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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_GetLspPoly.c
******************************************************************/
#include "modules/audio_coding/codecs/ilbc/get_lsp_poly.h"
#include "modules/audio_coding/codecs/ilbc/defines.h"
/*----------------------------------------------------------------*
* Construct the polynomials F1(z) and F2(z) from the LSP
* (Computations are done in Q24)
*
* The expansion is performed using the following recursion:
*
* f[0] = 1;
* tmp = -2.0 * lsp[0];
* f[1] = tmp;
* for (i=2; i<=5; i++) {
* b = -2.0 * lsp[2*i-2];
* f[i] = tmp*f[i-1] + 2.0*f[i-2];
* for (j=i; j>=2; j--) {
* f[j] = f[j] + tmp*f[j-1] + f[j-2];
* }
* f[i] = f[i] + tmp;
* }
*---------------------------------------------------------------*/
void WebRtcIlbcfix_GetLspPoly(
int16_t *lsp, /* (i) LSP in Q15 */
int32_t *f) /* (o) polonymial in Q24 */
{
int32_t tmpW32;
int i, j;
int16_t high, low;
int16_t *lspPtr;
int32_t *fPtr;
lspPtr = lsp;
fPtr = f;
/* f[0] = 1.0 (Q24) */
(*fPtr) = (int32_t)16777216;
fPtr++;
(*fPtr) = WEBRTC_SPL_MUL((*lspPtr), -1024);
fPtr++;
lspPtr+=2;
for(i=2; i<=5; i++)
{
(*fPtr) = fPtr[-2];
for(j=i; j>1; j--)
{
/* Compute f[j] = f[j] + tmp*f[j-1] + f[j-2]; */
high = (int16_t)(fPtr[-1] >> 16);
low = (int16_t)((fPtr[-1] & 0xffff) >> 1);
tmpW32 = 4 * high * *lspPtr + 4 * ((low * *lspPtr) >> 15);
(*fPtr) += fPtr[-2];
(*fPtr) -= tmpW32;
fPtr--;
}
*fPtr -= *lspPtr * (1 << 10);
fPtr+=i;
lspPtr+=2;
}
return;
}
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