libavcodec/dctref.c

   1 /*
   2  * reference discrete cosine transform (double precision)
   3  * Copyright (C) 2009 Dylan Yudaken
   4  *
   5  * This file is part of Libav.
   6  *
   7  * Libav 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  * Libav 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 Libav; 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
  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 #include "dctref.h"
  34
  35 static double coefficients[8 * 8];
  36
  37 /**
  38  * Initialize the double precision discrete cosine transform
  39  * functions fdct & idct.
  40  */
  41 av_cold void ff_ref_dct_init(void)
  42 {
  43     unsigned int i, j;
  44
  45     for (j = 0; j < 8; ++j) {
  46         coefficients[j] = sqrt(0.125);
  47         for (i = 8; i < 64; i += 8) {
  48             coefficients[i + j] = 0.5 * cos(i * (j + 0.5) * M_PI / 64.0);
  49         }
  50     }
  51 }
  52
  53 /**
  54  * Transform 8x8 block of data with a double precision forward DCT <br>
  55  * This is a reference implementation.
  56  *
  57  * @param block pointer to 8x8 block of data to transform
  58  */
  59 void ff_ref_fdct(short *block)
  60 {
  61     /* implement the equation: block = coefficients * block * coefficients' */
  62
  63     unsigned int i, j, k;
  64     double out[8 * 8];
  65
  66     /* out = coefficients * block */
  67     for (i = 0; i < 64; i += 8) {
  68         for (j = 0; j < 8; ++j) {
  69             double tmp = 0;
  70             for (k = 0; k < 8; ++k) {
  71                 tmp += coefficients[i + k] * block[k * 8 + j];
  72             }
  73             out[i + j] = tmp * 8;
  74         }
  75     }
  76
  77     /* block = out * (coefficients') */
  78     for (j = 0; j < 8; ++j) {
  79         for (i = 0; i < 64; i += 8) {
  80             double tmp = 0;
  81             for (k = 0; k < 8; ++k) {
  82                 tmp += out[i + k] * coefficients[j * 8 + k];
  83             }
  84             block[i + j] = floor(tmp + 0.499999999999);
  85         }
  86     }
  87 }
  88
  89 /**
  90  * Transform 8x8 block of data with a double precision inverse DCT <br>
  91  * This is a reference implementation.
  92  *
  93  * @param block pointer to 8x8 block of data to transform
  94  */
  95 void ff_ref_idct(short *block)
  96 {
  97     /* implement the equation: block = (coefficients') * block * coefficients */
  98
  99     unsigned int i, j, k;
 100     double out[8 * 8];
 101
 102     /* out = block * coefficients */
 103     for (i = 0; i < 64; i += 8) {
 104         for (j = 0; j < 8; ++j) {
 105             double tmp = 0;
 106             for (k = 0; k < 8; ++k) {
 107                 tmp += block[i + k] * coefficients[k * 8 + j];
 108             }
 109             out[i + j] = tmp;
 110         }
 111     }
 112
 113     /* block = (coefficients') * out */
 114     for (i = 0; i < 8; ++i) {
 115         for (j = 0; j < 8; ++j) {
 116             double tmp = 0;
 117             for (k = 0; k < 64; k += 8) {
 118                 tmp += coefficients[k + i] * out[k + j];
 119             }
 120             block[i * 8 + j] = floor(tmp + 0.5);
 121         }
 122     }
 123 }