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/*
* 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++);
}
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