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-rw-r--r--src/pcm/PcmDither.cxx89
1 files changed, 89 insertions, 0 deletions
diff --git a/src/pcm/PcmDither.cxx b/src/pcm/PcmDither.cxx
new file mode 100644
index 000000000..98d0d443e
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+++ b/src/pcm/PcmDither.cxx
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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++);
+}