libavcodec/jfdctfst.c

   1 /*
   2  * jfdctfst.c
   3  *
   4  * This file is part of the Independent JPEG Group's software.
   5  *
   6  * The authors make NO WARRANTY or representation, either express or implied,
   7  * with respect to this software, its quality, accuracy, merchantability, or
   8  * fitness for a particular purpose.  This software is provided "AS IS", and
   9  * you, its user, assume the entire risk as to its quality and accuracy.
  10  *
  11  * This software is copyright (C) 1994-1996, Thomas G. Lane.
  12  * All Rights Reserved except as specified below.
  13  *
  14  * Permission is hereby granted to use, copy, modify, and distribute this
  15  * software (or portions thereof) for any purpose, without fee, subject to
  16  * these conditions:
  17  * (1) If any part of the source code for this software is distributed, then
  18  * this README file must be included, with this copyright and no-warranty
  19  * notice unaltered; and any additions, deletions, or changes to the original
  20  * files must be clearly indicated in accompanying documentation.
  21  * (2) If only executable code is distributed, then the accompanying
  22  * documentation must state that "this software is based in part on the work
  23  * of the Independent JPEG Group".
  24  * (3) Permission for use of this software is granted only if the user accepts
  25  * full responsibility for any undesirable consequences; the authors accept
  26  * NO LIABILITY for damages of any kind.
  27  *
  28  * These conditions apply to any software derived from or based on the IJG
  29  * code, not just to the unmodified library.  If you use our work, you ought
  30  * to acknowledge us.
  31  *
  32  * Permission is NOT granted for the use of any IJG author's name or company
  33  * name in advertising or publicity relating to this software or products
  34  * derived from it.  This software may be referred to only as "the Independent
  35  * JPEG Group's software".
  36  *
  37  * We specifically permit and encourage the use of this software as the basis
  38  * of commercial products, provided that all warranty or liability claims are
  39  * assumed by the product vendor.
  40  *
  41  * This file contains a fast, not so accurate integer implementation of the
  42  * forward DCT (Discrete Cosine Transform).
  43  *
  44  * A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT
  45  * on each column.  Direct algorithms are also available, but they are
  46  * much more complex and seem not to be any faster when reduced to code.
  47  *
  48  * This implementation is based on Arai, Agui, and Nakajima's algorithm for
  49  * scaled DCT.  Their original paper (Trans. IEICE E-71(11):1095) is in
  50  * Japanese, but the algorithm is described in the Pennebaker & Mitchell
  51  * JPEG textbook (see REFERENCES section in file README).  The following code
  52  * is based directly on figure 4-8 in P&M.
  53  * While an 8-point DCT cannot be done in less than 11 multiplies, it is
  54  * possible to arrange the computation so that many of the multiplies are
  55  * simple scalings of the final outputs.  These multiplies can then be
  56  * folded into the multiplications or divisions by the JPEG quantization
  57  * table entries.  The AA&N method leaves only 5 multiplies and 29 adds
  58  * to be done in the DCT itself.
  59  * The primary disadvantage of this method is that with fixed-point math,
  60  * accuracy is lost due to imprecise representation of the scaled
  61  * quantization values.  The smaller the quantization table entry, the less
  62  * precise the scaled value, so this implementation does worse with high-
  63  * quality-setting files than with low-quality ones.
  64  */
  65
  66 /**
  67  * @file libavcodec/jfdctfst.c
  68  * Independent JPEG Group's fast AAN dct.
  69  */
  70
  71 #include <stdlib.h>
  72 #include <stdio.h>
  73 #include "libavutil/common.h"
  74 #include "dsputil.h"
  75
  76 #define DCTSIZE 8
  77 #define GLOBAL(x) x
  78 #define RIGHT_SHIFT(x, n) ((x) >> (n))
  79
  80 /*
  81  * This module is specialized to the case DCTSIZE = 8.
  82  */
  83
  84 #if DCTSIZE != 8
  85   Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
  86 #endif
  87
  88
  89 /* Scaling decisions are generally the same as in the LL&M algorithm;
  90  * see jfdctint.c for more details.  However, we choose to descale
  91  * (right shift) multiplication products as soon as they are formed,
  92  * rather than carrying additional fractional bits into subsequent additions.
  93  * This compromises accuracy slightly, but it lets us save a few shifts.
  94  * More importantly, 16-bit arithmetic is then adequate (for 8-bit samples)
  95  * everywhere except in the multiplications proper; this saves a good deal
  96  * of work on 16-bit-int machines.
  97  *
  98  * Again to save a few shifts, the intermediate results between pass 1 and
  99  * pass 2 are not upscaled, but are represented only to integral precision.
