an 8-to-2 step producing two averages of four outputs, for 2x2 output). 15 * These steps were derived by computing the corresponding values at the end 16 * of the normal LL&M code, then simplifying as much as possible. 17 * 18 * 1x1 is trivial: just take the DC coefficient divided by 8. 19 * 20 * See jidctint.c for additional comments. 21 */ 22 23#define JPEG_INTERNALS 24#include "jinclude.h" 25#include "jpeglib.h" 26#include "jdct.h" /* Private declarations for DCT subsystem */ 27 28#ifdef IDCT_SCALING_SUPPORTED 29 30 31/* 32 * This module is specialized to the case DCTSIZE = 8. 33 */ 34 35#if DCTSIZE != 8 36 Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */ 37#endif 38 39 40/* Scaling is the same as in jidctint.c. */ 41 42#if BITS_IN_JSAMPLE == 8 43#define CONST_BITS 13 44#define PASS1_BITS 2 45#else 46#define CONST_BITS 13 47#define PASS1_BITS 1 /* lose a little precision to avoid overflow */ 48#endif 49 50/* Some C compilers fail to reduce "FIX(constant)" at compile time, thus 51 * causing a lot of useless floating-point operations at run time. 52 * To get around this we use the following pre-calculated constants. 53 * If you change CONST_BITS you may want to add appropriate values. 54 * (With a reasonable C compiler, you can just rely on the FIX() macro...) 55 */ 56 57#if CONST_BITS == 13 58#define FIX_0_211164243 ((INT32) 1730) /* FIX(0.211164243) */ 59#define FIX_0_509795579 ((INT32) 4176) /* FIX(0.509795579) */ 60#define FIX_0_601344887 ((INT32) 4926) /* FIX(0.601344887) */ 61#define FIX_0_720959822 ((INT32) 5906) /* FIX(0.720959822) */ 62#define FIX_0_765366865 ((INT32) 6270) /* FIX(0.765366865) */ 63#define FIX_0_850430095 ((INT32) 6967) /* FIX(0.850430095) */ 64#define FIX_0_899976223 ((INT32) 7373) /* FIX(0.899976223) */ 65#define FIX_1_061594337 ((INT32) 8697) /* FIX(1.061594337) */ 66#define FIX_1_272758580 ((INT32) 10426) /* FIX(1.272758580) */ 67#define FIX_1_451774981 ((INT32) 11893) /* FIX(1.451774981) */ 68#define FIX_1_847759065 ((INT32) 15137) /* FIX(1.847759065) */ 69#define FIX_2_172734803 ((INT32) 17799) /* FIX(2.172734803) */ 70#define FIX_2_562915447 ((INT32) 20995) /* FIX(2.562915447) */ 71#define FIX_3_624509785 ((INT32) 29692) /* FIX(3.624509785) */ 72#else 73#define FIX_0_211164243 FIX(0.211164243) 74#define FIX_0_509795579 FIX(0.509795579) 75#define FIX_0_601344887 FIX(0.601344887) 76#define FIX_0_720959822 FIX(0.720959822) 77#define FIX_0_765366865 FIX(0.765366865) 78#define FIX_0_850430095 FIX(0.850430095) 79#define FIX_0_899976223 FIX(0.899976223) 80#define FIX_1_061594337 FIX(1.061594337) 81#define FIX_1_272758580 FIX(1.272758580) 82#define FIX_1_451774981 FIX(1.451774981) 83#define FIX_1_847759065 FIX(1.847759065) 84#define FIX_2_172734803 FIX(2.172734803) 85#define FIX_2_562915447 FIX(2.562915447) 86#define FIX_3_624509785 FIX(3.624509785) 87#endif 88 89 90/* Multiply an INT32 variable by an INT32 constant to yield an INT32 result. 91 * For 8-bit samples with the recommended scaling, all the variable 92 * and constant values involved are no more than 16 bits wide, so a 93 * 16x16->32 bit multiply can be used instead of a full 32x32 multiply. 94 * For 12-bit samples, a full 32-bit multiplication will be needed. 