1 /* 2 * Copyright (C) 2015 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.example.android.common.midi.synth; 18 19 /** 20 * Sinewave oscillator. 21 */ 22 public class SineOscillator extends SawOscillator { 23 // Factorial constants. 24 private static final float IF3 = 1.0f / (2 * 3); 25 private static final float IF5 = IF3 / (4 * 5); 26 private static final float IF7 = IF5 / (6 * 7); 27 private static final float IF9 = IF7 / (8 * 9); 28 private static final float IF11 = IF9 / (10 * 11); 29 30 /** 31 * Calculate sine using Taylor expansion. Do not use values outside the range. 32 * 33 * @param currentPhase in the range of -1.0 to +1.0 for one cycle 34 */ 35 public static float fastSin(float currentPhase) { 36 37 /* Wrap phase back into region where results are more accurate. */ 38 float yp = (currentPhase > 0.5f) ? 1.0f - currentPhase 39 : ((currentPhase < (-0.5f)) ? (-1.0f) - currentPhase : currentPhase); 40 41 float x = (float) (yp * Math.PI); 42 float x2 = (x * x); 43 /* Taylor expansion out to x**11/11! factored into multiply-adds */ 44 return x * (x2 * (x2 * (x2 * (x2 * ((x2 * (-IF11)) + IF9) - IF7) + IF5) - IF3) + 1); 45 } 46 47 @Override 48 public float render() { 49 // Convert raw sawtooth to sine. 50 float phase = incrementWrapPhase(); 51 return fastSin(phase) * getAmplitude(); 52 } 53 54 } 55
