extern/ffmpeg/libavcodec/jfdctfst.c

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