jidctred.cpp (15072B)
1 /* 2 * jidctred.c 3 * 4 * Copyright (C) 1994, 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 8 x8 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 */ 116 117 GLOBAL void 118 jpeg_idct_4x4( j_decompress_ptr cinfo, jpeg_component_info * compptr, 119 JCOEFPTR coef_block, 120 JSAMPARRAY output_buf, JDIMENSION output_col ) { 121 INT32 tmp0, tmp2, tmp10, tmp12; 122 INT32 z1, z2, z3, z4; 123 JCOEFPTR inptr; 124 ISLOW_MULT_TYPE * quantptr; 125 int * wsptr; 126 JSAMPROW outptr; 127 JSAMPLE * range_limit = IDCT_range_limit( cinfo ); 128 int ctr; 129 int workspace[DCTSIZE * 4];/* buffers data between passes */ 130 SHIFT_TEMPS 131 132 /* Pass 1: process columns from input, store into work array. */ 133 134 inptr = coef_block; 135 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table; 136 wsptr = workspace; 137 for ( ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr-- ) { 138 /* Don't bother to process column 4, because second pass won't use it */ 139 if ( ctr == DCTSIZE - 4 ) { 140 continue; 141 } 142 if ( ( inptr[DCTSIZE * 1] | inptr[DCTSIZE * 2] | inptr[DCTSIZE * 3] | 143 inptr[DCTSIZE * 5] | inptr[DCTSIZE * 6] | inptr[DCTSIZE * 7] ) == 0 ) { 144 /* AC terms all zero; we need not examine term 4 for 4x4 output */ 145 int dcval = DEQUANTIZE( inptr[DCTSIZE * 0], quantptr[DCTSIZE * 0] ) << PASS1_BITS; 146 147 wsptr[DCTSIZE * 0] = dcval; 148 wsptr[DCTSIZE * 1] = dcval; 149 wsptr[DCTSIZE * 2] = dcval; 150 wsptr[DCTSIZE * 3] = dcval; 151 152 continue; 153 } 154 155 /* Even part */ 156 157 tmp0 = DEQUANTIZE( inptr[DCTSIZE * 0], quantptr[DCTSIZE * 0] ); 158 tmp0 <<= ( CONST_BITS + 1 ); 159 160 z2 = DEQUANTIZE( inptr[DCTSIZE * 2], quantptr[DCTSIZE * 2] ); 161 z3 = DEQUANTIZE( inptr[DCTSIZE * 6], quantptr[DCTSIZE * 6] ); 162 163 tmp2 = MULTIPLY( z2, FIX_1_847759065 ) + MULTIPLY( z3, -FIX_0_765366865 ); 164 165 tmp10 = tmp0 + tmp2; 166 tmp12 = tmp0 - tmp2; 167 168 /* Odd part */ 169 170 z1 = DEQUANTIZE( inptr[DCTSIZE * 7], quantptr[DCTSIZE * 7] ); 171 z2 = DEQUANTIZE( inptr[DCTSIZE * 5], quantptr[DCTSIZE * 5] ); 172 z3 = DEQUANTIZE( inptr[DCTSIZE * 3], quantptr[DCTSIZE * 3] ); 173 z4 = DEQUANTIZE( inptr[DCTSIZE * 1], quantptr[DCTSIZE * 1] ); 174 175 tmp0 = MULTIPLY( z1, -FIX_0_211164243 )/* sqrt(2) * (c3-c1) */ 176 + MULTIPLY( z2, FIX_1_451774981 )/* sqrt(2) * (c3+c7) */ 177 + MULTIPLY( z3, -FIX_2_172734803 )/* sqrt(2) * (-c1-c5) */ 178 + MULTIPLY( z4, FIX_1_061594337 );/* sqrt(2) * (c5+c7) */ 179 180 tmp2 = MULTIPLY( z1, -FIX_0_509795579 )/* sqrt(2) * (c7-c5) */ 181 + MULTIPLY( z2, -FIX_0_601344887 )/* sqrt(2) * (c5-c1) */ 182 + MULTIPLY( z3, FIX_0_899976223 )/* sqrt(2) * (c3-c7) */ 183 + MULTIPLY( z4, FIX_2_562915447 );/* sqrt(2) * (c1+c3) */ 184 185 /* Final output stage */ 186 187 wsptr[DCTSIZE * 0] = (int) DESCALE( tmp10 + tmp2, CONST_BITS - PASS1_BITS + 1 ); 188 wsptr[DCTSIZE * 3] = (int) DESCALE( tmp10 - tmp2, CONST_BITS - PASS1_BITS + 1 ); 189 wsptr[DCTSIZE * 1] = (int) DESCALE( tmp12 + tmp0, CONST_BITS - PASS1_BITS + 1 ); 190 wsptr[DCTSIZE * 2] = (int) DESCALE( tmp12 - tmp0, CONST_BITS - PASS1_BITS + 1 ); 191 } 192 193 /* Pass 2: process 4 rows from work array, store into output array. */ 194 195 wsptr = workspace; 196 for ( ctr = 0; ctr < 4; ctr++ ) { 197 outptr = output_buf[ctr] + output_col; 