src/jpeg/jidctred.c

   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  ((JPEG_INT32)  1730)   /* FIX(0.211164243) */
  59 #define FIX_0_509795579  ((JPEG_INT32)  4176)   /* FIX(0.509795579) */
  60 #define FIX_0_601344887  ((JPEG_INT32)  4926)   /* FIX(0.601344887) */
  61 #define FIX_0_720959822  ((JPEG_INT32)  5906)   /* FIX(0.720959822) */
  62 #define FIX_0_765366865  ((JPEG_INT32)  6270)   /* FIX(0.765366865) */
  63 #define FIX_0_850430095  ((JPEG_INT32)  6967)   /* FIX(0.850430095) */
  64 #define FIX_0_899976223  ((JPEG_INT32)  7373)   /* FIX(0.899976223) */
  65 #define FIX_1_061594337  ((JPEG_INT32)  8697)   /* FIX(1.061594337) */
  66 #define FIX_1_272758580  ((JPEG_INT32)  10426)  /* FIX(1.272758580) */
  67 #define FIX_1_451774981  ((JPEG_INT32)  11893)  /* FIX(1.451774981) */
  68 #define FIX_1_847759065  ((JPEG_INT32)  15137)  /* FIX(1.847759065) */
  69 #define FIX_2_172734803  ((JPEG_INT32)  17799)  /* FIX(2.172734803) */
  70 #define FIX_2_562915447  ((JPEG_INT32)  20995)  /* FIX(2.562915447) */
  71 #define FIX_3_624509785  ((JPEG_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 {
 122   JPEG_INT32 tmp0, tmp2, tmp10, tmp12;
 123   JPEG_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((JPEG_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 = ((JPEG_INT32) wsptr[0]) << (CONST_BITS+1);
 221
 222     tmp2 = MULTIPLY((JPEG_INT32) wsptr[2], FIX_1_847759065)
 223          + MULTIPLY((JPEG_INT32) wsptr[6], - FIX_0_765366865);
 224
 225     tmp10 = tmp0 + tmp2;
 226     tmp12 = tmp0 - tmp2;
 227
 228     /* Odd part */
 229
 230     z1 = (JPEG_INT32) wsptr[7];
 231     z2 = (JPEG_INT32) wsptr[5];
 232     z3 = (JPEG_INT32) wsptr[3];
 233     z4 = (JPEG_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
 270 GLOBAL(void)
 271 jpeg_idct_2x2 (j_decompress_ptr cinfo, jpeg_component_info * compptr,
 272                JCOEFPTR coef_block,
 273                JSAMPARRAY output_buf, JDIMENSION output_col)
 274 {
 275   JPEG_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((JPEG_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 = ((JPEG_INT32) wsptr[0]) << (CONST_BITS+2);
 351
 352     /* Odd part */
 353
 354     tmp0 = MULTIPLY((JPEG_INT32) wsptr[7], - FIX_0_720959822) /* sqrt(2) * (c7-c5+c3-c1) */
 355          + MULTIPLY((JPEG_INT32) wsptr[5], FIX_0_850430095) /* sqrt(2) * (-c1+c3+c5+c7) */
 356          + MULTIPLY((JPEG_INT32) wsptr[3], - FIX_1_272758580) /* sqrt(2) * (-c1+c3-c5-c7) */
 357          + MULTIPLY((JPEG_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
 378 GLOBAL(void)
 379 jpeg_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((JPEG_INT32) dcval, 3);
 394
 395   output_buf[0][output_col] = range_limit[dcval & RANGE_MASK];
 396 }
 397
 398 #endif /* IDCT_SCALING_SUPPORTED */