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
--- /dev/null
+++ b/src/pcm/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++);
+}