101 lines
2.2 KiB
C
101 lines
2.2 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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*/
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#include "asterisk.h"
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ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
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#include "asterisk/alaw.h"
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#define AMI_MASK 0x55
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static inline unsigned char linear2alaw (short int linear)
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{
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int mask;
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int seg;
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int pcm_val;
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static int seg_end[8] =
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{
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0xFF, 0x1FF, 0x3FF, 0x7FF, 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF
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};
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pcm_val = linear;
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if (pcm_val >= 0)
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{
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/* Sign (7th) bit = 1 */
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mask = AMI_MASK | 0x80;
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}
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else
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{
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/* Sign bit = 0 */
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mask = AMI_MASK;
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pcm_val = -pcm_val;
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}
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/* Convert the scaled magnitude to segment number. */
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for (seg = 0; seg < 8; seg++)
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{
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if (pcm_val <= seg_end[seg])
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break;
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}
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/* Combine the sign, segment, and quantization bits. */
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return ((seg << 4) | ((pcm_val >> ((seg) ? (seg + 3) : 4)) & 0x0F)) ^ mask;
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}
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/*- End of function --------------------------------------------------------*/
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static inline short int alaw2linear (unsigned char alaw)
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{
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int i;
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int seg;
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alaw ^= AMI_MASK;
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i = ((alaw & 0x0F) << 4);
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seg = (((int) alaw & 0x70) >> 4);
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if (seg)
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i = (i + 0x100) << (seg - 1);
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return (short int) ((alaw & 0x80) ? i : -i);
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}
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unsigned char __ast_lin2a[8192];
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short __ast_alaw[256];
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void ast_alaw_init(void)
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{
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int i;
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/*
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* Set up mu-law conversion table
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*/
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for(i = 0;i < 256;i++)
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{
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__ast_alaw[i] = alaw2linear(i);
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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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{
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__ast_lin2a[((unsigned short)i) >> 3] = linear2alaw(i);
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}
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}
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