media/libjpeg/jidctred.c

   1 /*
   2  * jidctred.c
   3  *
   4  * This file was part of the Independent JPEG Group's software:
   5  * Copyright (C) 1994-1998, Thomas G. Lane.
   6  * libjpeg-turbo Modifications:
   7  * Copyright (C) 2015, D. R. Commander.
   8  * For conditions of distribution and use, see the accompanying README.ijg
   9  * file.
  10  *
  11  * This file contains inverse-DCT routines that produce reduced-size output:
  12  * either 4x4, 2x2, or 1x1 pixels from an 8x8 DCT block.
  13  *
  14  * The implementation is based on the Loeffler, Ligtenberg and Moschytz (LL&M)
  15  * algorithm used in jidctint.c.  We simply replace each 8-to-8 1-D IDCT step
  16  * with an 8-to-4 step that produces the four averages of two adjacent outputs
  17  * (or an 8-to-2 step producing two averages of four outputs, for 2x2 output).
  18  * These steps were derived by computing the corresponding values at the end
  19  * of the normal LL&M code, then simplifying as much as possible.
  20  *
  21  * 1x1 is trivial: just take the DC coefficient divided by 8.
  22  *
  23  * See jidctint.c for additional comments.
  24  */
  25
  26 #define JPEG_INTERNALS
  27 #include "jinclude.h"
  28 #include "jpeglib.h"
  29 #include "jdct.h"               /* Private declarations for DCT subsystem */
  30
  31 #ifdef IDCT_SCALING_SUPPORTED
  32
  33
  34 /*
  35  * This module is specialized to the case DCTSIZE = 8.
  36  */
  37
  38 #if DCTSIZE != 8
  39   Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
  40 #endif
  41
  42
  43 /* Scaling is the same as in jidctint.c. */
  44
  45 #if BITS_IN_JSAMPLE == 8
  46 #define CONST_BITS  13
  47 #define PASS1_BITS  2
  48 #else
  49 #define CONST_BITS  13
  50 #define PASS1_BITS  1           /* lose a little precision to avoid overflow */
  51 #endif
  52
  53 /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
  54  * causing a lot of useless floating-point operations at run time.
  55  * To get around this we use the following pre-calculated constants.
  56  * If you change CONST_BITS you may want to add appropriate values.
  57  * (With a reasonable C compiler, you can just rely on the FIX() macro...)
  58  */
  59
  60 #if CONST_BITS == 13
  61 #define FIX_0_211164243  ((JLONG)1730)          /* FIX(0.211164243) */
  62 #define FIX_0_509795579  ((JLONG)4176)          /* FIX(0.509795579) */
  63 #define FIX_0_601344887  ((JLONG)4926)          /* FIX(0.601344887) */
  64 #define FIX_0_720959822  ((JLONG)5906)          /* FIX(0.720959822) */
  65 #define FIX_0_765366865  ((JLONG)6270)          /* FIX(0.765366865) */
  66 #define FIX_0_850430095  ((JLONG)6967)          /* FIX(0.850430095) */
  67 #define FIX_0_899976223  ((JLONG)7373)          /* FIX(0.899976223) */
  68 #define FIX_1_061594337  ((JLONG)8697)          /* FIX(1.061594337) */
  69 #define FIX_1_272758580  ((JLONG)10426)         /* FIX(1.272758580) */
  70 #define FIX_1_451774981  ((JLONG)11893)         /* FIX(1.451774981) */
  71 #define FIX_1_847759065  ((JLONG)15137)         /* FIX(1.847759065) */
  72 #define FIX_2_172734803  ((JLONG)17799)         /* FIX(2.172734803) */
  73 #define FIX_2_562915447  ((JLONG)20995)         /* FIX(2.562915447) */
  74 #define FIX_3_624509785  ((JLONG)29692)         /* FIX(3.624509785) */
  75 #else
  76 #define FIX_0_211164243  FIX(0.211164243)
  77 #define FIX_0_509795579  FIX(0.509795579)
  78 #define FIX_0_601344887  FIX(0.601344887)
  79 #define FIX_0_720959822  FIX(0.720959822)
  80 #define FIX_0_765366865  FIX(0.765366865)
  81 #define FIX_0_850430095  FIX(0.850430095)
  82 #define FIX_0_899976223  FIX(0.899976223)
  83 #define FIX_1_061594337  FIX(1.061594337)
  84 #define FIX_1_272758580  FIX(1.272758580)
  85 #define FIX_1_451774981  FIX(1.451774981)
  86 #define FIX_1_847759065  FIX(1.847759065)
  87 #define FIX_2_172734803  FIX(2.172734803)
  88 #define FIX_2_562915447  FIX(2.562915447)
  89 #define FIX_3_624509785  FIX(3.624509785)
  90 #endif
  91
  92
  93 /* Multiply a JLONG variable by a JLONG constant to yield a JLONG result.
