blob: 84278a434a82342d337f432aeb64a5fc81eb6931 [file] [log] [blame]
/*
* 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(
WebRtc_Word16 *lsf, /* (i) lsf in Q13 values between 0 and pi */
WebRtc_Word16 *lsp, /* (o) lsp in Q15 values between -1 and 1 */
WebRtc_Word16 m /* (i) number of coefficients */
) {
WebRtc_Word16 i, k;
WebRtc_Word16 diff; /* difference, which is used for the
linear approximation (Q8) */
WebRtc_Word16 freq; /* normalized frequency in Q15 (0..1) */
WebRtc_Word32 tmpW32;
for(i=0; i<m; i++)
{
freq = (WebRtc_Word16)WEBRTC_SPL_MUL_16_16_RSFT(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 = WEBRTC_SPL_RSHIFT_W16(freq, 8);
diff = (freq&0x00ff);
/* Guard against getting outside table */
if (k>63) {
k = 63;
}
/* Calculate linear approximation */
tmpW32 = WEBRTC_SPL_MUL_16_16(WebRtcIlbcfix_kCosDerivative[k], diff);
lsp[i] = WebRtcIlbcfix_kCos[k]+(WebRtc_Word16)(WEBRTC_SPL_RSHIFT_W32(tmpW32, 12));
}
return;
}