compiler/libjpeg/main/jidctred.c

   1 /*
   2     $Id$
   3 */
   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
 121 JGLOBAL(void)
 122 jpeg_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
 274 JGLOBAL(void)
 275 jpeg_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
 382 JGLOBAL(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 */