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 <stdlib.h>
  70 #include <stdio.h>
  71 #include "libavutil/common.h"
  72 #include "dct.h"
  73
  74 #define DCTSIZE 8
  75 #define GLOBAL(x) x
  76 #define RIGHT_SHIFT(x, n) ((x) >> (n))
  77
  78 /*
  79  * This module is specialized to the case DCTSIZE = 8.
  80  */
  81
  82 #if DCTSIZE != 8
  83   Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
  84 #endif
  85
  86
  87 /* Scaling decisions are generally the same as in the LL&M algorithm;
  88  * see jfdctint.c for more details.  However, we choose to descale
  89  * (right shift) multiplication products as soon as they are formed,
  90  * rather than carrying additional fractional bits into subsequent additions.
  91  * This compromises accuracy slightly, but it lets us save a few shifts.
  92  * More importantly, 16-bit arithmetic is then adequate (for 8-bit samples)
  93  * everywhere except in the multiplications proper; this saves a good deal
  94  * of work on 16-bit-int machines.
  95  *
  96  * Again to save a few shifts, the intermediate results between pass 1 and
  97  * pass 2 are not upscaled, but are represented only to integral precision.
  98  *
  99  * A final compromise is to represent the multiplicative constants to only
 100  * 8 fractional bits, rather than 13.  This saves some shifting work on some
 101  * machines, and may also reduce the cost of multiplication (since there
 102  * are fewer one-bits in the constants).
 103  */
 104
 105 #define CONST_BITS  8
 106
 107
 108 /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
 109  * causing a lot of useless floating-point operations at run time.
 110  * To get around this we use the following pre-calculated constants.
 111  * If you change CONST_BITS you may want to add appropriate values.
 112  * (With a reasonable C compiler, you can just rely on the FIX() macro...)
 113  */
 114
 115 #if CONST_BITS == 8
 116 #define FIX_0_382683433  ((int32_t)   98)       /* FIX(0.382683433) */
 117 #define FIX_0_541196100  ((int32_t)  139)       /* FIX(0.541196100) */
 118 #define FIX_0_707106781  ((int32_t)  181)       /* FIX(0.707106781) */
 119 #define FIX_1_306562965  ((int32_t)  334)       /* FIX(1.306562965) */
 120 #else
 121 #define FIX_0_382683433  FIX(0.382683433)
 122 #define FIX_0_541196100  FIX(0.541196100)
 123 #define FIX_0_707106781  FIX(0.707106781)
 124 #define FIX_1_306562965  FIX(1.306562965)
 125 #endif
 126
 127
 128 /* We can gain a little more speed, with a further compromise in accuracy,
 129  * by omitting the addition in a descaling shift.  This yields an incorrectly
 130  * rounded result half the time...
 131  */
 132
 133 #ifndef USE_ACCURATE_ROUNDING
 134 #undef DESCALE
 135 #define DESCALE(x,n)  RIGHT_SHIFT(x, n)
 136 #endif
 137
 138
 139 /* Multiply a int16_t variable by an int32_t constant, and immediately
 140  * descale to yield a int16_t result.
 141  */
 142
 143 #define MULTIPLY(var,const)  ((int16_t) DESCALE((var) * (const), CONST_BITS))
 144
 145 static av_always_inline void row_fdct(int16_t * data){
 146   int tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
 147   int tmp10, tmp11, tmp12, tmp13;
 148   int z1, z2, z3, z4, z5, z11, z13;
 149   int16_t *dataptr;
 150   int ctr;
 151
 152   /* Pass 1: process rows. */
 153
 154   dataptr = data;
 155   for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
 156     tmp0 = dataptr[0] + dataptr[7];
 157     tmp7 = dataptr[0] - dataptr[7];
 158     tmp1 = dataptr[1] + dataptr[6];
 159     tmp6 = dataptr[1] - dataptr[6];
 160     tmp2 = dataptr[2] + dataptr[5];
 161     tmp5 = dataptr[2] - dataptr[5];
 162     tmp3 = dataptr[3] + dataptr[4];
 163     tmp4 = dataptr[3] - dataptr[4];
 164
 165     /* Even part */
 166
 167     tmp10 = tmp0 + tmp3;        /* phase 2 */
 168     tmp13 = tmp0 - tmp3;
 169     tmp11 = tmp1 + tmp2;
 170     tmp12 = tmp1 - tmp2;
 171
 172     dataptr[0] = tmp10 + tmp11; /* phase 3 */
 173     dataptr[4] = tmp10 - tmp11;
 174
 175     z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */
 176     dataptr[2] = tmp13 + z1;    /* phase 5 */
 177     dataptr[6] = tmp13 - z1;
 178
 179     /* Odd part */
 180
 181     tmp10 = tmp4 + tmp5;        /* phase 2 */
 182     tmp11 = tmp5 + tmp6;
 183     tmp12 = tmp6 + tmp7;
 184
 185     /* The rotator is modified from fig 4-8 to avoid extra negations. */
 186     z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */
 187     z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5;    /* c2-c6 */
 188     z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5;    /* c2+c6 */
 189     z3 = MULTIPLY(tmp11, FIX_0_707106781);         /* c4 */
 190
 191     z11 = tmp7 + z3;            /* phase 5 */
 192     z13 = tmp7 - z3;
 193
 194     dataptr[5] = z13 + z2;      /* phase 6 */
 195     dataptr[3] = z13 - z2;
 196     dataptr[1] = z11 + z4;
 197     dataptr[7] = z11 - z4;
 198
 199     dataptr += DCTSIZE;         /* advance pointer to next row */
 200   }
 201 }
 202
 203 /*
 204  * Perform the forward DCT on one block of samples.
