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pcm/Dither: generic sample dithering using template

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This commit is contained in:
Max Kellermann 2013-12-22 16:09:07 +01:00
parent 32b834aa04
commit 4043f320fe
2 changed files with 25 additions and 13 deletions
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35
src/pcm/PcmDither.cxx
View File

@ -21,17 +21,12 @@
#include "PcmDither.hxx"
#include "PcmPrng.hxx"
inline int16_t
PcmDither::Dither24To16(int_fast32_t sample)
template<typename T, T MIN, T MAX, unsigned scale_bits>
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 +34,9 @@ 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;
@ -63,7 +58,21 @@ PcmDither::Dither24To16(int_fast32_t sample)
error[0] = sample - output;
return (int16_t)(output >> scale_bits);
return output;
}
inline int16_t
PcmDither::Dither24To16(int_fast32_t sample)
{
typedef decltype(sample) T;
constexpr unsigned from_bits = 24;
constexpr unsigned to_bits = 16;
constexpr unsigned scale_bits = from_bits - to_bits;
constexpr int_fast32_t ONE = 1 << (from_bits - 1);
constexpr int_fast32_t MIN = -ONE;
constexpr int_fast32_t MAX = ONE - 1;
return Dither<T, MIN, MAX, scale_bits>(sample) >> scale_bits;
}
void

3
src/pcm/PcmDither.hxx
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@ -30,6 +30,9 @@ public:
constexpr PcmDither()
:error{0, 0, 0}, random(0) {}
template<typename T, T MIN, T MAX, unsigned scale_bits>
T Dither(T sample);
void Dither24To16(int16_t *dest, const int32_t *src,
const int32_t *src_end);