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f05740bc9b
git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@15543 d0543943-73ff-0310-b7d9-9358b9ac24b2
71 lines
2.0 KiB
C
71 lines
2.0 KiB
C
/*
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* broadvoice - a library for the BroadVoice 16 and 32 codecs
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*
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* lsp2a.c -
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*
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* Adapted by Steve Underwood <steveu@coppice.org> from code which is
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* Copyright 2000-2009 Broadcom Corporation
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*
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* All rights reserved.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License version 2.1,
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* as published by the Free Software Foundation.
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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. See the
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* GNU Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*
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* $Id: lsp2a.c,v 1.1.1.1 2009/11/19 12:10:48 steveu Exp $
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*/
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/*! \file */
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#if defined(HAVE_CONFIG_H)
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#include "config.h"
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#endif
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#include <math.h>
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#include "typedef.h"
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#include "bvcommon.h"
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#define OR (LPCO+1) /* Maximum LPC order */
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#define PI 3.14159265358979
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void lsp2a(
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Float *lsp, /* (i) LSP vector */
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Float *a) /* (o) LPC coefficients */
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{
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Float c1, c2, p[OR], q[OR];
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int orderd2, n, i, nor;
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orderd2=LPCO/2;
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for (i = 1; i <= LPCO ; i++)
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p[i] = q[i]= 0.;
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/* Get Q & P polyn. less the (1 +- z-1) ( or (1 +- z-2) ) factor */
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p[0] = q[0] = 1.;
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for (n = 1; n <= orderd2; n++)
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{
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nor= 2 * n;
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c1 = 2. * cos((double)PI*lsp[nor-1]);
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c2 = 2. * cos((double)PI*lsp[nor-2]);
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for (i = nor; i >= 2; i--)
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{
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q[i] += q[i-2] - c1*q[i-1];
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p[i] += p[i-2] - c2*p[i-1];
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}
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q[1] -= c1;
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p[1] -= c2;
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}
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/* Get the the predictor coeff. */
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a[0] = 1.;
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a[1] = 0.5 * (p[1] + q[1]);
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for (i=1, n=2; i < LPCO ; i++, n++)
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a[n] = 0.5 * (p[i] + p[n] + q[n] - q[i]);
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}
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