198 /* It's not clear whether a zero row test is worthwhile here ... */ 199 200 #ifndef NO_ZERO_ROW_TEST 201 if ( ( wsptr[1] | wsptr[2] | wsptr[3] | wsptr[5] | wsptr[6] | 202 wsptr[7] ) == 0 ) { 203 /* AC terms all zero */ 204 JSAMPLE dcval = range_limit[(int) DESCALE( (INT32) wsptr[0], PASS1_BITS + 3 ) 205 & RANGE_MASK]; 206 207 outptr[0] = dcval; 208 outptr[1] = dcval; 209 outptr[2] = dcval; 210 outptr[3] = dcval; 211 212 wsptr += DCTSIZE;/* advance pointer to next row */ 213 continue; 214 } 215 #endif 216 217 /* Even part */ 218 219 tmp0 = ( (INT32) wsptr[0] ) << ( CONST_BITS + 1 ); 220 221 tmp2 = MULTIPLY( (INT32) wsptr[2], FIX_1_847759065 ) 222 + MULTIPLY( (INT32) wsptr[6], -FIX_0_765366865 ); 223 224 tmp10 = tmp0 + tmp2; 225 tmp12 = tmp0 - tmp2; 226 227 /* Odd part */ 228 229 z1 = (INT32) wsptr[7]; 230 z2 = (INT32) wsptr[5]; 231 z3 = (INT32) wsptr[3]; 232 z4 = (INT32) wsptr[1]; 233 234 tmp0 = MULTIPLY( z1, -FIX_0_211164243 )/* sqrt(2) * (c3-c1) */ 235 + MULTIPLY( z2, FIX_1_451774981 )/* sqrt(2) * (c3+c7) */ 236 + MULTIPLY( z3, -FIX_2_172734803 )/* sqrt(2) * (-c1-c5) */ 237 + MULTIPLY( z4, FIX_1_061594337 );/* sqrt(2) * (c5+c7) */ 238 239 tmp2 = MULTIPLY( z1, -FIX_0_509795579 )/* sqrt(2) * (c7-c5) */ 240 + MULTIPLY( z2, -FIX_0_601344887 )/* sqrt(2) * (c5-c1) */ 241 + MULTIPLY( z3, FIX_0_899976223 )/* sqrt(2) * (c3-c7) */ 242 + MULTIPLY( z4, FIX_2_562915447 );/* sqrt(2) * (c1+c3) */ 243 244 /* Final output stage */ 245 246 outptr[0] = range_limit[(int) DESCALE( tmp10 + tmp2, 247 CONST_BITS + PASS1_BITS + 3 + 1 ) 248 & RANGE_MASK]; 249 outptr[3] = range_limit[(int) DESCALE( tmp10 - tmp2, 250 CONST_BITS + PASS1_BITS + 3 + 1 ) 251 & RANGE_MASK]; 252 outptr[1] = range_limit[(int) DESCALE( tmp12 + tmp0, 253 CONST_BITS + PASS1_BITS + 3 + 1 ) 254 & RANGE_MASK]; 255 outptr[2] = range_limit[(int) DESCALE( tmp12 - tmp0, 256 CONST_BITS + PASS1_BITS + 3 + 1 ) 257 & RANGE_MASK]; 258 259 wsptr += DCTSIZE; /* advance pointer to next row */ 260 } 261 } 262 263 264 /* 265 * Perform dequantization and inverse DCT on one block of coefficients, 266 * producing a reduced-size 2x2 output block. 267 */ 268 269 GLOBAL void 270 jpeg_idct_2x2( j_decompress_ptr cinfo, jpeg_component_info * compptr, 271 JCOEFPTR coef_block, 272 JSAMPARRAY output_buf, JDIMENSION output_col ) { 273 INT32 tmp0, tmp10, z1; 274 JCOEFPTR inptr; 275 ISLOW_MULT_TYPE * quantptr; 276 int * wsptr; 277 JSAMPROW outptr; 278 JSAMPLE * range_limit = IDCT_range_limit( cinfo ); 279 int ctr; 280 int workspace[DCTSIZE * 2];/* buffers data between passes */ 281 SHIFT_TEMPS 282 283 /* Pass 1: process columns from input, store into work array. */ 284 285 inptr = coef_block; 286 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table; 287 wsptr = workspace; 288 for ( ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr-- ) { 289 /* Don't bother to process columns 2,4,6 */ 290 if ( ( ctr == DCTSIZE - 2 ) || ( ctr == DCTSIZE - 4 ) || ( ctr == DCTSIZE - 6 ) ) { 291 continue; 292 } 293 if ( ( inptr[DCTSIZE * 1] | inptr[DCTSIZE * 3] | 294 inptr[DCTSIZE * 5] | inptr[DCTSIZE * 7] ) == 0 ) { 295 /* AC terms all zero; we need not examine terms 2,4,6 for 2x2 output */ 296 int dcval = DEQUANTIZE( inptr[DCTSIZE * 0], quantptr[DCTSIZE * 0] ) << PASS1_BITS; 297 298 wsptr[DCTSIZE * 