  94  * For 8-bit samples with the recommended scaling, all the variable
  95  * and constant values involved are no more than 16 bits wide, so a
  96  * 16x16->32 bit multiply can be used instead of a full 32x32 multiply.
  97  * For 12-bit samples, a full 32-bit multiplication will be needed.
  98  */
  99
 100 #if BITS_IN_JSAMPLE == 8
 101 #define MULTIPLY(var, const)  MULTIPLY16C16(var, const)
 102 #else
 103 #define MULTIPLY(var, const)  ((var) * (const))
 104 #endif
 105
 106
 107 /* Dequantize a coefficient by multiplying it by the multiplier-table
 108  * entry; produce an int result.  In this module, both inputs and result
 109  * are 16 bits or less, so either int or short multiply will work.
 110  */
 111
 112 #define DEQUANTIZE(coef, quantval)  (((ISLOW_MULT_TYPE)(coef)) * (quantval))
 113
 114
 115 /*
 116  * Perform dequantization and inverse DCT on one block of coefficients,
 117  * producing a reduced-size 4x4 output block.
 118  */
 119
 120 GLOBAL(void)
 121 jpeg_idct_4x4(j_decompress_ptr cinfo, jpeg_component_info *compptr,
 122               JCOEFPTR coef_block, JSAMPARRAY output_buf,
 123               JDIMENSION output_col)
 124 {
 125   JLONG tmp0, tmp2, tmp10, tmp12;
 126   JLONG z1, z2, z3, z4;
 127   JCOEFPTR inptr;
 128   ISLOW_MULT_TYPE *quantptr;
 129   int *wsptr;
 130   JSAMPROW outptr;
 131   JSAMPLE *range_limit = IDCT_range_limit(cinfo);
 132   int ctr;
 133   int workspace[DCTSIZE * 4];   /* buffers data between passes */
 134   SHIFT_TEMPS
 135
 136   /* Pass 1: process columns from input, store into work array. */
 137
 138   inptr = coef_block;
 139   quantptr = (ISLOW_MULT_TYPE *)compptr->dct_table;
 140   wsptr = workspace;
 141   for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) {
 142     /* Don't bother to process column 4, because second pass won't use it */
 143     if (ctr == DCTSIZE - 4)
 144       continue;
 145     if (inptr[DCTSIZE * 1] == 0 && inptr[DCTSIZE * 2] == 0 &&
 146         inptr[DCTSIZE * 3] == 0 && inptr[DCTSIZE * 5] == 0 &&
 147         inptr[DCTSIZE * 6] == 0 && inptr[DCTSIZE * 7] == 0) {
 148       /* AC terms all zero; we need not examine term 4 for 4x4 output */
 149       int dcval = LEFT_SHIFT(DEQUANTIZE(inptr[DCTSIZE * 0],
 150                                         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 = LEFT_SHIFT(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] =
 193       (int)DESCALE(tmp10 + tmp2, CONST_BITS - PASS1_BITS + 1);
 194     wsptr[DCTSIZE * 3] =
 195       (int)DESCALE(tmp10 - tmp2, CONST_BITS - PASS1_BITS + 1);
 196     wsptr[DCTSIZE * 1] =
 197       (int)DESCALE(tmp12 + tmp0, CONST_BITS - PASS1_BITS + 1);
 198     wsptr[DCTSIZE * 2] =
 199       (int)DESCALE(tmp12 - tmp0, CONST_BITS - PASS1_BITS + 1);
 200   }
 201
 202   /* Pass 2: process 4 rows from work array, store into output array. */
 203
 204   wsptr = workspace;
 205   for (ctr = 0; ctr < 4; ctr++) {
 206     outptr = output_buf[ctr] + output_col;
 207     /* It's not clear whether a zero row test is worthwhile here ... */
 208
 209 #ifndef NO_ZERO_ROW_TEST
 210     if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 &&
 211         wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) {
 212       /* AC terms all zero */
 213       JSAMPLE dcval = range_limit[(int)DESCALE((JLONG)wsptr[0],
 214                                                PASS1_BITS + 3) & RANGE_MASK];
 215
 216       outptr[0] = dcval;
 217       outptr[1] = dcval;
 218       outptr[2] = dcval;
 219       outptr[3] = dcval;
 220
 221       wsptr += DCTSIZE;         /* advance pointer to next row */