95 */ 96 97#if BITS_IN_JSAMPLE == 8 98#define MULTIPLY(var,const) MULTIPLY16C16(var,const) 99#else 100#define MULTIPLY(var,const) ((var) * (const)) 101#endif 102 103 104/* Dequantize a coefficient by multiplying it by the multiplier-table 105 * entry; produce an int result. In this module, both inputs and result 106 * are 16 bits or less, so either int or short multiply will work. 107 */ 108 109#define DEQUANTIZE(coef,quantval) (((ISLOW_MULT_TYPE) (coef)) * (quantval)) 110 111 112/* 113 * Perform dequantization and inverse DCT on one block of coefficients, 114 * producing a reduced-size 4x4 output block. 115 */ 116 117GLOBAL(void) 118jpeg_idct_4x4 (j_decompress_ptr cinfo, jpeg_component_info * compptr, 119 JCOEFPTR coef_block, 120 JSAMPARRAY output_buf, JDIMENSION output_col) 121{ 122 INT32 tmp0, tmp2, tmp10, tmp12; 123 INT32 z1, z2, z3, z4; 124 JCOEFPTR inptr; 125 ISLOW_MULT_TYPE * quantptr; 126 int * wsptr; 127 JSAMPROW outptr; 128 JSAMPLE *range_limit = IDCT_range_limit(cinfo); 129 int ctr; 130 int workspace[DCTSIZE*4]; /* buffers data between passes */ 131 SHIFT_TEMPS 132 133 /* Pass 1: process columns from input, store into work array. */ 134 135 inptr = coef_block; 136 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table; 137 wsptr = workspace; 138 for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) { 139 /* Don't bother to process column 4, because second pass won't use it */ 140 if (ctr == DCTSIZE-4) 141 continue; 142 if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 && 143 inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*5] == 0 && 144 inptr[DCTSIZE*6] == 0 && inptr[DCTSIZE*7] == 0) { 145 /* AC terms all zero; we need not examine term 4 for 4x4 output */ 146 int dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << PASS1_BITS; 147 148 wsptr[DCTSIZE*0] = dcval; 149 wsptr[DCTSIZE*1] = dcval; 150 wsptr[DCTSIZE*2] = dcval; 151 wsptr[DCTSIZE*3] = dcval; 152 153 continue; 154 } 155 156 /* Even part */ 157 158 tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]); 159 tmp0 <<= (CONST_BITS+1); 160 161 z2 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]); 162 z3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]); 163 164 tmp2 = MULTIPLY(z2, FIX_1_847759065) + MULTIPLY(z3, - FIX_0_765366865); 165 166 tmp10 = tmp0 + tmp2; 167 tmp12 = tmp0 - tmp2; 168 169 /* Odd part */ 170 171 z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]); 172 z2 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]); 173 z3 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]); 174 z4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]); 175 176 tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */ 177 + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */ 178 + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */ 179 + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */ 180 181 tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */ 182 + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */ 183 + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */ 184 + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */ 185 186 /* Final output stage */ 187 188 wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp2, CONST_BITS-PASS1_BITS+1); 189 wsptr[DCTSIZE*3] = (int) DESCALE(tmp10 - tmp2, CONST_BITS-PASS1_BITS+1); 190 wsptr[DCTSIZE*1] = (int) DESCALE(tmp12 + tmp0, CONST_BITS-PASS1_BITS+1); 191 wsptr[DCTSIZE*2] = (int) DESCALE(tmp12 - tmp0, CONST_BITS-PASS1_BITS+1); 