alaw.h

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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 */