libavcodec/dctref.c

   1 /*
   2  * reference discrete cosine transform (double precision)
   3  * Copyright (C) 2009 Dylan Yudaken
   4  *
   5  * This file is part of FFmpeg.
   6  *
   7  * FFmpeg is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2.1 of the License, or (at your option) any later version.
  11  *
  12  * FFmpeg is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with FFmpeg; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20  */
  21
  22 /**
  23  * @file libavcodec/dctref.c
  24  * reference discrete cosine transform (double precision)
  25  *
  26  * @author Dylan Yudaken (dyudaken at gmail)
  27  *
  28  * @note This file could be optimized a lot, but is for
  29  * reference and so readability is better.
  30  */
  31
  32 #include "libavutil/mathematics.h"
  33 static double coefficients[8 * 8];
  34
  35 /**
  36  * Initialize the double precision discrete cosine transform
  37  * functions fdct & idct.
  38  */
  39 av_cold void ff_ref_dct_init(void)
  40 {
  41     unsigned int i, j;
  42
  43     for (j = 0; j < 8; ++j) {
  44         coefficients[j] = sqrt(0.125);
  45         for (i = 8; i < 64; i += 8) {
  46             coefficients[i + j] = 0.5 * cos(i * (j + 0.5) * M_PI / 64.0);
  47         }
  48     }
  49 }
  50
  51 /**
  52  * Transform 8x8 block of data with a double precision forward DCT <br>
  53  * This is a reference implementation.
  54  *
  55  * @param block pointer to 8x8 block of data to transform
  56  */
  57 void ff_ref_fdct(short *block)
  58 {
  59     /* implement the equation: block = coefficients * block * coefficients' */
  60
  61     unsigned int i, j, k;
  62     double out[8 * 8];
  63
  64     /* out = coefficients * block */
  65     for (i = 0; i < 64; i += 8) {
  66         for (j = 0; j < 8; ++j) {
  67             double tmp = 0;
  68             for (k = 0; k < 8; ++k) {
  69                 tmp += coefficients[i + k] * block[k * 8 + j];
  70             }
  71             out[i + j] = tmp * 8;
  72         }
  73     }
  74
  75     /* block = out * (coefficients') */
  76     for (j = 0; j < 8; ++j) {
  77         for (i = 0; i < 64; i += 8) {
  78             double tmp = 0;
  79             for (k = 0; k < 8; ++k) {
  80                 tmp += out[i + k] * coefficients[j * 8 + k];
  81             }
  82             block[i + j] = floor(tmp + 0.499999999999);
  83         }
  84     }
  85 }
  86
  87 /**
  88  * Transform 8x8 block of data with a double precision inverse DCT <br>
  89  * This is a reference implementation.
  90  *
  91  * @param block pointer to 8x8 block of data to transform
  92  */
  93 void ff_ref_idct(short *block)
  94 {
  95     /* implement the equation: block = (coefficients') * block * coefficients */
  96
  97     unsigned int i, j, k;
  98     double out[8 * 8];
  99
 100     /* out = block * coefficients */
 101     for (i = 0; i < 64; i += 8) {
 102         for (j = 0; j < 8; ++j) {
 103             double tmp = 0;
 104             for (k = 0; k < 8; ++k) {
 105                 tmp += block[i + k] * coefficients[k * 8 + j];
 106             }
 107             out[i + j] = tmp;
 108         }
 109     }
 110
 111     /* block = (coefficients') * out */
 112     for (i = 0; i < 8; ++i) {
 113         for (j = 0; j < 8; ++j) {
 114             double tmp = 0;
 115             for (k = 0; k < 64; k += 8) {
 116                 tmp += coefficients[k + i] * out[k + j];
 117             }
 118             block[i * 8 + j] = floor(tmp + 0.5);
 119         }
 120     }
 121 }