ffmpeg/libavcodec/dct.c

   1 /*
   2  * (I)DCT Transforms
   3  * Copyright (c) 2009 Peter Ross <pross@xvid.org>
   4  * Copyright (c) 2010 Alex Converse <alex.converse@gmail.com>
   5  * Copyright (c) 2010 Vitor Sessak
   6  *
   7  * This file is part of FFmpeg.
   8  *
   9  * FFmpeg is free software; you can redistribute it and/or
  10  * modify it under the terms of the GNU Lesser General Public
  11  * License as published by the Free Software Foundation; either
  12  * version 2.1 of the License, or (at your option) any later version.
  13  *
  14  * FFmpeg is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  17  * Lesser General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU Lesser General Public
  20  * License along with FFmpeg; if not, write to the Free Software
  21  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  22  */
  23
  24 /**
  25  * @file
  26  * (Inverse) Discrete Cosine Transforms. These are also known as the
  27  * type II and type III DCTs respectively.
  28  */
  29
  30 #include <math.h>
  31 #include <string.h>
  32
  33 #include "libavutil/mathematics.h"
  34 #include "dct.h"
  35 #include "dct32.h"
  36
  37 /* sin((M_PI * x / (2 * n)) */
  38 #define SIN(s, n, x) (s->costab[(n) - (x)])
  39
  40 /* cos((M_PI * x / (2 * n)) */
  41 #define COS(s, n, x) (s->costab[x])
  42
  43 static void dst_calc_I_c(DCTContext *ctx, FFTSample *data)
  44 {
  45     int n = 1 << ctx->nbits;
  46     int i;
  47
  48     data[0] = 0;
  49     for (i = 1; i < n / 2; i++) {
  50         float tmp1   = data[i    ];
  51         float tmp2   = data[n - i];
  52         float s      = SIN(ctx, n, 2 * i);
  53
  54         s           *= tmp1 + tmp2;
  55         tmp1         = (tmp1 - tmp2) * 0.5f;
  56         data[i]      = s + tmp1;
  57         data[n - i]  = s - tmp1;
  58     }
  59
  60     data[n / 2] *= 2;
  61     ctx->rdft.rdft_calc(&ctx->rdft, data);
  62
  63     data[0] *= 0.5f;
  64
  65     for (i = 1; i < n - 2; i += 2) {
  66         data[i + 1] +=  data[i - 1];
  67         data[i]      = -data[i + 2];
  68     }
  69
  70     data[n - 1] = 0;
  71 }
  72
  73 static void dct_calc_I_c(DCTContext *ctx, FFTSample *data)
  74 {
  75     int n = 1 << ctx->nbits;
  76     int i;
  77     float next = -0.5f * (data[0] - data[n]);
  78
  79     for (i = 0; i < n / 2; i++) {
  80         float tmp1 = data[i];
  81         float tmp2 = data[n - i];
  82         float s    = SIN(ctx, n, 2 * i);
  83         float c    = COS(ctx, n, 2 * i);
  84
  85         c *= tmp1 - tmp2;
  86         s *= tmp1 - tmp2;
  87
  88         next += c;
  89
  90         tmp1        = (tmp1 + tmp2) * 0.5f;
  91         data[i]     = tmp1 - s;
  92         data[n - i] = tmp1 + s;
  93     }
  94
  95     ctx->rdft.rdft_calc(&ctx->rdft, data);
  96     data[n] = data[1];
  97     data[1] = next;
  98
  99     for (i = 3; i <= n; i += 2)
 100         data[i] = data[i - 2] - data[i];
 101 }
 102
 103 static void dct_calc_III_c(DCTContext *ctx, FFTSample *data)
 104 {
 105     int n = 1 << ctx->nbits;
 106     int i;
 107
 108     float next  = data[n - 1];
 109     float inv_n = 1.0f / n;
 110
 111     for (i = n - 2; i >= 2; i -= 2) {
