| /* |
| * Copyright (C) 2015 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package com.example.android.common.midi.synth; |
| |
| /** |
| * Sinewave oscillator. |
| */ |
| public class SineOscillator extends SawOscillator { |
| // Factorial constants. |
| private static final float IF3 = 1.0f / (2 * 3); |
| private static final float IF5 = IF3 / (4 * 5); |
| private static final float IF7 = IF5 / (6 * 7); |
| private static final float IF9 = IF7 / (8 * 9); |
| private static final float IF11 = IF9 / (10 * 11); |
| |
| /** |
| * Calculate sine using Taylor expansion. Do not use values outside the range. |
| * |
| * @param currentPhase in the range of -1.0 to +1.0 for one cycle |
| */ |
| public static float fastSin(float currentPhase) { |
| |
| /* Wrap phase back into region where results are more accurate. */ |
| float yp = (currentPhase > 0.5f) ? 1.0f - currentPhase |
| : ((currentPhase < (-0.5f)) ? (-1.0f) - currentPhase : currentPhase); |
| |
| float x = (float) (yp * Math.PI); |
| float x2 = (x * x); |
| /* Taylor expansion out to x**11/11! factored into multiply-adds */ |
| return x * (x2 * (x2 * (x2 * (x2 * ((x2 * (-IF11)) + IF9) - IF7) + IF5) - IF3) + 1); |
| } |
| |
| @Override |
| public float render() { |
| // Convert raw sawtooth to sine. |
| float phase = incrementWrapPhase(); |
| return fastSin(phase) * getAmplitude(); |
| } |
| |
| } |