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bb547203bf
In order to eliminate the WebRTC Subtree mirror in Chromium, WebRTC is moving the content of the src/webrtc directory up to the src/ directory. NOPRESUBMIT=true NOTREECHECKS=true NOTRY=true TBR=tommi@webrtc.org Bug: chromium:611808 Change-Id: Iac59c5b51b950f174119565bac87955a7994bc38 Reviewed-on: https://webrtc-review.googlesource.com/1560 Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org> Reviewed-by: Henrik Kjellander <kjellander@webrtc.org> Cr-Commit-Position: refs/heads/master@{#19845}
84 lines
2.4 KiB
C
84 lines
2.4 KiB
C
/*
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* Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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/******************************************************************
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iLBC Speech Coder ANSI-C Source Code
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WebRtcIlbcfix_Lsp2Lsf.c
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******************************************************************/
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#include "defines.h"
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#include "constants.h"
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/*----------------------------------------------------------------*
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* conversion from LSP coefficients to LSF coefficients
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*---------------------------------------------------------------*/
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void WebRtcIlbcfix_Lsp2Lsf(
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int16_t *lsp, /* (i) lsp vector -1...+1 in Q15 */
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int16_t *lsf, /* (o) Lsf vector 0...Pi in Q13
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(ordered, so that lsf[i]<lsf[i+1]) */
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int16_t m /* (i) Number of coefficients */
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)
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{
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int16_t i, k;
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int16_t diff; /* diff between table value and desired value (Q15) */
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int16_t freq; /* lsf/(2*pi) (Q16) */
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int16_t *lspPtr, *lsfPtr, *cosTblPtr;
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int16_t tmp;
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/* set the index to maximum index value in WebRtcIlbcfix_kCos */
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k = 63;
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/*
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Start with the highest LSP and then work the way down
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For each LSP the lsf is calculated by first order approximation
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of the acos(x) function
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*/
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lspPtr = &lsp[9];
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lsfPtr = &lsf[9];
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cosTblPtr=(int16_t*)&WebRtcIlbcfix_kCos[k];
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for(i=m-1; i>=0; i--)
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{
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/*
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locate value in the table, which is just above lsp[i],
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basically an approximation to acos(x)
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*/
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while( (((int32_t)(*cosTblPtr)-(*lspPtr)) < 0)&&(k>0) )
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{
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k-=1;
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cosTblPtr--;
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}
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/* Calculate diff, which is used in the linear approximation of acos(x) */
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diff = (*lspPtr)-(*cosTblPtr);
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/*
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The linear approximation of acos(lsp[i]) :
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acos(lsp[i])= k*512 + (WebRtcIlbcfix_kAcosDerivative[ind]*offset >> 11)
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*/
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/* tmp (linear offset) in Q16 */
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tmp = (int16_t)((WebRtcIlbcfix_kAcosDerivative[k] * diff) >> 11);
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/* freq in Q16 */
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freq = (k << 9) + tmp;
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/* lsf = freq*2*pi */
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(*lsfPtr) = (int16_t)(((int32_t)freq*25736)>>15);
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lsfPtr--;
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lspPtr--;
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}
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return;
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}
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