93 lines
2.4 KiB
C++
93 lines
2.4 KiB
C++
/* SPDX-License-Identifier: BSD-3-Clause */
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/* SPDX-FileCopyrightText: OpenMPT Project Developers and Contributors */
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#pragma once
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#include "openmpt/all/BuildSettings.hpp"
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#include "mpt/base/macros.hpp"
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#include "mpt/random/engine.hpp"
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#include "mpt/random/default_engines.hpp"
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#include "mpt/random/random.hpp"
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#include "openmpt/base/Types.hpp"
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#include "openmpt/soundbase/MixSample.hpp"
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#include "openmpt/soundbase/MixSampleConvert.hpp"
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OPENMPT_NAMESPACE_BEGIN
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template <int ditherdepth = 1, bool triangular = false, bool shaped = true>
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struct Dither_SimpleImpl
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{
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public:
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using prng_type = mpt::fast_engine;
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template <typename Trd>
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static prng_type prng_init(Trd &rd)
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{
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return mpt::make_prng<prng_type>(rd);
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}
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private:
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int32 error = 0;
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public:
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template <uint32 targetbits, typename Trng>
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MPT_FORCEINLINE MixSampleInt process(MixSampleInt sample, Trng &prng)
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{
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if constexpr(targetbits == 0)
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{
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MPT_UNUSED(prng);
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return sample;
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} else
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{
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static_assert(sizeof(MixSampleInt) == 4);
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constexpr int rshift = (32 - targetbits) - MixSampleIntTraits::mix_headroom_bits;
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if constexpr(rshift <= 1)
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{
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MPT_UNUSED(prng);
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// nothing to dither
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return sample;
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} else
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{
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constexpr int rshiftpositive = (rshift > 1) ? rshift : 1; // work-around warnings about negative shift with C++14 compilers
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constexpr int round_mask = ~((1 << rshiftpositive) - 1);
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constexpr int round_offset = 1 << (rshiftpositive - 1);
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constexpr int noise_bits = rshiftpositive + (ditherdepth - 1);
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constexpr int noise_bias = (1 << (noise_bits - 1));
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int32 e = error;
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unsigned int unoise = 0;
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if constexpr(triangular)
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{
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unoise = (mpt::random<unsigned int>(prng, noise_bits) + mpt::random<unsigned int>(prng, noise_bits)) >> 1;
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} else
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{
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unoise = mpt::random<unsigned int>(prng, noise_bits);
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}
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int noise = static_cast<int>(unoise) - noise_bias; // un-bias
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int val = sample;
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if constexpr(shaped)
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{
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val += (e >> 1);
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}
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int rounded = (val + noise + round_offset) & round_mask;
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e = val - rounded;
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sample = rounded;
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error = e;
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return sample;
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}
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}
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}
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template <uint32 targetbits, typename Trng>
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MPT_FORCEINLINE MixSampleFloat process(MixSampleFloat sample, Trng &prng)
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{
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return mix_sample_cast<MixSampleFloat>(process<targetbits>(mix_sample_cast<MixSampleInt>(sample), prng));
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}
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};
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using Dither_Simple = Dither_SimpleImpl<>;
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OPENMPT_NAMESPACE_END
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