 100  *
 101  * A final compromise is to represent the multiplicative constants to only
 102  * 8 fractional bits, rather than 13.  This saves some shifting work on some
 103  * machines, and may also reduce the cost of multiplication (since there
 104  * are fewer one-bits in the constants).
 105  */
 106
 107 #define CONST_BITS  8
 108
 109
 110 /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
 111  * causing a lot of useless floating-point operations at run time.
 112  * To get around this we use the following pre-calculated constants.
 113  * If you change CONST_BITS you may want to add appropriate values.
 114  * (With a reasonable C compiler, you can just rely on the FIX() macro...)
 115  */
 116
 117 #if CONST_BITS == 8
 118 #define FIX_0_382683433  ((int32_t)   98)       /* FIX(0.382683433) */
 119 #define FIX_0_541196100  ((int32_t)  139)       /* FIX(0.541196100) */
 120 #define FIX_0_707106781  ((int32_t)  181)       /* FIX(0.707106781) */
 121 #define FIX_1_306562965  ((int32_t)  334)       /* FIX(1.306562965) */
 122 #else
 123 #define FIX_0_382683433  FIX(0.382683433)
 124 #define FIX_0_541196100  FIX(0.541196100)
 125 #define FIX_0_707106781  FIX(0.707106781)
 126 #define FIX_1_306562965  FIX(1.306562965)
 127 #endif
 128
 129
 130 /* We can gain a little more speed, with a further compromise in accuracy,
 131  * by omitting the addition in a descaling shift.  This yields an incorrectly
 132  * rounded result half the time...
 133  */
 134
 135 #ifndef USE_ACCURATE_ROUNDING
 136 #undef DESCALE
 137 #define DESCALE(x,n)  RIGHT_SHIFT(x, n)
 138 #endif
 139
 140
 141 /* Multiply a DCTELEM variable by an int32_t constant, and immediately
 142  * descale to yield a DCTELEM result.
 143  */
 144
 145 #define MULTIPLY(var,const)  ((DCTELEM) DESCALE((var) * (const), CONST_BITS))
 146
 147 static av_always_inline void row_fdct(DCTELEM * data){
 148   int_fast16_t tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
 149   int_fast16_t tmp10, tmp11, tmp12, tmp13;
 150   int_fast16_t z1, z2, z3, z4, z5, z11, z13;
 151   DCTELEM *dataptr;
 152   int ctr;
 153
 154   /* Pass 1: process rows. */
 155
 156   dataptr = data;
 157   for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
 158     tmp0 = dataptr[0] + dataptr[7];
 159     tmp7 = dataptr[0] - dataptr[7];
 160     tmp1 = dataptr[1] + dataptr[6];
 161     tmp6 = dataptr[1] - dataptr[6];
 162     tmp2 = dataptr[2] + dataptr[5];
 163     tmp5 = dataptr[2] - dataptr[5];
 164     tmp3 = dataptr[3] + dataptr[4];
 165     tmp4 = dataptr[3] - dataptr[4];
 166
 167     /* Even part */
 168
 169     tmp10 = tmp0 + tmp3;        /* phase 2 */
 170     tmp13 = tmp0 - tmp3;
 171     tmp11 = tmp1 + tmp2;
 172     tmp12 = tmp1 - tmp2;
 173
 174     dataptr[0] = tmp10 + tmp11; /* phase 3 */
 175     dataptr[4] = tmp10 - tmp11;
 176
 177     z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */
 178     dataptr[2] = tmp13 + z1;    /* phase 5 */
 179     dataptr[6] = tmp13 - z1;
 180
 181     /* Odd part */
 182
 183     tmp10 = tmp4 + tmp5;        /* phase 2 */
 184     tmp11 = tmp5 + tmp6;
 185     tmp12 = tmp6 + tmp7;
 186
 187     /* The rotator is modified from fig 4-8 to avoid extra negations. */
 188     z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */
 189     z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5;    /* c2-c6 */
 190     z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5;    /* c2+c6 */
 191     z3 = MULTIPLY(tmp11, FIX_0_707106781);         /* c4 */
 192
 193     z11 = tmp7 + z3;            /* phase 5 */
 194     z13 = tmp7 - z3;
 195
 196     dataptr[5] = z13 + z2;      /* phase 6 */
 197     dataptr[3] = z13 - z2;
 198     dataptr[1] = z11 + z4;
 199     dataptr[7] = z11 - z4;
 200
 201     dataptr += DCTSIZE;         /* advance pointer to next row */
 202   }
 203 }
 204
 205 /*
 206  * Perform the forward DCT on one block of samples.
