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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_GainQuant.c
******************************************************************/
#include "defines.h"
#include "constants.h"
/*----------------------------------------------------------------*
* quantizer for the gain in the gain-shape coding of residual
*---------------------------------------------------------------*/
int16_t WebRtcIlbcfix_GainQuant( /* (o) quantized gain value */
int16_t gain, /* (i) gain value Q14 */
int16_t maxIn, /* (i) maximum of gain value Q14 */
int16_t stage, /* (i) The stage of the search */
int16_t *index /* (o) quantization index */
) {
int16_t scale, returnVal, cblen;
int32_t gainW32, measure1, measure2;
const int16_t *cbPtr, *cb;
int loc, noMoves, noChecks, i;
/* ensure a lower bound (0.1) on the scaling factor */
scale = WEBRTC_SPL_MAX(1638, maxIn);
/* select the quantization table and calculate
the length of the table and the number of
steps in the binary search that are needed */
cb = WebRtcIlbcfix_kGain[stage];
cblen = 32>>stage;
noChecks = 4-stage;
/* Multiply the gain with 2^14 to make the comparison
easier and with higher precision */
gainW32 = WEBRTC_SPL_LSHIFT_W32((int32_t)gain, 14);
/* Do a binary search, starting in the middle of the CB
loc - defines the current position in the table
noMoves - defines the number of steps to move in the CB in order
to get next CB location
*/
loc = cblen>>1;
noMoves = loc;
cbPtr = cb + loc; /* Centre of CB */
for (i=noChecks;i>0;i--) {
noMoves>>=1;
measure1=WEBRTC_SPL_MUL_16_16(scale, (*cbPtr));
/* Move up if gain is larger, otherwise move down in table */
measure1 = measure1 - gainW32;
if (0>measure1) {
cbPtr+=noMoves;
loc+=noMoves;
} else {
cbPtr-=noMoves;
loc-=noMoves;
}
}
/* Check which value is the closest one: loc-1, loc or loc+1 */
measure1=WEBRTC_SPL_MUL_16_16(scale, (*cbPtr));
if (gainW32>measure1) {
/* Check against value above loc */
measure2=WEBRTC_SPL_MUL_16_16(scale, (*(cbPtr+1)));
if ((measure2-gainW32)<(gainW32-measure1)) {
loc+=1;
}
} else {
/* Check against value below loc */
measure2=WEBRTC_SPL_MUL_16_16(scale, (*(cbPtr-1)));
if ((gainW32-measure2)<=(measure1-gainW32)) {
loc-=1;
}
}
/* Guard against getting outside the table. The calculation above can give a location
which is one above the maximum value (in very rare cases) */
loc=WEBRTC_SPL_MIN(loc, (cblen-1));
*index=loc;
/* Calculate the quantized gain value (in Q14) */
returnVal=(int16_t)((WEBRTC_SPL_MUL_16_16(scale, cb[loc])+8192)>>14);
/* return the quantized value */
return(returnVal);
}
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