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