0] = dcval; 299 wsptr[DCTSIZE * 1] = dcval; 300 301 continue; 302 } 303 304 /* Even part */ 305 306 z1 = DEQUANTIZE( inptr[DCTSIZE * 0], quantptr[DCTSIZE * 0] ); 307 tmp10 = z1 << ( CONST_BITS + 2 ); 308 309 /* Odd part */ 310 311 z1 = DEQUANTIZE( inptr[DCTSIZE * 7], quantptr[DCTSIZE * 7] ); 312 tmp0 = MULTIPLY( z1, -FIX_0_720959822 );/* sqrt(2) * (c7-c5+c3-c1) */ 313 z1 = DEQUANTIZE( inptr[DCTSIZE * 5], quantptr[DCTSIZE * 5] ); 314 tmp0 += MULTIPLY( z1, FIX_0_850430095 );/* sqrt(2) * (-c1+c3+c5+c7) */ 315 z1 = DEQUANTIZE( inptr[DCTSIZE * 3], quantptr[DCTSIZE * 3] ); 316 tmp0 += MULTIPLY( z1, -FIX_1_272758580 );/* sqrt(2) * (-c1+c3-c5-c7) */ 317 z1 = DEQUANTIZE( inptr[DCTSIZE * 1], quantptr[DCTSIZE * 1] ); 318 tmp0 += MULTIPLY( z1, FIX_3_624509785 );/* sqrt(2) * (c1+c3+c5+c7) */ 319 320 /* Final output stage */ 321 322 wsptr[DCTSIZE * 0] = (int) DESCALE( tmp10 + tmp0, CONST_BITS - PASS1_BITS + 2 ); 323 wsptr[DCTSIZE * 1] = (int) DESCALE( tmp10 - tmp0, CONST_BITS - PASS1_BITS + 2 ); 324 } 325 326 /* Pass 2: process 2 rows from work array, store into output array. */ 327 328 wsptr = workspace; 329 for ( ctr = 0; ctr < 2; ctr++ ) { 330 outptr = output_buf[ctr] + output_col; 331 /* It's not clear whether a zero row test is worthwhile here ... */ 332 333 #ifndef NO_ZERO_ROW_TEST 334 if ( ( wsptr[1] | wsptr[3] | wsptr[5] | wsptr[7] ) == 0 ) { 335 /* AC terms all zero */ 336 JSAMPLE dcval = range_limit[(int) DESCALE( (INT32) wsptr[0], PASS1_BITS + 3 ) 337 & RANGE_MASK]; 338 339 outptr[0] = dcval; 340 outptr[1] = dcval; 341 342 wsptr += DCTSIZE;/* advance pointer to next row */ 343 continue; 344 } 345 #endif 346 347 /* Even part */ 348 349 tmp10 = ( (INT32) wsptr[0] ) << ( CONST_BITS + 2 ); 350 351 /* Odd part */ 352 353 tmp0 = MULTIPLY( (INT32) wsptr[7], -FIX_0_720959822 )/* sqrt(2) * (c7-c5+c3-c1) */ 354 + MULTIPLY( (INT32) wsptr[5], FIX_0_850430095 )/* sqrt(2) * (-c1+c3+c5+c7) */ 355 + MULTIPLY( (INT32) wsptr[3], -FIX_1_272758580 )/* sqrt(2) * (-c1+c3-c5-c7) */ 356 + MULTIPLY( (INT32) wsptr[1], FIX_3_624509785 );/* sqrt(2) * (c1+c3+c5+c7) */ 357 358 /* Final output stage */ 359 360 outptr[0] = range_limit[(int) DESCALE( tmp10 + tmp0, 361 CONST_BITS + PASS1_BITS + 3 + 2 ) 362 & RANGE_MASK]; 363 outptr[1] = range_limit[(int) DESCALE( tmp10 - tmp0, 364 CONST_BITS + PASS1_BITS + 3 + 2 ) 365 & RANGE_MASK]; 366 367 wsptr += DCTSIZE; /* advance pointer to next row */ 368 } 369 } 370 371 372 /* 373 * Perform dequantization and inverse DCT on one block of coefficients, 374 * producing a reduced-size 1x1 output block. 375 */ 376 377 GLOBAL void 378 jpeg_idct_1x1( j_decompress_ptr cinfo, jpeg_component_info * compptr, 379 JCOEFPTR coef_block, 380 JSAMPARRAY output_buf, JDIMENSION output_col ) { 381 int dcval; 382 ISLOW_MULT_TYPE * quantptr; 383 JSAMPLE * range_limit = IDCT_range_limit( cinfo ); 384 SHIFT_TEMPS 385 386 /* We hardly need an inverse DCT routine for this: just take the 387 * average pixel value, which is one-eighth of the DC coefficient. 388 */ 389 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table; 390 dcval = DEQUANTIZE( coef_block[0], quantptr[0] ); 391 dcval = (int) DESCALE( (INT32) dcval, 3 ); 392 393 output_buf[0][output_col] = range_limit[dcval & RANGE_MASK]; 394 } 395 396 #endif /* IDCT_SCALING_SUPPORTED */