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Diffstat (limited to '')
-rw-r--r-- | src/PcmDither.cxx | 89 |
1 files changed, 89 insertions, 0 deletions
diff --git a/src/PcmDither.cxx b/src/PcmDither.cxx new file mode 100644 index 000000000..98d0d443e --- /dev/null +++ b/src/PcmDither.cxx @@ -0,0 +1,89 @@ +/* + * Copyright (C) 2003-2013 The Music Player Daemon Project + * http://www.musicpd.org + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program 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 General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. + */ + +#include "config.h" +#include "PcmDither.hxx" +#include "PcmPrng.hxx" + +inline int16_t +PcmDither::Dither24To16(int_fast32_t sample) +{ + constexpr unsigned from_bits = 24; + constexpr unsigned to_bits = 16; + constexpr unsigned scale_bits = from_bits - to_bits; + constexpr int_fast32_t round = 1 << (scale_bits - 1); + constexpr int_fast32_t mask = (1 << scale_bits) - 1; + constexpr int_fast32_t ONE = 1 << (from_bits - 1); + constexpr int_fast32_t MIN = -ONE; + constexpr int_fast32_t MAX = ONE - 1; + + sample += error[0] - error[1] + error[2]; + + error[2] = error[1]; + error[1] = error[0] / 2; + + /* round */ + int_fast32_t output = sample + round; + + int_fast32_t rnd = pcm_prng(random); + output += (rnd & mask) - (random & mask); + + random = rnd; + + /* clip */ + if (output > MAX) { + output = MAX; + + if (sample > MAX) + sample = MAX; + } else if (output < MIN) { + output = MIN; + + if (sample < MIN) + sample = MIN; + } + + output &= ~mask; + + error[0] = sample - output; + + return (int16_t)(output >> scale_bits); +} + +void +PcmDither::Dither24To16(int16_t *dest, const int32_t *src, + const int32_t *src_end) +{ + while (src < src_end) + *dest++ = Dither24To16(*src++); +} + +inline int16_t +PcmDither::Dither32To16(int_fast32_t sample) +{ + return Dither24To16(sample >> 8); +} + +void +PcmDither::Dither32To16(int16_t *dest, const int32_t *src, + const int32_t *src_end) +{ + while (src < src_end) + *dest++ = Dither32To16(*src++); +} |