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  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
  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. }
  124.