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/*
* Asterisk -- An open source telephony toolkit.
*
* Copyright (C) 1999 - 2005, Digium, Inc.
*
* Mark Spencer <markster@digium.com>
*
* See http://www.asterisk.org for more information about
* the Asterisk project. Please do not directly contact
* any of the maintainers of this project for assistance;
* the project provides a web site, mailing lists and IRC
* channels for your use.
*
* This program is free software, distributed under the terms of
* the GNU General Public License Version 2. See the LICENSE file
* at the top of the source tree.
*/
/*! \file
* \brief A-Law to Signed linear conversion
*/
#ifndef _ASTERISK_ALAW_H
#define _ASTERISK_ALAW_H
/*! \brief
* To init the alaw to slinear conversion stuff, this needs to be run.
*/
void ast_alaw_init(void);
#define AST_ALAW_BIT_LOSS 4
#define AST_ALAW_STEP (1 << AST_ALAW_BIT_LOSS)
#define AST_ALAW_TAB_SIZE (32768 / AST_ALAW_STEP + 1)
#define AST_ALAW_SIGN_BIT 0x80
#define AST_ALAW_AMI_MASK 0x55
/*! \brief converts signed linear to alaw */
#ifndef G711_NEW_ALGORITHM
extern unsigned char __ast_lin2a[8192];
#else
extern unsigned char __ast_lin2a[AST_ALAW_TAB_SIZE];
#endif
/*! help */
extern short __ast_alaw[256];
#ifndef G711_NEW_ALGORITHM
#define AST_LIN2A(a) (__ast_lin2a[((unsigned short)(a)) >> 3])
#else
#define AST_LIN2A_LOOKUP(mag) \
__ast_lin2a[(mag) >> AST_ALAW_BIT_LOSS]
/*! \brief Convert signed linear sample to sign-magnitude pair for a-Law */
static inline void ast_alaw_get_sign_mag(short sample, unsigned *sign, unsigned *mag)
{
/* It may look illogical to retrive the sign this way in both cases,
* but this helps gcc eliminate the branch below and produces
* faster code */
*sign = ((unsigned short)sample >> 8) & AST_ALAW_SIGN_BIT;
#if defined(G711_REDUCED_BRANCHING)
{
unsigned dual_mag = (-sample << 16) | (unsigned short)sample;
*mag = (dual_mag >> (*sign >> 3)) & 0xffffU;
}
#else
if (sample < 0)
*mag = -sample;
else
*mag = sample;
#endif /* G711_REDUCED_BRANCHING */
*sign ^= AST_ALAW_SIGN_BIT;
}
static inline unsigned char AST_LIN2A(short sample)
{
unsigned mag, sign;
ast_alaw_get_sign_mag(sample, &sign, &mag);
return (sign | AST_LIN2A_LOOKUP(mag)) ^ AST_ALAW_AMI_MASK;
}
#endif
#define AST_ALAW(a) (__ast_alaw[(int)(a)])
#endif /* _ASTERISK_ALAW_H */
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