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100 lines
2.3 KiB
C++
100 lines
2.3 KiB
C++
// SPDX-License-Identifier: GPL-2.0-or-later
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// Copyright The Music Player Daemon Project
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#include "Dither.hxx"
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#include "Prng.hxx"
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template<typename T, T MIN, T MAX, unsigned scale_bits>
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inline T
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PcmDither::Dither(T sample) noexcept
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{
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constexpr T round = 1 << (scale_bits - 1);
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constexpr T mask = (1 << scale_bits) - 1;
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sample += error[0] - error[1] + error[2];
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error[2] = error[1];
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error[1] = error[0] / 2;
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/* round */
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T output = sample + round;
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const T rnd = pcm_prng(random);
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output += (rnd & mask) - (random & mask);
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random = rnd;
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/* clip */
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if (output > MAX) {
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output = MAX;
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if (sample > MAX)
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sample = MAX;
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} else if (output < MIN) {
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output = MIN;
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if (sample < MIN)
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sample = MIN;
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}
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output &= ~mask;
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error[0] = sample - output;
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return output >> scale_bits;
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}
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template<typename ST, unsigned SBITS, unsigned DBITS>
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inline ST
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PcmDither::DitherShift(ST sample) noexcept
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{
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static_assert(sizeof(ST) * 8 > SBITS, "Source type too small");
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static_assert(SBITS > DBITS, "Non-positive scale_bits");
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static constexpr ST MIN = -(ST(1) << (SBITS - 1));
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static constexpr ST MAX = (ST(1) << (SBITS - 1)) - 1;
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return Dither<ST, MIN, MAX, SBITS - DBITS>(sample);
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}
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template<IntegerSampleTraits ST, IntegerSampleTraits DT>
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inline typename DT::value_type
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PcmDither::DitherConvert(typename ST::value_type sample) noexcept
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{
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static_assert(ST::BITS > DT::BITS,
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"Sample formats cannot be dithered");
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constexpr unsigned scale_bits = ST::BITS - DT::BITS;
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return Dither<typename ST::sum_type, ST::MIN, ST::MAX,
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scale_bits>(sample);
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}
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template<IntegerSampleTraits ST, IntegerSampleTraits DT>
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inline void
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PcmDither::DitherConvert(typename DT::pointer dest,
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typename ST::const_pointer src,
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typename ST::const_pointer src_end) noexcept
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{
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while (src < src_end)
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*dest++ = DitherConvert<ST, DT>(*src++);
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}
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inline void
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PcmDither::Dither24To16(int16_t *dest, const int32_t *src,
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const int32_t *src_end) noexcept
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{
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using ST = SampleTraits<SampleFormat::S24_P32>;
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using DT = SampleTraits<SampleFormat::S16>;
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DitherConvert<ST, DT>(dest, src, src_end);
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}
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inline void
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PcmDither::Dither32To16(int16_t *dest, const int32_t *src,
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const int32_t *src_end) noexcept
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{
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using ST = SampleTraits<SampleFormat::S32>;
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using DT = SampleTraits<SampleFormat::S16>;
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DitherConvert<ST, DT>(dest, src, src_end);
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}
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