192 } 193 194 /* Pass 2: process 4 rows from work array, store into output array. */ 195 196 wsptr = workspace; 197 for (ctr = 0; ctr < 4; ctr++) { 198 outptr = output_buf[ctr] + output_col; 199 /* It's not clear whether a zero row test is worthwhile here ... */ 200 201#ifndef NO_ZERO_ROW_TEST 202 if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 && 203 wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) { 204 /* AC terms all zero */ 205 JSAMPLE dcval = range_limit[(int) DESCALE((INT32) wsptr[0], PASS1_BITS+3) 206 & RANGE_MASK]; 207 208 outptr[0] = dcval; 209 outptr[1] = dcval; 210 outptr[2] = dcval; 211 outptr[3] = dcval; 212 213 wsptr += DCTSIZE; /* advance pointer to next row */ 214 continue; 215 } 216#endif 217 218 /* Even part */ 219 220 tmp0 = ((INT32) wsptr[0]) << (CONST_BITS+1); 221 222 tmp2 = MULTIPLY((INT32) wsptr[2], FIX_1_847759065) 223 + MULTIPLY((INT32) wsptr[6], - FIX_0_765366865); 224 225 tmp10 = tmp0 + tmp2; 226 tmp12 = tmp0 - tmp2; 227 228 /* Odd part */ 229 230 z1 = (INT32) wsptr[7]; 231 z2 = (INT32) wsptr[5]; 232 z3 = (INT32) wsptr[3]; 233 z4 = (INT32) wsptr[1]; 234 235 tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */ 236 + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */ 237 + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */ 238 + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */ 239 240 tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */ 241 + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */ 242 + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */ 243 + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */ 244 245 /* Final output stage */ 246 247 outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp2, 248 CONST_BITS+PASS1_BITS+3+1) 249 & RANGE_MASK]; 250 outptr[3] = range_limit[(int) DESCALE(tmp10 - tmp2, 251 CONST_BITS+PASS1_BITS+3+1) 252 & RANGE_MASK]; 253 outptr[1] = range_limit[(int) DESCALE(tmp12 + tmp0, 254 CONST_BITS+PASS1_BITS+3+1) 255 & RANGE_MASK]; 256 outptr[2] = range_limit[(int) DESCALE(tmp12 - tmp0, 257 CONST_BITS+PASS1_BITS+3+1) 258 & RANGE_MASK]; 259 260 wsptr += DCTSIZE; /* advance pointer to next row */ 261 } 262} 263 264 265/* 266 * Perform dequantization and inverse DCT on one block of coefficients, 267 * producing a reduced-size 2x2 output block. 268 */ 269 270GLOBAL(void) 271jpeg_idct_2x2 (j_decompress_ptr cinfo, jpeg_component_info * compptr, 272 JCOEFPTR coef_block, 273 JSAMPARRAY output_buf, JDIMENSION output_col) 274{ 275 INT32 tmp0, tmp10, z1; 276 JCOEFPTR inptr; 277 ISLOW_MULT_TYPE * quantptr; 278 int * wsptr; 279 JSAMPROW outptr; 280 JSAMPLE *range_limit = IDCT_range_limit(cinfo); 281 int ctr; 282 int workspace[DCTSIZE*2]; /* buffers data between passes */ 283 SHIFT_TEMPS 284 285 /* Pass 1: process columns from input, store into work array. */ 286 287 inptr = coef_block; 288 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table; 289 wsptr = workspace; 290 for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) { 291 /* Don't bother to process columns 2,4,6 */ 292 if (ctr == DCTSIZE-2 || ctr == DCTSIZE-4 || ctr == DCTSIZE-6) 293 continue; 294 if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*3] == 0 && 295 inptr[DCTSIZE*5] == 0 && inptr[DCTSIZE*7] == 0) { 296 /* AC terms all zero; we need not examine terms 2,4,6 for 2x2 output */ 297 int dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << PASS1_BITS; 298 299 wsptr[DCTSIZE*0] = dcval; 300 wsptr[DCTSIZE*1] = dcval; 301 302 continue; 303 } 304 305 /* Even part */ 306 307 z1 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]); 308 tmp10 = z1 << (CONST_BITS+2); 309 310 /* Odd part */ 311 312 z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]); 313 tmp0 = MULTIPLY(z1, - FIX_0_720959822); /* sqrt(2) * (c7-c5+c3-c1) */ 314 z1 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]); 315 tmp0 += MULTIPLY(z1, FIX_0_850430095); /* sqrt(2) * (-c1+c3+c5+c7) */ 316 z1 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]); 317 tmp0 += MULTIPLY(z1, - FIX_1_272758580); /* sqrt(2) * (-c1+c3-c5-c7) */ 318 z1 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]); 319 tmp0 += MULTIPLY(z1, FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */ 320 321 /* Final output stage */ 322 323 wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp0, CONST_BITS-PASS1_BITS+2); 324 wsptr[DCTSIZE*1] = (int) DESCALE(tmp10 - tmp0, CONST_BITS-PASS1_BITS+2); 325 } 326 327 /* Pass 2: process 2 rows from work array, store into output array. */ 328 329 wsptr = workspace; 330 for (ctr = 0; ctr < 2; ctr++) { 331 outptr = output_buf[ctr] + output_col; 332 /* It's not clear whether a zero row test is worthwhile here ... */ 333 334#ifndef NO_ZERO_ROW_TEST 335 if (wsptr[1] == 0 && wsptr[3] == 0 && wsptr[5] == 0 && wsptr[7] == 0) { 336 /* AC terms all zero */ 337 JSAMPLE dcval = range_limit[(int) DESCALE((INT32) wsptr[0], PASS1_BITS+3) 338 & RANGE_MASK]; 339 340 outptr[0] = dcval; 341 outptr[1] = dcval; 342 343 wsptr += DCTSIZE; /* advance pointer to next row */ 344 continue; 345 } 346#endif 347 348 /* Even part */ 349 350 tmp10 = ((INT32) wsptr[0]) << (CONST_BITS+2); 351 352 /* Odd part */ 353 354 tmp0 = MULTIPLY((INT32) wsptr[7], - FIX_0_720959822) /* sqrt(2) * (c7-c5+c3-c1) */ 355 + MULTIPLY((INT32) wsptr[5], FIX_0_850430095) /* sqrt(2) * (-c1+c3+c5+c7) */ 356 + MULTIPLY((INT32) wsptr[3], - FIX_1_272758580) /* sqrt(2) * (-c1+c3-c5-c7) */ 357 + MULTIPLY((INT32) wsptr[1], FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */ 358 359 /* Final output stage */ 360 361 outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp0, 362 CONST_BITS+PASS1_BITS+3+2) 363 & RANGE_MASK]; 364 outptr[1] = range_limit[(int) DESCALE(tmp10 - tmp0, 365 CONST_BITS+PASS1_BITS+3+2) 366 & RANGE_MASK]; 367 368 wsptr += DCTSIZE; /* advance pointer to next row */ 369 } 370} 371 372 373/* 374 * Perform dequantization and inverse DCT on one block of coefficients, 375 * producing a reduced-size 1x1 output block. 376 */ 377 378GLOBAL(void) 379jpeg_idct_1x1 (j_decompress_ptr cinfo, jpeg_component_info * compptr, 380 JCOEFPTR coef_block, 381 JSAMPARRAY output_buf, JDIMENSION output_col) 382{ 383 int dcval; 384 ISLOW_MULT_TYPE * quantptr; 385 JSAMPLE *range_limit = IDCT_range_limit(cinfo); 386 SHIFT_TEMPS 387 388 /* We hardly need an inverse DCT routine for this: just take the 389 * average pixel value, which is one-eighth of the DC coefficient. 390 */ 391 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table; 392 dcval = DEQUANTIZE(coef_block[0], quantptr[0]); 393 dcval = (int) DESCALE((INT32) dcval, 3); 394 395 output_buf[0][output_col] = range_limit[dcval & RANGE_MASK]; 396} 397 398#endif /* IDCT_SCALING_SUPPORTED */ 399