112 lines
3.0 KiB
C
112 lines
3.0 KiB
C
/*
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* iLBC - a library for the iLBC codec
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*
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* gainquant.c - The iLBC low bit rate speech codec.
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*
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* Adapted by Steve Underwood <steveu@coppice.org> from the reference
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* iLBC code supplied in RFC3951.
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*
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* Original code Copyright (C) The Internet Society (2004).
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* All changes to produce this version Copyright (C) 2008 by Steve Underwood
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* All Rights Reserved.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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*
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* $Id: gainquant.c,v 1.2 2008/03/06 12:27:38 steveu Exp $
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*/
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/*! \file */
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#ifdef HAVE_CONFIG_H
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#include <config.h>
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#endif
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#include <inttypes.h>
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#include <math.h>
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#include <string.h>
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#include "constants.h"
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#include "filter.h"
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#include "gainquant.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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float gainquant( /* (o) quantized gain value */
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float in, /* (i) gain value */
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float maxIn, /* (i) maximum of gain value */
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int cblen, /* (i) number of quantization indices */
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int *index) /* (o) quantization index */
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{
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int i;
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int tindex;
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float minmeasure;
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float measure;
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const float *cb;
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float scale;
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/* ensure a lower bound on the scaling factor */
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scale = maxIn;
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if (scale < 0.1f)
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scale = 0.1f;
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/* select the quantization table */
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if (cblen == 8)
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cb = gain_sq3Tbl;
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else if (cblen == 16)
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cb = gain_sq4Tbl;
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else
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cb = gain_sq5Tbl;
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/* select the best index in the quantization table */
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minmeasure = 10000000.0f;
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tindex = 0;
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for (i = 0; i < cblen; i++)
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{
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measure = (in-scale*cb[i])*(in-scale*cb[i]);
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if (measure < minmeasure)
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{
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tindex = i;
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minmeasure = measure;
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}
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}
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*index = tindex;
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/* return the quantized value */
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return scale*cb[tindex];
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}
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/*----------------------------------------------------------------*
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* decoder for quantized gains in the gain-shape coding of
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* residual
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*---------------------------------------------------------------*/
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float gaindequant( /* (o) quantized gain value */
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int index, /* (i) quantization index */
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float maxIn, /* (i) maximum of unquantized gain */
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int cblen) /* (i) number of quantization indices */
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{
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float scale;
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/* obtain correct scale factor */
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scale = fabsf(maxIn);
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if (scale < 0.1f)
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scale = 0.1f;
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/* select the quantization table and return the decoded value */
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if (cblen == 8)
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return scale*gain_sq3Tbl[index];
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if (cblen == 16)
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return scale*gain_sq4Tbl[index];
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if (cblen == 32)
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return scale*gain_sq5Tbl[index];
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return 0.0;
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}
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