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// Copyright 2018 yuzu Emulator Project
// Licensed under GPLv2 or any later version
// Refer to the license.txt file included.
#define _USE_MATH_DEFINES
#include <algorithm>
#include <cmath>
#include <vector>
#include "audio_core/algorithm/interpolate.h"
#include "common/common_types.h"
#include "common/logging/log.h"
namespace AudioCore {
/// The Lanczos kernel
static double Lanczos(std::size_t a, double x) {
if (x == 0.0)
return 1.0;
const double px = M_PI * x;
return a * std::sin(px) * std::sin(px / a) / (px * px);
}
std::vector<s16> Interpolate(InterpolationState& state, std::vector<s16> input, double ratio) {
if (input.size() < 2)
return {};
if (ratio <= 0) {
LOG_CRITICAL(Audio, "Nonsensical interpolation ratio {}", ratio);
ratio = 1.0;
}
if (ratio != state.current_ratio) {
const double cutoff_frequency = std::min(0.5 / ratio, 0.5 * ratio);
state.nyquist = CascadingFilter::LowPass(std::clamp(cutoff_frequency, 0.0, 0.4), 3);
state.current_ratio = ratio;
}
state.nyquist.Process(input);
constexpr std::size_t taps = InterpolationState::lanczos_taps;
const std::size_t num_frames = input.size() / 2;
std::vector<s16> output;
output.reserve(static_cast<std::size_t>(input.size() / ratio + 4));
double& pos = state.position;
auto& h = state.history;
for (std::size_t i = 0; i < num_frames; ++i) {
std::rotate(h.begin(), h.end() - 1, h.end());
h[0][0] = input[i * 2 + 0];
h[0][1] = input[i * 2 + 1];
while (pos <= 1.0) {
double l = 0.0;
double r = 0.0;
for (std::size_t j = 0; j < h.size(); j++) {
const double lanczos_calc = Lanczos(taps, pos + j - taps + 1);
l += lanczos_calc * h[j][0];
r += lanczos_calc * h[j][1];
}
output.emplace_back(static_cast<s16>(std::clamp(l, -32768.0, 32767.0)));
output.emplace_back(static_cast<s16>(std::clamp(r, -32768.0, 32767.0)));
pos += ratio;
}
pos -= 1.0;
}
return output;
}
} // namespace AudioCore
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