 222       continue;
 223     }
 224 #endif
 225
 226     /* Even part */
 227
 228     tmp0 = LEFT_SHIFT((JLONG)wsptr[0], CONST_BITS + 1);
 229
 230     tmp2 = MULTIPLY((JLONG)wsptr[2],  FIX_1_847759065) +
 231            MULTIPLY((JLONG)wsptr[6], -FIX_0_765366865);
 232
 233     tmp10 = tmp0 + tmp2;
 234     tmp12 = tmp0 - tmp2;
 235
 236     /* Odd part */
 237
 238     z1 = (JLONG)wsptr[7];
 239     z2 = (JLONG)wsptr[5];
 240     z3 = (JLONG)wsptr[3];
 241     z4 = (JLONG)wsptr[1];
 242
 243     tmp0 = MULTIPLY(z1, -FIX_0_211164243) + /* sqrt(2) * ( c3-c1) */
 244            MULTIPLY(z2,  FIX_1_451774981) + /* sqrt(2) * ( c3+c7) */
 245            MULTIPLY(z3, -FIX_2_172734803) + /* sqrt(2) * (-c1-c5) */
 246            MULTIPLY(z4,  FIX_1_061594337);  /* sqrt(2) * ( c5+c7) */
 247
 248     tmp2 = MULTIPLY(z1, -FIX_0_509795579) + /* sqrt(2) * (c7-c5) */
 249            MULTIPLY(z2, -FIX_0_601344887) + /* sqrt(2) * (c5-c1) */
 250            MULTIPLY(z3, FIX_0_899976223) +  /* sqrt(2) * (c3-c7) */
 251            MULTIPLY(z4, FIX_2_562915447);   /* sqrt(2) * (c1+c3) */
 252
 253     /* Final output stage */
 254
 255     outptr[0] = range_limit[(int)DESCALE(tmp10 + tmp2,
 256                                          CONST_BITS + PASS1_BITS + 3 + 1) &
 257                             RANGE_MASK];
 258     outptr[3] = range_limit[(int)DESCALE(tmp10 - tmp2,
 259                                          CONST_BITS + PASS1_BITS + 3 + 1) &
 260                             RANGE_MASK];
 261     outptr[1] = range_limit[(int)DESCALE(tmp12 + tmp0,
 262                                          CONST_BITS + PASS1_BITS + 3 + 1) &
 263                             RANGE_MASK];
 264     outptr[2] = range_limit[(int)DESCALE(tmp12 - tmp0,
 265                                          CONST_BITS + PASS1_BITS + 3 + 1) &
 266                             RANGE_MASK];
 267
 268     wsptr += DCTSIZE;           /* advance pointer to next row */
 269   }
 270 }
 271
 272
 273 /*
 274  * Perform dequantization and inverse DCT on one block of coefficients,
 275  * producing a reduced-size 2x2 output block.
 276  */
 277
 278 GLOBAL(void)
 279 jpeg_idct_2x2(j_decompress_ptr cinfo, jpeg_component_info *compptr,
 280               JCOEFPTR coef_block, JSAMPARRAY output_buf,
 281               JDIMENSION output_col)
 282 {
 283   JLONG tmp0, tmp10, z1;
 284   JCOEFPTR inptr;
 285   ISLOW_MULT_TYPE *quantptr;
 286   int *wsptr;
 287   JSAMPROW outptr;
 288   JSAMPLE *range_limit = IDCT_range_limit(cinfo);
 289   int ctr;
 290   int workspace[DCTSIZE * 2];   /* buffers data between passes */
 291   SHIFT_TEMPS
 292
 293   /* Pass 1: process columns from input, store into work array. */
 294
 295   inptr = coef_block;
 296   quantptr = (ISLOW_MULT_TYPE *)compptr->dct_table;
 297   wsptr = workspace;
 298   for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) {
 299     /* Don't bother to process columns 2,4,6 */
 300     if (ctr == DCTSIZE - 2 || ctr == DCTSIZE - 4 || ctr == DCTSIZE - 6)
 301       continue;
 302     if (inptr[DCTSIZE * 1] == 0 && inptr[DCTSIZE * 3] == 0 &&
 303         inptr[DCTSIZE * 5] == 0 && inptr[DCTSIZE * 7] == 0) {
 304       /* AC terms all zero; we need not examine terms 2,4,6 for 2x2 output */
 305       int dcval = LEFT_SHIFT(DEQUANTIZE(inptr[DCTSIZE * 0],
 306                              quantptr[DCTSIZE * 0]), PASS1_BITS);
 307
 308       wsptr[DCTSIZE * 0] = dcval;
 309       wsptr[DCTSIZE * 1] = dcval;
 310
 311       continue;
 312     }
 313
 314     /* Even part */
 315
 316     z1 = DEQUANTIZE(inptr[DCTSIZE * 0], quantptr[DCTSIZE * 0]);
