webrtc / src / 63fb95a68d70cd7036db65c3378e91cb77faa44d / . / webrtc / modules / audio_coding / codecs / ilbc / lsf_to_lsp.c

/* | |

* Copyright (c) 2011 The WebRTC project authors. All Rights Reserved. | |

* | |

* Use of this source code is governed by a BSD-style license | |

* that can be found in the LICENSE file in the root of the source | |

* tree. An additional intellectual property rights grant can be found | |

* in the file PATENTS. All contributing project authors may | |

* be found in the AUTHORS file in the root of the source tree. | |

*/ | |

/****************************************************************** | |

iLBC Speech Coder ANSI-C Source Code | |

WebRtcIlbcfix_Lsf2Lsp.c | |

******************************************************************/ | |

#include "defines.h" | |

#include "constants.h" | |

/*----------------------------------------------------------------* | |

* conversion from lsf to lsp coefficients | |

*---------------------------------------------------------------*/ | |

void WebRtcIlbcfix_Lsf2Lsp( | |

int16_t *lsf, /* (i) lsf in Q13 values between 0 and pi */ | |

int16_t *lsp, /* (o) lsp in Q15 values between -1 and 1 */ | |

int16_t m /* (i) number of coefficients */ | |

) { | |

int16_t i, k; | |

int16_t diff; /* difference, which is used for the | |

linear approximation (Q8) */ | |

int16_t freq; /* normalized frequency in Q15 (0..1) */ | |

int32_t tmpW32; | |

for(i=0; i<m; i++) | |

{ | |

freq = (int16_t)((lsf[i] * 20861) >> 15); | |

/* 20861: 1.0/(2.0*PI) in Q17 */ | |

/* | |

Upper 8 bits give the index k and | |

Lower 8 bits give the difference, which needs | |

to be approximated linearly | |

*/ | |

k = freq >> 8; | |

diff = (freq&0x00ff); | |

/* Guard against getting outside table */ | |

if (k>63) { | |

k = 63; | |

} | |

/* Calculate linear approximation */ | |

tmpW32 = WebRtcIlbcfix_kCosDerivative[k] * diff; | |

lsp[i] = WebRtcIlbcfix_kCos[k] + (int16_t)(tmpW32 >> 12); | |

} | |

return; | |

} |