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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_Lsf2Poly.c
******************************************************************/
#include "defines.h"
#include "lsf_to_lsp.h"
#include "get_lsp_poly.h"
#include "constants.h"
void WebRtcIlbcfix_Lsf2Poly(
int16_t *a, /* (o) predictor coefficients (order = 10) in Q12 */
int16_t *lsf /* (i) line spectral frequencies in Q13 */
) {
int32_t f[2][6]; /* f[0][] and f[1][] corresponds to
F1(z) and F2(z) respectivly */
int32_t *f1ptr, *f2ptr;
int16_t *a1ptr, *a2ptr;
int32_t tmpW32;
int16_t lsp[10];
int i;
/* Convert lsf to lsp */
WebRtcIlbcfix_Lsf2Lsp(lsf, lsp, LPC_FILTERORDER);
/* Get F1(z) and F2(z) from the lsp */
f1ptr=f[0];
f2ptr=f[1];
WebRtcIlbcfix_GetLspPoly(&lsp[0],f1ptr);
WebRtcIlbcfix_GetLspPoly(&lsp[1],f2ptr);
/* for i = 5 down to 1
Compute f1[i] += f1[i-1];
and f2[i] += f2[i-1];
*/
f1ptr=&f[0][5];
f2ptr=&f[1][5];
for (i=5; i>0; i--)
{
(*f1ptr) += (*(f1ptr-1));
(*f2ptr) -= (*(f2ptr-1));
f1ptr--;
f2ptr--;
}
/* Get the A(z) coefficients
a[0] = 1.0
for i = 1 to 5
a[i] = (f1[i] + f2[i] + round)>>13;
for i = 1 to 5
a[11-i] = (f1[i] - f2[i] + round)>>13;
*/
a[0]=4096;
a1ptr=&a[1];
a2ptr=&a[10];
f1ptr=&f[0][1];
f2ptr=&f[1][1];
for (i=5; i>0; i--)
{
tmpW32 = (*f1ptr) + (*f2ptr);
(*a1ptr) = (int16_t)WEBRTC_SPL_RSHIFT_W32((tmpW32+4096),13);
tmpW32 = (*f1ptr) - (*f2ptr);
(*a2ptr) = (int16_t)WEBRTC_SPL_RSHIFT_W32((tmpW32+4096),13);
a1ptr++;
a2ptr--;
f1ptr++;
f2ptr++;
}
return;
}
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