 205  */
 206
 207 GLOBAL(void)
 208 ff_fdct_ifast (int16_t * data)
 209 {
 210   int tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
 211   int tmp10, tmp11, tmp12, tmp13;
 212   int z1, z2, z3, z4, z5, z11, z13;
 213   int16_t *dataptr;
 214   int ctr;
 215
 216   row_fdct(data);
 217
 218   /* Pass 2: process columns. */
 219
 220   dataptr = data;
 221   for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
 222     tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];
 223     tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];
 224     tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];
 225     tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];
 226     tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];
 227     tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];
 228     tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];
 229     tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];
 230
 231     /* Even part */
 232
 233     tmp10 = tmp0 + tmp3;        /* phase 2 */
 234     tmp13 = tmp0 - tmp3;
 235     tmp11 = tmp1 + tmp2;
 236     tmp12 = tmp1 - tmp2;
 237
 238     dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */
 239     dataptr[DCTSIZE*4] = tmp10 - tmp11;
 240
 241     z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */
 242     dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */
 243     dataptr[DCTSIZE*6] = tmp13 - z1;
 244
 245     /* Odd part */
 246
 247     tmp10 = tmp4 + tmp5;        /* phase 2 */
 248     tmp11 = tmp5 + tmp6;
 249     tmp12 = tmp6 + tmp7;
 250
 251     /* The rotator is modified from fig 4-8 to avoid extra negations. */
 252     z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */
 253     z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */
 254     z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */
 255     z3 = MULTIPLY(tmp11, FIX_0_707106781); /* c4 */
 256
 257     z11 = tmp7 + z3;            /* phase 5 */
 258     z13 = tmp7 - z3;
 259
 260     dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */
 261     dataptr[DCTSIZE*3] = z13 - z2;
 262     dataptr[DCTSIZE*1] = z11 + z4;
 263     dataptr[DCTSIZE*7] = z11 - z4;
 264
 265     dataptr++;                  /* advance pointer to next column */
 266   }
 267 }
 268
 269 /*
 270  * Perform the forward 2-4-8 DCT on one block of samples.
 271  */
 272
 273 GLOBAL(void)
 274 ff_fdct_ifast248 (int16_t * data)
 275 {
 276   int tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
 277   int tmp10, tmp11, tmp12, tmp13;
 278   int z1;
 279   int16_t *dataptr;
 280   int ctr;
 281
 282   row_fdct(data);
 283
 284   /* Pass 2: process columns. */
 285
 286   dataptr = data;
 287   for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
 288     tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*1];
 289     tmp1 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*3];
 290     tmp2 = dataptr[DCTSIZE*4] + dataptr[DCTSIZE*5];
 291     tmp3 = dataptr[DCTSIZE*6] + dataptr[DCTSIZE*7];
 292     tmp4 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*1];
 293     tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*3];
 294     tmp6 = dataptr[DCTSIZE*4] - dataptr[DCTSIZE*5];
 295     tmp7 = dataptr[DCTSIZE*6] - dataptr[DCTSIZE*7];
 296
 297     /* Even part */
 298
 299     tmp10 = tmp0 + tmp3;
 300     tmp11 = tmp1 + tmp2;
 301     tmp12 = tmp1 - tmp2;
 302     tmp13 = tmp0 - tmp3;
 303
 304     dataptr[DCTSIZE*0] = tmp10 + tmp11;
 305     dataptr[DCTSIZE*4] = tmp10 - tmp11;
 306
 307     z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781);
 308     dataptr[DCTSIZE*2] = tmp13 + z1;
 309     dataptr[DCTSIZE*6] = tmp13 - z1;
 310
 311     tmp10 = tmp4 + tmp7;
 312     tmp11 = tmp5 + tmp6;
 313     tmp12 = tmp5 - tmp6;
 314     tmp13 = tmp4 - tmp7;
 315
 316     dataptr[DCTSIZE*1] = tmp10 + tmp11;
 317     dataptr[DCTSIZE*5] = tmp10 - tmp11;
 318
 319     z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781);
 320     dataptr[DCTSIZE*3] = tmp13 + z1;
 321     dataptr[DCTSIZE*7] = tmp13 - z1;
 322
 323     dataptr++;                        /* advance pointer to next column */
 324   }
 325 }
 326
 327
 328 #undef GLOBAL
 329 #undef CONST_BITS
 330 #undef DESCALE
 331 #undef FIX_0_541196100
 332 #undef FIX_1_306562965