 317     tmp10 = LEFT_SHIFT(z1, CONST_BITS + 2);
 318
 319     /* Odd part */
 320
 321     z1 = DEQUANTIZE(inptr[DCTSIZE * 7], quantptr[DCTSIZE * 7]);
 322     tmp0 = MULTIPLY(z1, -FIX_0_720959822);  /* sqrt(2) * ( c7-c5+c3-c1) */
 323     z1 = DEQUANTIZE(inptr[DCTSIZE * 5], quantptr[DCTSIZE * 5]);
 324     tmp0 += MULTIPLY(z1, FIX_0_850430095);  /* sqrt(2) * (-c1+c3+c5+c7) */
 325     z1 = DEQUANTIZE(inptr[DCTSIZE * 3], quantptr[DCTSIZE * 3]);
 326     tmp0 += MULTIPLY(z1, -FIX_1_272758580); /* sqrt(2) * (-c1+c3-c5-c7) */
 327     z1 = DEQUANTIZE(inptr[DCTSIZE * 1], quantptr[DCTSIZE * 1]);
 328     tmp0 += MULTIPLY(z1, FIX_3_624509785);  /* sqrt(2) * ( c1+c3+c5+c7) */
 329
 330     /* Final output stage */
 331
 332     wsptr[DCTSIZE * 0] =
 333       (int)DESCALE(tmp10 + tmp0, CONST_BITS - PASS1_BITS + 2);
 334     wsptr[DCTSIZE * 1] =
 335       (int)DESCALE(tmp10 - tmp0, CONST_BITS - PASS1_BITS + 2);
 336   }
 337
 338   /* Pass 2: process 2 rows from work array, store into output array. */
 339
 340   wsptr = workspace;
 341   for (ctr = 0; ctr < 2; ctr++) {
 342     outptr = output_buf[ctr] + output_col;
 343     /* It's not clear whether a zero row test is worthwhile here ... */
 344
 345 #ifndef NO_ZERO_ROW_TEST
 346     if (wsptr[1] == 0 && wsptr[3] == 0 && wsptr[5] == 0 && wsptr[7] == 0) {
 347       /* AC terms all zero */
 348       JSAMPLE dcval = range_limit[(int)DESCALE((JLONG)wsptr[0],
 349                                                PASS1_BITS + 3) & RANGE_MASK];
 350
 351       outptr[0] = dcval;
 352       outptr[1] = dcval;
 353
 354       wsptr += DCTSIZE;         /* advance pointer to next row */
 355       continue;
 356     }
 357 #endif
 358
 359     /* Even part */
 360
 361     tmp10 = LEFT_SHIFT((JLONG)wsptr[0], CONST_BITS + 2);
 362
 363     /* Odd part */
 364
 365     tmp0 = MULTIPLY((JLONG)wsptr[7], -FIX_0_720959822) + /* sqrt(2) * ( c7-c5+c3-c1) */
 366            MULTIPLY((JLONG)wsptr[5],  FIX_0_850430095) + /* sqrt(2) * (-c1+c3+c5+c7) */
 367            MULTIPLY((JLONG)wsptr[3], -FIX_1_272758580) + /* sqrt(2) * (-c1+c3-c5-c7) */
 368            MULTIPLY((JLONG)wsptr[1],  FIX_3_624509785);  /* sqrt(2) * ( c1+c3+c5+c7) */
 369
 370     /* Final output stage */
 371
 372     outptr[0] = range_limit[(int)DESCALE(tmp10 + tmp0,
 373                                          CONST_BITS + PASS1_BITS + 3 + 2) &
 374                             RANGE_MASK];
 375     outptr[1] = range_limit[(int)DESCALE(tmp10 - tmp0,
 376                                          CONST_BITS + PASS1_BITS + 3 + 2) &
 377                             RANGE_MASK];
 378
 379     wsptr += DCTSIZE;           /* advance pointer to next row */
 380   }
 381 }
 382
 383
 384 /*
 385  * Perform dequantization and inverse DCT on one block of coefficients,
 386  * producing a reduced-size 1x1 output block.
 387  */
 388
 389 GLOBAL(void)
 390 jpeg_idct_1x1(j_decompress_ptr cinfo, jpeg_component_info *compptr,
 391               JCOEFPTR coef_block, JSAMPARRAY output_buf,
 392               JDIMENSION output_col)
 393 {
 394   int dcval;
 395   ISLOW_MULT_TYPE *quantptr;
 396   JSAMPLE *range_limit = IDCT_range_limit(cinfo);
 397   SHIFT_TEMPS
 398
 399   /* We hardly need an inverse DCT routine for this: just take the
 400    * average pixel value, which is one-eighth of the DC coefficient.
 401    */
 402   quantptr = (ISLOW_MULT_TYPE *)compptr->dct_table;
 403   dcval = DEQUANTIZE(coef_block[0], quantptr[0]);
 404   dcval = (int)DESCALE((JLONG)dcval, 3);
 405
 406   output_buf[0][output_col] = range_limit[dcval & RANGE_MASK];
 407 }
 408
 409 #endif /* IDCT_SCALING_SUPPORTED */