107 lines
2.7 KiB
C
107 lines
2.7 KiB
C
/*
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* Asterisk -- An open source telephony toolkit.
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*
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* Copyright (C) 1999 - 2005, Digium, Inc.
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*
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* Mark Spencer <markster@digium.com>
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*
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* See http://www.asterisk.org for more information about
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* the Asterisk project. Please do not directly contact
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* any of the maintainers of this project for assistance;
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* the project provides a web site, mailing lists and IRC
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* channels for your use.
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*
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* This program is free software, distributed under the terms of
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* the GNU General Public License Version 2. See the LICENSE file
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* at the top of the source tree.
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*/
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/*! \file
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*
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* \brief u-Law to Signed linear conversion
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*
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* \author Mark Spencer <markster@digium.com>
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*/
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#include "asterisk.h"
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ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
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#include "asterisk/ulaw.h"
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#define ZEROTRAP /*!< turn on the trap as per the MIL-STD */
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#define BIAS 0x84 /*!< define the add-in bias for 16 bit samples */
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#define CLIP 32635
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unsigned char __ast_lin2mu[16384];
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short __ast_mulaw[256];
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static unsigned char linear2ulaw(short sample)
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{
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static int exp_lut[256] = {
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0,0,1,1,2,2,2,2,3,3,3,3,3,3,3,3,
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4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
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5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
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5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
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6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
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6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
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6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
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6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
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7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
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7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
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7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
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7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
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7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
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7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
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7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
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7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7 };
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int sign, exponent, mantissa;
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unsigned char ulawbyte;
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/* Get the sample into sign-magnitude. */
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sign = (sample >> 8) & 0x80; /* set aside the sign */
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if (sign != 0)
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sample = -sample; /* get magnitude */
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if (sample > CLIP)
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sample = CLIP; /* clip the magnitude */
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/* Convert from 16 bit linear to ulaw. */
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sample = sample + BIAS;
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exponent = exp_lut[(sample >> 7) & 0xFF];
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mantissa = (sample >> (exponent + 3)) & 0x0F;
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ulawbyte = ~(sign | (exponent << 4) | mantissa);
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#ifdef ZEROTRAP
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if (ulawbyte == 0)
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ulawbyte = 0x02; /* optional CCITT trap */
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#endif
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return ulawbyte;
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}
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/*!
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* \brief Set up mu-law conversion table
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*/
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void ast_ulaw_init(void)
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{
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int i;
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for(i = 0;i < 256;i++) {
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short mu,e,f,y;
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static short etab[]={0,132,396,924,1980,4092,8316,16764};
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mu = 255-i;
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e = (mu & 0x70)/16;
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f = mu & 0x0f;
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y = f * (1 << (e + 3));
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y += etab[e];
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if (mu & 0x80) y = -y;
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__ast_mulaw[i] = y;
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}
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/* set up the reverse (mu-law) conversion table */
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for(i = -32768; i < 32768; i++) {
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__ast_lin2mu[((unsigned short)i) >> 2] = linear2ulaw(i);
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}
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}
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