libavcodec/jfdctfst.c

   1 /*
   2  * This file is part of the Independent JPEG Group's software.
   3  *
   4  * The authors make NO WARRANTY or representation, either express or implied,
   5  * with respect to this software, its quality, accuracy, merchantability, or
   6  * fitness for a particular purpose.  This software is provided "AS IS", and
   7  * you, its user, assume the entire risk as to its quality and accuracy.
   8  *
   9  * This software is copyright (C) 1994-1996, Thomas G. Lane.
  10  * All Rights Reserved except as specified below.
  11  *
  12  * Permission is hereby granted to use, copy, modify, and distribute this
  13  * software (or portions thereof) for any purpose, without fee, subject to
  14  * these conditions:
  15  * (1) If any part of the source code for this software is distributed, then
  16  * this README file must be included, with this copyright and no-warranty
  17  * notice unaltered; and any additions, deletions, or changes to the original
  18  * files must be clearly indicated in accompanying documentation.
  19  * (2) If only executable code is distributed, then the accompanying
  20  * documentation must state that "this software is based in part on the work
  21  * of the Independent JPEG Group".
  22  * (3) Permission for use of this software is granted only if the user accepts
  23  * full responsibility for any undesirable consequences; the authors accept
  24  * NO LIABILITY for damages of any kind.
  25  *
  26  * These conditions apply to any software derived from or based on the IJG
  27  * code, not just to the unmodified library.  If you use our work, you ought
  28  * to acknowledge us.
  29  *
  30  * Permission is NOT granted for the use of any IJG author's name or company
  31  * name in advertising or publicity relating to this software or products
  32  * derived from it.  This software may be referred to only as "the Independent
  33  * JPEG Group's software".
  34  *
  35  * We specifically permit and encourage the use of this software as the basis
  36  * of commercial products, provided that all warranty or liability claims are
  37  * assumed by the product vendor.
  38  *
  39  * This file contains a fast, not so accurate integer implementation of the
  40  * forward DCT (Discrete Cosine Transform).
  41  *
  42  * A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT
  43  * on each column.  Direct algorithms are also available, but they are
  44  * much more complex and seem not to be any faster when reduced to code.
  45  *
  46  * This implementation is based on Arai, Agui, and Nakajima's algorithm for
  47  * scaled DCT.  Their original paper (Trans. IEICE E-71(11):1095) is in
  48  * Japanese, but the algorithm is described in the Pennebaker & Mitchell
  49  * JPEG textbook (see REFERENCES section in file README).  The following code
  50  * is based directly on figure 4-8 in P&M.
  51  * While an 8-point DCT cannot be done in less than 11 multiplies, it is
  52  * possible to arrange the computation so that many of the multiplies are
  53  * simple scalings of the final outputs.  These multiplies can then be
  54  * folded into the multiplications or divisions by the JPEG quantization
  55  * table entries.  The AA&N method leaves only 5 multiplies and 29 adds
  56  * to be done in the DCT itself.
  57  * The primary disadvantage of this method is that with fixed-point math,
  58  * accuracy is lost due to imprecise representation of the scaled
  59  * quantization values.  The smaller the quantization table entry, the less
  60  * precise the scaled value, so this implementation does worse with high-
  61  * quality-setting files than with low-quality ones.
  62  */
  63
  64 /**
  65  * @file
  66  * Independent JPEG Group's fast AAN dct.
  67  */
  68
  69 #include <stdint.h>
  70 #include "libavutil/attributes.h"
  71 #include "fdctdsp.h"
  72
  73 #define DCTSIZE 8
  74 #define GLOBAL(x) x
  75 #define RIGHT_SHIFT(x, n) ((x) >> (n))
  76
  77 /*
  78  * This module is specialized to the case DCTSIZE = 8.
  79  */
  80
  81 #if DCTSIZE != 8
  82   Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
  83 #endif
  84
  85
  86 /* Scaling decisions are generally the same as in the LL&M algorithm;
  87  * see jfdctint.c for more details.  However, we choose to descale
  88  * (right shift) multiplication products as soon as they are formed,
  89  * rather than carrying additional fractional bits into subsequent additions.
  90  * This compromises accuracy slightly, but it lets us save a few shifts.
  91  * More importantly, 16-bit arithmetic is then adequate (for 8-bit samples)
  92  * everywhere except in the multiplications proper; this saves a good deal
  93  * of work on 16-bit-int machines.
  94  *
  95  * Again to save a few shifts, the intermediate results between pass 1 and
  96  * pass 2 are not upscaled, but are represented only to integral precision.
