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-rw-r--r-- | libavcodec/dctref.c | 121 |
1 files changed, 121 insertions, 0 deletions
diff --git a/libavcodec/dctref.c b/libavcodec/dctref.c new file mode 100644 index 0000000000..faad057a9a --- /dev/null +++ b/libavcodec/dctref.c @@ -0,0 +1,121 @@ +/* + * reference discrete cosine transform (double precision) + * Copyright (C) 2009 Dylan Yudaken + * + * This file is part of FFmpeg. + * + * FFmpeg is free software; you can redistribute it and/or + * modify it under the terms of the GNU Lesser General Public + * License as published by the Free Software Foundation; either + * version 2.1 of the License, or (at your option) any later version. + * + * FFmpeg is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public + * License along with FFmpeg; if not, write to the Free Software + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA + */ + +/** + * @file libavcodec/dctref.c + * reference discrete cosine transform (double precision) + * + * @author Dylan Yudaken (dyudaken at gmail) + * + * @note This file could be optimized a lot, but is for + * reference and so readability is better. + */ + +#include "libavutil/mathematics.h" +static double coefficients[8 * 8]; + +/** + * Initialize the double precision discrete cosine transform + * functions fdct & idct. + */ +av_cold void ff_ref_dct_init(void) +{ + unsigned int i, j; + + for (j = 0; j < 8; ++j) { + coefficients[j] = sqrt(0.125); + for (i = 8; i < 64; i += 8) { + coefficients[i + j] = 0.5 * cos(i * (j + 0.5) * M_PI / 64.0); + } + } +} + +/** + * Transform 8x8 block of data with a double precision forward DCT <br> + * This is a reference implementation. + * + * @param block pointer to 8x8 block of data to transform + */ +void ff_ref_fdct(short *block) +{ + /* implement the equation: block = coefficients * block * coefficients' */ + + unsigned int i, j, k; + double out[8 * 8]; + + /* out = coefficients * block */ + for (i = 0; i < 64; i += 8) { + for (j = 0; j < 8; ++j) { + double tmp = 0; + for (k = 0; k < 8; ++k) { + tmp += coefficients[i + k] * block[k * 8 + j]; + } + out[i + j] = tmp * 8; + } + } + + /* block = out * (coefficients') */ + for (j = 0; j < 8; ++j) { + for (i = 0; i < 64; i += 8) { + double tmp = 0; + for (k = 0; k < 8; ++k) { + tmp += out[i + k] * coefficients[j * 8 + k]; + } + block[i + j] = floor(tmp + 0.499999999999); + } + } +} + +/** + * Transform 8x8 block of data with a double precision inverse DCT <br> + * This is a reference implementation. + * + * @param block pointer to 8x8 block of data to transform + */ +void ff_ref_idct(short *block) +{ + /* implement the equation: block = (coefficients') * block * coefficients */ + + unsigned int i, j, k; + double out[8 * 8]; + + /* out = block * coefficients */ + for (i = 0; i < 64; i += 8) { + for (j = 0; j < 8; ++j) { + double tmp = 0; + for (k = 0; k < 8; ++k) { + tmp += block[i + k] * coefficients[k * 8 + j]; + } + out[i + j] = tmp; + } + } + + /* block = (coefficients') * out */ + for (i = 0; i < 8; ++i) { + for (j = 0; j < 8; ++j) { + double tmp = 0; + for (k = 0; k < 64; k += 8) { + tmp += coefficients[k + i] * out[k + j]; + } + block[i * 8 + j] = floor(tmp + 0.5); + } + } +} |