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88 lines
3.0 KiB
C++
88 lines
3.0 KiB
C++
//
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// WaveformGenerator.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 03/05/2020.
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// Copyright © 2020 Thomas Harte. All rights reserved.
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//
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#pragma once
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#include "Tables.hpp"
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#include "LowFrequencyOscillator.hpp"
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namespace Yamaha::OPL {
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enum class Waveform {
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Sine, HalfSine, AbsSine, PulseSine
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};
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template <int phase_precision> class WaveformGenerator {
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public:
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/*!
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@returns The output of waveform @c form at [integral] phase @c phase.
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*/
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static constexpr LogSign wave(Waveform form, int phase) {
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constexpr int waveforms[4][4] = {
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{1023, 1023, 1023, 1023}, // Sine: don't mask in any quadrant.
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{511, 511, 0, 0}, // Half sine: keep the first half intact, lock to 0 in the second half.
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{511, 511, 511, 511}, // AbsSine: endlessly repeat the first half of the sine wave.
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{255, 0, 255, 0}, // PulseSine: act as if the first quadrant is in the first and third; lock the other two to 0.
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};
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return negative_log_sin(phase & waveforms[int(form)][(phase >> 8) & 3]);
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}
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/*!
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@returns The output of waveform @c form at [scaled] phase @c scaled_phase given the modulation input @c modulation.
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*/
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static constexpr LogSign wave(Waveform form, int scaled_phase, LogSign modulation) {
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const int scaled_phase_offset = modulation.level(phase_precision);
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const int phase = (scaled_phase + scaled_phase_offset) >> phase_precision;
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return wave(form, phase);
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}
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/*!
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@returns Snare output, calculated from the current LFSR state as captured in @c oscillator and an operator's phase.
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*/
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static constexpr LogSign snare(const LowFrequencyOscillator &oscillator, int phase) {
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// If noise is 0, output is positive.
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// If noise is 1, output is negative.
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// If (noise ^ sign) is 0, output is 0. Otherwise it is max.
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const int sign = phase & 0x200;
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const int level = ((phase >> 9) & 1) ^ oscillator.lfsr;
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return negative_log_sin(sign + (level << 8));
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}
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/*!
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@returns Cymbal output, calculated from an operator's phase and a modulator's phase.
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*/
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static constexpr LogSign cymbal(int carrier_phase, int modulator_phase) {
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return negative_log_sin(256 + (phase_combination(carrier_phase, modulator_phase) << 9));
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}
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/*!
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@returns High-hat output, calculated from the current LFSR state as captured in @c oscillator, an operator's phase and a modulator's phase.
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*/
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static constexpr LogSign high_hat(const LowFrequencyOscillator &oscillator, int carrier_phase, int modulator_phase) {
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constexpr int angles[] = {0x234, 0xd0, 0x2d0, 0x34};
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return negative_log_sin(angles[
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phase_combination(carrier_phase, modulator_phase) |
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(oscillator.lfsr << 1)
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]);
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}
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private:
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/*!
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@returns The phase bit used for cymbal and high-hat generation, which is a function of two operators' phases.
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*/
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static constexpr int phase_combination(int carrier_phase, int modulator_phase) {
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return (
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((carrier_phase >> 5) ^ (carrier_phase >> 3)) &
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((modulator_phase >> 7) ^ (modulator_phase >> 2)) &
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((carrier_phase >> 5) ^ (modulator_phase >> 3))
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) & 1;
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}
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};
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}
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