1 files changed, 52 insertions, 24 deletions

diff --git a/src/pcm/PcmDither.cxx b/src/pcm/PcmDither.cxx
index 98d0d443e..7b2a9e900 100644
--- a/src/pcm/PcmDither.cxx
+++ b/src/pcm/PcmDither.cxx
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2003-2013 The Music Player Daemon Project
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * This program is free software; you can redistribute it and/or modify
@@ -20,18 +20,14 @@
 #include "config.h"
 #include "PcmDither.hxx"
 #include "PcmPrng.hxx"
+#include "Traits.hxx"
 
-inline int16_t
-PcmDither::Dither24To16(int_fast32_t sample)
+template<typename T, T MIN, T MAX, unsigned scale_bits>
+inline T
+PcmDither::Dither(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;
+	constexpr T round = 1 << (scale_bits - 1);
+	constexpr T mask = (1 << scale_bits) - 1;
 
 	sample += error[0] - error[1] + error[2];
 
@@ -39,9 +35,9 @@ PcmDither::Dither24To16(int_fast32_t sample)
 	error[1] = error[0] / 2;
 
 	/* round */
-	int_fast32_t output = sample + round;
+	T output = sample + round;
 
-	int_fast32_t rnd = pcm_prng(random);
+	const T rnd = pcm_prng(random);
 	output += (rnd & mask) - (random & mask);
 
 	random = rnd;
@@ -63,27 +59,59 @@ PcmDither::Dither24To16(int_fast32_t sample)
 
 	error[0] = sample - output;
 
-	return (int16_t)(output >> scale_bits);
+	return output >> scale_bits;
 }
 
-void
-PcmDither::Dither24To16(int16_t *dest, const int32_t *src,
-			const int32_t *src_end)
+template<typename ST, unsigned SBITS, unsigned DBITS>
+inline ST
+PcmDither::DitherShift(ST sample)
+{
+	static_assert(sizeof(ST) * 8 > SBITS, "Source type too small");
+	static_assert(SBITS > DBITS, "Non-positive scale_bits");
+
+	static constexpr ST MIN = -(ST(1) << (SBITS - 1));
+	static constexpr ST MAX = (ST(1) << (SBITS - 1)) - 1;
+
+	return Dither<ST, MIN, MAX, SBITS - DBITS>(sample);
+}
+
+template<typename ST, typename DT>
+inline typename DT::value_type
+PcmDither::DitherConvert(typename ST::value_type sample)
+{
+	static_assert(ST::BITS > DT::BITS,
+		      "Sample formats cannot be dithered");
+
+	constexpr unsigned scale_bits = ST::BITS - DT::BITS;
+
+	return Dither<typename ST::sum_type, ST::MIN, ST::MAX,
+		      scale_bits>(sample);
+}
+
+template<typename ST, typename DT>
+inline void
+PcmDither::DitherConvert(typename DT::pointer_type dest,
+			 typename ST::const_pointer_type src,
+			 typename ST::const_pointer_type src_end)
 {
 	while (src < src_end)
-		*dest++ = Dither24To16(*src++);
+		*dest++ = DitherConvert<ST, DT>(*src++);
 }
 
-inline int16_t
-PcmDither::Dither32To16(int_fast32_t sample)
+inline void
+PcmDither::Dither24To16(int16_t *dest, const int32_t *src,
+			const int32_t *src_end)
 {
-	return Dither24To16(sample >> 8);
+	typedef SampleTraits<SampleFormat::S24_P32> ST;
+	typedef SampleTraits<SampleFormat::S16> DT;
+	DitherConvert<ST, DT>(dest, src, src_end);
 }
 
-void
+inline void
 PcmDither::Dither32To16(int16_t *dest, const int32_t *src,
 			const int32_t *src_end)
 {
-	while (src < src_end)
-		*dest++ = Dither32To16(*src++);
+	typedef SampleTraits<SampleFormat::S32> ST;
+	typedef SampleTraits<SampleFormat::S16> DT;
+	DitherConvert<ST, DT>(dest, src, src_end);
 }