content: /*
   * 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();
      }
  
  }
  