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/*
* Copyright 2023 jacqueline <me@jacqueline.id.au>
*
* SPDX-License-Identifier: GPL-3.0-only
*/
#pragma once
#include <stdint.h>
#include <algorithm>
#include <mad.h>
namespace sample {
// A signed, 16-bit PCM sample. All decoder output should be normalised to this
// format, in order to simplify resampling and/or re-encoding for bluetooth.
// Why 'only' 16 bits?
// 1. It's the lowest common bits per sample amongst our codecs. A higher bits
// per sample would require us to uselessly scale up those outputs.
// 2. With appropriate dithering, you're not going to hear a difference
// between 16 bit samples and higher bits anyway.
// 3. Monty from Xiph.org reckons it's all you need.
typedef int16_t Sample;
constexpr auto Clip(int64_t v) -> Sample {
return std::clamp<int64_t>(v, INT16_MIN, INT16_MAX);
}
auto shiftWithDither(int64_t src, uint_fast8_t bits) -> Sample;
constexpr auto FromSigned(int32_t src, uint_fast8_t bits) -> Sample {
if (bits > 16) {
return shiftWithDither(src, bits - 16);
} else if (bits < 16) {
return src << (sizeof(Sample) * 8 - bits);
}
return src;
}
constexpr auto FromUnsigned(uint32_t src, uint_fast8_t bits) -> Sample {
// Left-align, then substract the max value / 2 to make the sample centred
// around zero.
return (src << (sizeof(uint16_t) * 8 - bits)) - (~0UL >> 1);
}
constexpr auto FromFloat(float src) -> Sample {
int32_t quantised =
std::clamp<float>(src, -1.0f, 1.0f) * static_cast<float>(INT32_MAX);
return FromSigned(quantised, 32);
}
constexpr auto FromDouble(double src) -> Sample {
int32_t quantised =
std::clamp<double>(src, -1.0, 1.0) * static_cast<double>(INT32_MAX);
return FromSigned(quantised, 32);
}
constexpr auto FromMad(mad_fixed_t src) -> Sample {
// Round the bottom bits.
src += (1L << (MAD_F_FRACBITS - 24));
// Clip the leftover bits to within range.
if (src >= MAD_F_ONE)
src = MAD_F_ONE - 1;
else if (src < -MAD_F_ONE)
src = -MAD_F_ONE;
// Quantize.
return FromSigned(src >> (MAD_F_FRACBITS + 1 - 24), 24);
}
static constexpr float kFactor = 1.0f / static_cast<float>(INT16_MAX);
constexpr auto ToFloat(Sample src) -> float {
return src * kFactor;
}
} // namespace sample
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