86 lines
2.8 KiB
C++
86 lines
2.8 KiB
C++
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// Copyright 2016 Citra Emulator Project
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// Licensed under GPLv2 or any later version
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// Refer to the license.txt file included.
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#include "audio_core/interpolate.h"
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#include "common/assert.h"
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#include "common/math_util.h"
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namespace AudioInterp {
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// Calculations are done in fixed point with 24 fractional bits.
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// (This is not verified. This was chosen for minimal error.)
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constexpr u64 scale_factor = 1 << 24;
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constexpr u64 scale_mask = scale_factor - 1;
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/// Here we step over the input in steps of rate_multiplier, until we consume all of the input.
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/// Three adjacent samples are passed to fn each step.
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template <typename Function>
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static StereoBuffer16 StepOverSamples(State& state, const StereoBuffer16& input, float rate_multiplier, Function fn) {
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ASSERT(rate_multiplier > 0);
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if (input.size() < 2)
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return {};
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StereoBuffer16 output;
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output.reserve(static_cast<size_t>(input.size() / rate_multiplier));
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u64 step_size = static_cast<u64>(rate_multiplier * scale_factor);
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u64 fposition = 0;
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const u64 max_fposition = input.size() * scale_factor;
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while (fposition < 1 * scale_factor) {
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u64 fraction = fposition & scale_mask;
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output.push_back(fn(fraction, state.xn2, state.xn1, input[0]));
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fposition += step_size;
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}
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while (fposition < 2 * scale_factor) {
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u64 fraction = fposition & scale_mask;
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output.push_back(fn(fraction, state.xn1, input[0], input[1]));
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fposition += step_size;
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}
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while (fposition < max_fposition) {
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u64 fraction = fposition & scale_mask;
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size_t index = static_cast<size_t>(fposition / scale_factor);
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output.push_back(fn(fraction, input[index - 2], input[index - 1], input[index]));
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fposition += step_size;
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}
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state.xn2 = input[input.size() - 2];
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state.xn1 = input[input.size() - 1];
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return output;
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}
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StereoBuffer16 None(State& state, const StereoBuffer16& input, float rate_multiplier) {
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return StepOverSamples(state, input, rate_multiplier, [](u64 fraction, const auto& x0, const auto& x1, const auto& x2) {
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return x0;
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});
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}
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StereoBuffer16 Linear(State& state, const StereoBuffer16& input, float rate_multiplier) {
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// Note on accuracy: Some values that this produces are +/- 1 from the actual firmware.
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return StepOverSamples(state, input, rate_multiplier, [](u64 fraction, const auto& x0, const auto& x1, const auto& x2) {
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// This is a saturated subtraction. (Verified by black-box fuzzing.)
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s64 delta0 = MathUtil::Clamp<s64>(x1[0] - x0[0], -32768, 32767);
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s64 delta1 = MathUtil::Clamp<s64>(x1[1] - x0[1], -32768, 32767);
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return std::array<s16, 2> {
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static_cast<s16>(x0[0] + fraction * delta0 / scale_factor),
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static_cast<s16>(x0[1] + fraction * delta1 / scale_factor)
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};
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});
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}
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} // namespace AudioInterp
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