 207  */
 208
 209 GLOBAL(void)
 210 fdct_ifast (DCTELEM * data)
 211 {
 212   int_fast16_t tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
 213   int_fast16_t tmp10, tmp11, tmp12, tmp13;
 214   int_fast16_t z1, z2, z3, z4, z5, z11, z13;
 215   DCTELEM *dataptr;
 216   int ctr;
 217
 218   row_fdct(data);
 219
 220   /* Pass 2: process columns. */
 221
 222   dataptr = data;
 223   for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
 224     tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];
 225     tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];
 226     tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];
 227     tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];
 228     tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];
 229     tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];
 230     tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];
 231     tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];
 232
 233     /* Even part */
 234
 235     tmp10 = tmp0 + tmp3;        /* phase 2 */
 236     tmp13 = tmp0 - tmp3;
 237     tmp11 = tmp1 + tmp2;
 238     tmp12 = tmp1 - tmp2;
 239
 240     dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */
 241     dataptr[DCTSIZE*4] = tmp10 - tmp11;
 242
 243     z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */
 244     dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */
 245     dataptr[DCTSIZE*6] = tmp13 - z1;
 246
 247     /* Odd part */
 248
 249     tmp10 = tmp4 + tmp5;        /* phase 2 */
 250     tmp11 = tmp5 + tmp6;
 251     tmp12 = tmp6 + tmp7;
 252
 253     /* The rotator is modified from fig 4-8 to avoid extra negations. */
 254     z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */
 255     z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */
 256     z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */
 257     z3 = MULTIPLY(tmp11, FIX_0_707106781); /* c4 */
 258
 259     z11 = tmp7 + z3;            /* phase 5 */
 260     z13 = tmp7 - z3;
 261
 262     dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */
 263     dataptr[DCTSIZE*3] = z13 - z2;
 264     dataptr[DCTSIZE*1] = z11 + z4;
 265     dataptr[DCTSIZE*7] = z11 - z4;
 266
 267     dataptr++;                  /* advance pointer to next column */
 268   }
 269 }
 270
 271 /*
 272  * Perform the forward 2-4-8 DCT on one block of samples.
 273  */
 274
 275 GLOBAL(void)
 276 fdct_ifast248 (DCTELEM * data)
 277 {
 278   int_fast16_t tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
 279   int_fast16_t tmp10, tmp11, tmp12, tmp13;
 280   int_fast16_t z1;
 281   DCTELEM *dataptr;
 282   int ctr;
 283
 284   row_fdct(data);
 285
 286   /* Pass 2: process columns. */
 287
 288   dataptr = data;
 289   for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
 290     tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*1];
 291     tmp1 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*3];
 292     tmp2 = dataptr[DCTSIZE*4] + dataptr[DCTSIZE*5];
 293     tmp3 = dataptr[DCTSIZE*6] + dataptr[DCTSIZE*7];
 294     tmp4 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*1];
 295     tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*3];
 296     tmp6 = dataptr[DCTSIZE*4] - dataptr[DCTSIZE*5];
 297     tmp7 = dataptr[DCTSIZE*6] - dataptr[DCTSIZE*7];
 298
 299     /* Even part */
 300
 301     tmp10 = tmp0 + tmp3;
 302     tmp11 = tmp1 + tmp2;
 303     tmp12 = tmp1 - tmp2;
 304     tmp13 = tmp0 - tmp3;
 305
 306     dataptr[DCTSIZE*0] = tmp10 + tmp11;
 307     dataptr[DCTSIZE*4] = tmp10 - tmp11;
 308
 309     z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781);
 310     dataptr[DCTSIZE*2] = tmp13 + z1;
 311     dataptr[DCTSIZE*6] = tmp13 - z1;
 312
 313     tmp10 = tmp4 + tmp7;
 314     tmp11 = tmp5 + tmp6;
 315     tmp12 = tmp5 - tmp6;
 316     tmp13 = tmp4 - tmp7;
 317
 318     dataptr[DCTSIZE*1] = tmp10 + tmp11;
 319     dataptr[DCTSIZE*5] = tmp10 - tmp11;
 320
 321     z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781);
 322     dataptr[DCTSIZE*3] = tmp13 + z1;
 323     dataptr[DCTSIZE*7] = tmp13 - z1;
 324
 325     dataptr++;                        /* advance pointer to next column */
 326   }
 327 }
 328
 329
 330 #undef GLOBAL
 331 #undef CONST_BITS
 332 #undef DESCALE
 333 #undef FIX_0_541196100
 334 #undef FIX_1_306562965