  97  *
  98  * A final compromise is to represent the multiplicative constants to only
  99  * 8 fractional bits, rather than 13.  This saves some shifting work on some
 100  * machines, and may also reduce the cost of multiplication (since there
 101  * are fewer one-bits in the constants).
 102  */
 103
 104 #define CONST_BITS  8
 105
 106
 107 /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
 108  * causing a lot of useless floating-point operations at run time.
 109  * To get around this we use the following pre-calculated constants.
 110  * If you change CONST_BITS you may want to add appropriate values.
 111  * (With a reasonable C compiler, you can just rely on the FIX() macro...)
 112  */
 113
 114 #if CONST_BITS == 8
 115 #define FIX_0_382683433  ((int32_t)   98)       /* FIX(0.382683433) */
 116 #define FIX_0_541196100  ((int32_t)  139)       /* FIX(0.541196100) */
 117 #define FIX_0_707106781  ((int32_t)  181)       /* FIX(0.707106781) */
 118 #define FIX_1_306562965  ((int32_t)  334)       /* FIX(1.306562965) */
 119 #else
 120 #define FIX_0_382683433  FIX(0.382683433)
 121 #define FIX_0_541196100  FIX(0.541196100)
 122 #define FIX_0_707106781  FIX(0.707106781)
 123 #define FIX_1_306562965  FIX(1.306562965)
 124 #endif
 125
 126
 127 /* We can gain a little more speed, with a further compromise in accuracy,
 128  * by omitting the addition in a descaling shift.  This yields an incorrectly
 129  * rounded result half the time...
 130  */
 131
 132 #ifndef USE_ACCURATE_ROUNDING
 133 #undef DESCALE
 134 #define DESCALE(x,n)  RIGHT_SHIFT(x, n)
 135 #endif
 136
 137
 138 /* Multiply a int16_t variable by an int32_t constant, and immediately
 139  * descale to yield a int16_t result.
 140  */
 141
 142 #define MULTIPLY(var,const)  ((int16_t) DESCALE((var) * (const), CONST_BITS))
 143
 144 static av_always_inline void row_fdct(int16_t * data){
 145   int tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
 146   int tmp10, tmp11, tmp12, tmp13;
 147   int z1, z2, z3, z4, z5, z11, z13;
 148   int16_t *dataptr;
 149   int ctr;
 150
 151   /* Pass 1: process rows. */
 152
 153   dataptr = data;
 154   for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
 155     tmp0 = dataptr[0] + dataptr[7];
 156     tmp7 = dataptr[0] - dataptr[7];
 157     tmp1 = dataptr[1] + dataptr[6];
 158     tmp6 = dataptr[1] - dataptr[6];
 159     tmp2 = dataptr[2] + dataptr[5];
 160     tmp5 = dataptr[2] - dataptr[5];
 161     tmp3 = dataptr[3] + dataptr[4];
 162     tmp4 = dataptr[3] - dataptr[4];
 163
 164     /* Even part */
 165
 166     tmp10 = tmp0 + tmp3;        /* phase 2 */
 167     tmp13 = tmp0 - tmp3;
 168     tmp11 = tmp1 + tmp2;
 169     tmp12 = tmp1 - tmp2;
 170
 171     dataptr[0] = tmp10 + tmp11; /* phase 3 */
 172     dataptr[4] = tmp10 - tmp11;
 173
 174     z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */
 175     dataptr[2] = tmp13 + z1;    /* phase 5 */
 176     dataptr[6] = tmp13 - z1;
 177
 178     /* Odd part */
 179
 180     tmp10 = tmp4 + tmp5;        /* phase 2 */
 181     tmp11 = tmp5 + tmp6;
 182     tmp12 = tmp6 + tmp7;
 183
 184     /* The rotator is modified from fig 4-8 to avoid extra negations. */
 185     z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */
 186     z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5;    /* c2-c6 */
 187     z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5;    /* c2+c6 */
 188     z3 = MULTIPLY(tmp11, FIX_0_707106781);         /* c4 */
 189
 190     z11 = tmp7 + z3;            /* phase 5 */
 191     z13 = tmp7 - z3;
 192
 193     dataptr[5] = z13 + z2;      /* phase 6 */
 194     dataptr[3] = z13 - z2;
 195     dataptr[1] = z11 + z4;
 196     dataptr[7] = z11 - z4;
 197
 198     dataptr += DCTSIZE;         /* advance pointer to next row */
 199   }
 200 }
 201
 202 /*
 203  * Perform the forward DCT on one block of samples.
