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libavcodec/dctref.c

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00001 /*
00002  * reference discrete cosine transform (double precision)
00003  * Copyright (C) 2009 Dylan Yudaken
00004  *
00005  * This file is part of FFmpeg.
00006  *
00007  * FFmpeg is free software; you can redistribute it and/or
00008  * modify it under the terms of the GNU Lesser General Public
00009  * License as published by the Free Software Foundation; either
00010  * version 2.1 of the License, or (at your option) any later version.
00011  *
00012  * FFmpeg is distributed in the hope that it will be useful,
00013  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00014  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00015  * Lesser General Public License for more details.
00016  *
00017  * You should have received a copy of the GNU Lesser General Public
00018  * License along with FFmpeg; if not, write to the Free Software
00019  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
00020  */
00021 
00032 #include "libavutil/mathematics.h"
00033 #include "dctref.h"
00034 
00035 static double coefficients[8 * 8];
00036 
00041 av_cold void ff_ref_dct_init(void)
00042 {
00043     unsigned int i, j;
00044 
00045     for (j = 0; j < 8; ++j) {
00046         coefficients[j] = sqrt(0.125);
00047         for (i = 8; i < 64; i += 8) {
00048             coefficients[i + j] = 0.5 * cos(i * (j + 0.5) * M_PI / 64.0);
00049         }
00050     }
00051 }
00052 
00059 void ff_ref_fdct(short *block)
00060 {
00061     /* implement the equation: block = coefficients * block * coefficients' */
00062 
00063     unsigned int i, j, k;
00064     double out[8 * 8];
00065 
00066     /* out = coefficients * block */
00067     for (i = 0; i < 64; i += 8) {
00068         for (j = 0; j < 8; ++j) {
00069             double tmp = 0;
00070             for (k = 0; k < 8; ++k) {
00071                 tmp += coefficients[i + k] * block[k * 8 + j];
00072             }
00073             out[i + j] = tmp * 8;
00074         }
00075     }
00076 
00077     /* block = out * (coefficients') */
00078     for (j = 0; j < 8; ++j) {
00079         for (i = 0; i < 64; i += 8) {
00080             double tmp = 0;
00081             for (k = 0; k < 8; ++k) {
00082                 tmp += out[i + k] * coefficients[j * 8 + k];
00083             }
00084             block[i + j] = floor(tmp + 0.499999999999);
00085         }
00086     }
00087 }
00088 
00095 void ff_ref_idct(short *block)
00096 {
00097     /* implement the equation: block = (coefficients') * block * coefficients */
00098 
00099     unsigned int i, j, k;
00100     double out[8 * 8];
00101 
00102     /* out = block * coefficients */
00103     for (i = 0; i < 64; i += 8) {
00104         for (j = 0; j < 8; ++j) {
00105             double tmp = 0;
00106             for (k = 0; k < 8; ++k) {
00107                 tmp += block[i + k] * coefficients[k * 8 + j];
00108             }
00109             out[i + j] = tmp;
00110         }
00111     }
00112 
00113     /* block = (coefficients') * out */
00114     for (i = 0; i < 8; ++i) {
00115         for (j = 0; j < 8; ++j) {
00116             double tmp = 0;
00117             for (k = 0; k < 64; k += 8) {
00118                 tmp += coefficients[k + i] * out[k + j];
00119             }
00120             block[i * 8 + j] = floor(tmp + 0.5);
00121         }
00122     }
00123 }

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