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/*
* 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 "modules/audio_coding/codecs/ilbc/lsf_to_lsp.h"
#include "modules/audio_coding/codecs/ilbc/constants.h"
#include "modules/audio_coding/codecs/ilbc/defines.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;
}
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