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