 204  */
 205
 206 GLOBAL(void)
 207 ff_fdct_ifast (int16_t * data)
 208 {
 209   int tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
 210   int tmp10, tmp11, tmp12, tmp13;
 211   int z1, z2, z3, z4, z5, z11, z13;
 212   int16_t *dataptr;
 213   int ctr;
 214
 215   row_fdct(data);
 216
 217   /* Pass 2: process columns. */
 218
 219   dataptr = data;
 220   for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
 221     tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];
 222     tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];
 223     tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];
 224     tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];
 225     tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];
 226     tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];
 227     tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];
 228     tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];
 229
 230     /* Even part */
 231
 232     tmp10 = tmp0 + tmp3;        /* phase 2 */
 233     tmp13 = tmp0 - tmp3;
 234     tmp11 = tmp1 + tmp2;
 235     tmp12 = tmp1 - tmp2;
 236
 237     dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */
 238     dataptr[DCTSIZE*4] = tmp10 - tmp11;
 239
 240     z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */
 241     dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */
 242     dataptr[DCTSIZE*6] = tmp13 - z1;
 243
 244     /* Odd part */
 245
 246     tmp10 = tmp4 + tmp5;        /* phase 2 */
 247     tmp11 = tmp5 + tmp6;
 248     tmp12 = tmp6 + tmp7;
 249
 250     /* The rotator is modified from fig 4-8 to avoid extra negations. */
 251     z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */
 252     z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */
 253     z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */
 254     z3 = MULTIPLY(tmp11, FIX_0_707106781); /* c4 */
 255
 256     z11 = tmp7 + z3;            /* phase 5 */
 257     z13 = tmp7 - z3;
 258
 259     dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */
 260     dataptr[DCTSIZE*3] = z13 - z2;
 261     dataptr[DCTSIZE*1] = z11 + z4;
 262     dataptr[DCTSIZE*7] = z11 - z4;
 263
 264     dataptr++;                  /* advance pointer to next column */
 265   }
 266 }
 267
 268 /*
 269  * Perform the forward 2-4-8 DCT on one block of samples.
 270  */
 271
 272 GLOBAL(void)
 273 ff_fdct_ifast248 (int16_t * data)
 274 {
 275   int tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
 276   int tmp10, tmp11, tmp12, tmp13;
 277   int z1;
 278   int16_t *dataptr;
 279   int ctr;
 280
 281   row_fdct(data);
 282
 283   /* Pass 2: process columns. */
 284
 285   dataptr = data;
 286   for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
 287     tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*1];
 288     tmp1 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*3];
 289     tmp2 = dataptr[DCTSIZE*4] + dataptr[DCTSIZE*5];
 290     tmp3 = dataptr[DCTSIZE*6] + dataptr[DCTSIZE*7];
 291     tmp4 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*1];
 292     tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*3];
 293     tmp6 = dataptr[DCTSIZE*4] - dataptr[DCTSIZE*5];
 294     tmp7 = dataptr[DCTSIZE*6] - dataptr[DCTSIZE*7];
 295
 296     /* Even part */
 297
 298     tmp10 = tmp0 + tmp3;
 299     tmp11 = tmp1 + tmp2;
 300     tmp12 = tmp1 - tmp2;
 301     tmp13 = tmp0 - tmp3;
 302
 303     dataptr[DCTSIZE*0] = tmp10 + tmp11;
 304     dataptr[DCTSIZE*4] = tmp10 - tmp11;
 305
 306     z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781);
 307     dataptr[DCTSIZE*2] = tmp13 + z1;
 308     dataptr[DCTSIZE*6] = tmp13 - z1;
 309
 310     tmp10 = tmp4 + tmp7;
 311     tmp11 = tmp5 + tmp6;
 312     tmp12 = tmp5 - tmp6;
 313     tmp13 = tmp4 - tmp7;
 314
 315     dataptr[DCTSIZE*1] = tmp10 + tmp11;
 316     dataptr[DCTSIZE*5] = tmp10 - tmp11;
 317
 318     z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781);
 319     dataptr[DCTSIZE*3] = tmp13 + z1;
 320     dataptr[DCTSIZE*7] = tmp13 - z1;
 321
 322     dataptr++;                        /* advance pointer to next column */
 323   }
 324 }
 325
 326
 327 #undef GLOBAL
 328 #undef CONST_BITS
 329 #undef DESCALE
 330 #undef FIX_0_541196100
 331 #undef FIX_1_306562965