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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_XcorrCoef.c
******************************************************************/
#include "defines.h"
/*----------------------------------------------------------------*
* cross correlation which finds the optimal lag for the
* crossCorr*crossCorr/(energy) criteria
*---------------------------------------------------------------*/
int WebRtcIlbcfix_XcorrCoef(
int16_t *target, /* (i) first array */
int16_t *regressor, /* (i) second array */
int16_t subl, /* (i) dimension arrays */
int16_t searchLen, /* (i) the search lenght */
int16_t offset, /* (i) samples offset between arrays */
int16_t step /* (i) +1 or -1 */
){
int k;
int16_t maxlag;
int16_t pos;
int16_t max;
int16_t crossCorrScale, Energyscale;
int16_t crossCorrSqMod, crossCorrSqMod_Max;
int32_t crossCorr, Energy;
int16_t crossCorrmod, EnergyMod, EnergyMod_Max;
int16_t *tp, *rp;
int16_t *rp_beg, *rp_end;
int16_t totscale, totscale_max;
int16_t scalediff;
int32_t newCrit, maxCrit;
int shifts;
/* Initializations, to make sure that the first one is selected */
crossCorrSqMod_Max=0;
EnergyMod_Max=WEBRTC_SPL_WORD16_MAX;
totscale_max=-500;
maxlag=0;
pos=0;
/* Find scale value and start position */
if (step==1) {
max=WebRtcSpl_MaxAbsValueW16(regressor, (int16_t)(subl+searchLen-1));
rp_beg = regressor;
rp_end = ®ressor[subl];
} else { /* step==-1 */
max=WebRtcSpl_MaxAbsValueW16(®ressor[-searchLen], (int16_t)(subl+searchLen-1));
rp_beg = ®ressor[-1];
rp_end = ®ressor[subl-1];
}
/* Introduce a scale factor on the Energy in int32_t in
order to make sure that the calculation does not
overflow */
if (max>5000) {
shifts=2;
} else {
shifts=0;
}
/* Calculate the first energy, then do a +/- to get the other energies */
Energy=WebRtcSpl_DotProductWithScale(regressor, regressor, subl, shifts);
for (k=0;k<searchLen;k++) {
tp = target;
rp = ®ressor[pos];
crossCorr=WebRtcSpl_DotProductWithScale(tp, rp, subl, shifts);
if ((Energy>0)&&(crossCorr>0)) {
/* Put cross correlation and energy on 16 bit word */
crossCorrScale=(int16_t)WebRtcSpl_NormW32(crossCorr)-16;
crossCorrmod=(int16_t)WEBRTC_SPL_SHIFT_W32(crossCorr, crossCorrScale);
Energyscale=(int16_t)WebRtcSpl_NormW32(Energy)-16;
EnergyMod=(int16_t)WEBRTC_SPL_SHIFT_W32(Energy, Energyscale);
/* Square cross correlation and store upper int16_t */
crossCorrSqMod=(int16_t)WEBRTC_SPL_MUL_16_16_RSFT(crossCorrmod, crossCorrmod, 16);
/* Calculate the total number of (dynamic) right shifts that have
been performed on (crossCorr*crossCorr)/energy
*/
totscale=Energyscale-(crossCorrScale<<1);
/* Calculate the shift difference in order to be able to compare the two
(crossCorr*crossCorr)/energy in the same domain
*/
scalediff=totscale-totscale_max;
scalediff=WEBRTC_SPL_MIN(scalediff,31);
scalediff=WEBRTC_SPL_MAX(scalediff,-31);
/* Compute the cross multiplication between the old best criteria
and the new one to be able to compare them without using a
division */
if (scalediff<0) {
newCrit = ((int32_t)crossCorrSqMod*EnergyMod_Max)>>(-scalediff);
maxCrit = ((int32_t)crossCorrSqMod_Max*EnergyMod);
} else {
newCrit = ((int32_t)crossCorrSqMod*EnergyMod_Max);
maxCrit = ((int32_t)crossCorrSqMod_Max*EnergyMod)>>scalediff;
}
/* Store the new lag value if the new criteria is larger
than previous largest criteria */
if (newCrit > maxCrit) {
crossCorrSqMod_Max = crossCorrSqMod;
EnergyMod_Max = EnergyMod;
totscale_max = totscale;
maxlag = k;
}
}
pos+=step;
/* Do a +/- to get the next energy */
Energy += step*(WEBRTC_SPL_RSHIFT_W32(
((int32_t)(*rp_end)*(*rp_end)) - ((int32_t)(*rp_beg)*(*rp_beg)),
shifts));
rp_beg+=step;
rp_end+=step;
}
return(maxlag+offset);
}
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