1 // Copyright 2014 Emilie Gillet. 2 // 3 // Author: Emilie Gillet (emilie.o.gillet@gmail.com) 4 // 5 // Permission is hereby granted, free of charge, to any person obtaining a copy 6 // of this software and associated documentation files (the "Software"), to deal 7 // in the Software without restriction, including without limitation the rights 8 // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 9 // copies of the Software, and to permit persons to whom the Software is 10 // furnished to do so, subject to the following conditions: 11 // 12 // The above copyright notice and this permission notice shall be included in 13 // all copies or substantial portions of the Software. 14 // 15 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 16 // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 17 // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 18 // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 19 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 20 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN 21 // THE SOFTWARE. 22 // 23 // See http://creativecommons.org/licenses/MIT/ for more information. 24 // 25 // ----------------------------------------------------------------------------- 26 // 27 // Cosine oscillator. Generates a cosine between 0.0 and 1.0 with minimal 28 // CPU use. 29 30 #ifndef STMLIB_DSP_COSINE_OSCILLATOR_H_ 31 #define STMLIB_DSP_COSINE_OSCILLATOR_H_ 32 33 #include "stmlib/stmlib.h" 34 35 #include <cmath> 36 37 namespace stmlib { 38 39 enum CosineOscillatorMode { 40 COSINE_OSCILLATOR_APPROXIMATE, 41 COSINE_OSCILLATOR_EXACT 42 }; 43 44 class CosineOscillator { 45 public: 46 CosineOscillator() { } 47 ~CosineOscillator() { } 48 49 template<CosineOscillatorMode mode> 50 inline void Init(float frequency) { 51 if (mode == COSINE_OSCILLATOR_APPROXIMATE) { 52 InitApproximate(frequency); 53 } else { 54 iir_coefficient_ = 2.0f * cosf(2.0f * M_PI * frequency); 55 initial_amplitude_ = iir_coefficient_ * 0.25f; 56 } 57 Start(); 58 } 59 60 inline void InitApproximate(float frequency) { 61 float sign = 16.0f; 62 frequency -= 0.25f; 63 if (frequency < 0.0f) { 64 frequency = -frequency; 65 } else { 66 if (frequency > 0.5f) { 67 frequency -= 0.5f; 68 } else { 69 sign = -16.0f; 70 } 71 } 72 iir_coefficient_ = sign * frequency * (1.0f - 2.0f * frequency); 73 initial_amplitude_ = iir_coefficient_ * 0.25f; 74 } 75 76 inline void Start() { 77 y1_ = initial_amplitude_; 78 y0_ = 0.5f; 79 } 80 81 inline float value() const { 82 return y1_ + 0.5f; 83 } 84 85 inline float Next() { 86 float temp = y0_; 87 y0_ = iir_coefficient_ * y0_ - y1_; 88 y1_ = temp; 89 return temp + 0.5f; 90 } 91 92 private: 93 float y1_; 94 float y0_; 95 float iir_coefficient_; 96 float initial_amplitude_; 97 98 DISALLOW_COPY_AND_ASSIGN(CosineOscillator); 99 }; 100 101 } // namespace stmlib 102 103 #endif // STMLIB_DSP_COSINE_OSCILLATOR_H_ 104