suyu/src/audio_core/algorithm/interpolate.h

// Copyright 2018 yuzu Emulator Project
// Licensed under GPLv2 or any later version
// Refer to the license.txt file included.

#pragma once

#include <array>
#include <vector>
#include "audio_core/algorithm/filter.h"
#include "common/common_types.h"

namespace AudioCore {

struct InterpolationState {
    static constexpr size_t lanczos_taps = 4;
    static constexpr size_t history_size = lanczos_taps * 2 - 1;

    double current_ratio = 0.0;
    CascadingFilter nyquist;
    std::array<std::array<s16, 2>, history_size> history = {};
    double position = 0;
};

/// Interpolates input signal to produce output signal.
/// @param input The signal to interpolate.
/// @param ratio Interpolation ratio.
///              ratio > 1.0 results in fewer output samples.
///              ratio < 1.0 results in more output samples.
/// @returns Output signal.
std::vector<s16> Interpolate(InterpolationState& state, std::vector<s16> input, double ratio);

/// Interpolates input signal to produce output signal.
/// @param input The signal to interpolate.
/// @param input_rate The sample rate of input.
/// @param output_rate The desired sample rate of the output.
/// @returns Output signal.
inline std::vector<s16> Interpolate(InterpolationState& state, std::vector<s16> input,
                                    u32 input_rate, u32 output_rate) {
    const double ratio = static_cast<double>(input_rate) / static_cast<double>(output_rate);
    return Interpolate(state, std::move(input), ratio);
}

} // namespace AudioCore