 112         float val1 = data[i];
 113         float val2 = data[i - 1] - data[i + 1];
 114         float c    = COS(ctx, n, i);
 115         float s    = SIN(ctx, n, i);
 116
 117         data[i]     = c * val1 + s * val2;
 118         data[i + 1] = s * val1 - c * val2;
 119     }
 120
 121     data[1] = 2 * next;
 122
 123     ctx->rdft.rdft_calc(&ctx->rdft, data);
 124
 125     for (i = 0; i < n / 2; i++) {
 126         float tmp1 = data[i]         * inv_n;
 127         float tmp2 = data[n - i - 1] * inv_n;
 128         float csc  = ctx->csc2[i] * (tmp1 - tmp2);
 129
 130         tmp1            += tmp2;
 131         data[i]          = tmp1 + csc;
 132         data[n - i - 1]  = tmp1 - csc;
 133     }
 134 }
 135
 136 static void dct_calc_II_c(DCTContext *ctx, FFTSample *data)
 137 {
 138     int n = 1 << ctx->nbits;
 139     int i;
 140     float next;
 141
 142     for (i = 0; i < n / 2; i++) {
 143         float tmp1 = data[i];
 144         float tmp2 = data[n - i - 1];
 145         float s    = SIN(ctx, n, 2 * i + 1);
 146
 147         s    *= tmp1 - tmp2;
 148         tmp1  = (tmp1 + tmp2) * 0.5f;
 149
 150         data[i]     = tmp1 + s;
 151         data[n-i-1] = tmp1 - s;
 152     }
 153
 154     ctx->rdft.rdft_calc(&ctx->rdft, data);
 155
 156     next     = data[1] * 0.5;
 157     data[1] *= -1;
 158
 159     for (i = n - 2; i >= 0; i -= 2) {
 160         float inr = data[i    ];
 161         float ini = data[i + 1];
 162         float c   = COS(ctx, n, i);
 163         float s   = SIN(ctx, n, i);
 164
 165         data[i]     = c * inr + s * ini;
 166         data[i + 1] = next;
 167
 168         next += s * inr - c * ini;
 169     }
 170 }
 171
 172 static void dct32_func(DCTContext *ctx, FFTSample *data)
 173 {
 174     ctx->dct32(data, data);
 175 }
 176
 177 av_cold int ff_dct_init(DCTContext *s, int nbits, enum DCTTransformType inverse)
 178 {
 179     int n = 1 << nbits;
 180     int i;
 181
 182     memset(s, 0, sizeof(*s));
 183
 184     s->nbits   = nbits;
 185     s->inverse = inverse;
 186
 187     if (inverse == DCT_II && nbits == 5) {
 188         s->dct_calc = dct32_func;
 189     } else {
 190         ff_init_ff_cos_tabs(nbits + 2);
 191
 192         s->costab = ff_cos_tabs[nbits + 2];
 193         s->csc2   = av_malloc_array(n / 2, sizeof(FFTSample));
 194
 195         if (ff_rdft_init(&s->rdft, nbits, inverse == DCT_III) < 0) {
 196             av_freep(&s->csc2);
 197             return -1;
 198         }
 199
 200         for (i = 0; i < n / 2; i++)
 201             s->csc2[i] = 0.5 / sin((M_PI / (2 * n) * (2 * i + 1)));
 202
 203         switch (inverse) {
 204         case DCT_I  : s->dct_calc = dct_calc_I_c;   break;
 205         case DCT_II : s->dct_calc = dct_calc_II_c;  break;
 206         case DCT_III: s->dct_calc = dct_calc_III_c; break;
 207         case DST_I  : s->dct_calc = dst_calc_I_c;   break;
 208         }
 209     }
 210
 211     s->dct32 = ff_dct32_float;
 212     if (ARCH_X86)
 213         ff_dct_init_x86(s);
 214
 215     return 0;
 216 }
 217
 218 av_cold void ff_dct_end(DCTContext *s)
 219 {
 220     ff_rdft_end(&s->rdft);
 221     av_freep(&s->csc2);
 222 }