alaw.c

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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
 *
 * \author Mark Spencer <markster@digium.com>
 */
 
/*** MODULEINFO
    <support_level>core</support_level>
 ***/
 
#include "asterisk.h"
 
#include "asterisk/alaw.h"
#include "asterisk/logger.h"
 
#ifndef G711_NEW_ALGORITHM
#define AMI_MASK 0x55
 
static inline unsigned char linear2alaw(short int linear)
{
    int mask;
    int seg;
    int pcm_val;
    static int seg_end[8] =
        {
            0xFF, 0x1FF, 0x3FF, 0x7FF, 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF
        };
 
    pcm_val = linear;
    if (pcm_val >= 0) {
        /* Sign (7th) bit = 1 */
        mask = AMI_MASK | 0x80;
    } else {
        /* Sign bit = 0 */
        mask = AMI_MASK;
        pcm_val = -pcm_val;
    }
 
    /* Convert the scaled magnitude to segment number. */
    for (seg = 0; seg < 8; seg++) {
        if (pcm_val <= seg_end[seg]) {
            break;
        }
    }
    /* Combine the sign, segment, and quantization bits. */
    return ((seg << 4) | ((pcm_val >> ((seg) ? (seg + 3) : 4)) & 0x0F)) ^ mask;
}
#else
static unsigned char linear2alaw(short sample, int full_coding)
{
    static const unsigned exp_lut[128] = {
        1,1,2,2,3,3,3,3,
        4,4,4,4,4,4,4,4,
        5,5,5,5,5,5,5,5,
        5,5,5,5,5,5,5,5,
        6,6,6,6,6,6,6,6,
        6,6,6,6,6,6,6,6,
        6,6,6,6,6,6,6,6,
        6,6,6,6,6,6,6,6,
        7,7,7,7,7,7,7,7,
        7,7,7,7,7,7,7,7,
        7,7,7,7,7,7,7,7,
        7,7,7,7,7,7,7,7,
        7,7,7,7,7,7,7,7,
        7,7,7,7,7,7,7,7,
        7,7,7,7,7,7,7,7,
        7,7,7,7,7,7,7,7 };
    unsigned sign, exponent, mantissa, mag;
    unsigned char alawbyte;
 
    ast_alaw_get_sign_mag(sample, &sign, &mag);
    if (mag > 32767)
        mag = 32767;        /* clip the magnitude for -32768 */
 
    exponent = exp_lut[(mag >> 8) & 0x7f];
    mantissa = (mag >> (exponent + 3)) & 0x0f;
    if (mag < 0x100)
        exponent = 0;
 
    if (full_coding) {
        /* full encoding, with sign and xform */
        alawbyte = (unsigned char)(sign | (exponent << 4) | mantissa);
        alawbyte ^= AST_ALAW_AMI_MASK;
    } else {
        /* half-cooked coding -- mantissa+exponent only (for lookup tab) */
        alawbyte = (exponent << 4) | mantissa;
    }
    return alawbyte;
}
#endif
 
#ifndef G711_NEW_ALGORITHM
static inline short int alaw2linear (unsigned char alaw)
{
    int i;
    int seg;
 
    alaw ^= AMI_MASK;
    i = ((alaw & 0x0F) << 4) + 8 /* rounding error */;
    seg = (((int) alaw & 0x70) >> 4);
    if (seg) {
        i = (i + 0x100) << (seg - 1);
    }
    return (short int) ((alaw & 0x80) ? i : -i);
}
#else
static inline short alaw2linear(unsigned char alawbyte)
{
    unsigned exponent, mantissa;
    short sample;
 
    alawbyte ^= AST_ALAW_AMI_MASK;
    exponent = (alawbyte & 0x70) >> 4;
    mantissa = alawbyte & 0x0f;
    sample = (mantissa << 4) + 8 /* rounding error */;
    if (exponent)
        sample = (sample + 0x100) << (exponent - 1);
    if (!(alawbyte & 0x80))
        sample = -sample;
    return sample;
}
#endif
 
 
 
#ifndef G711_NEW_ALGORITHM
unsigned char __ast_lin2a[8192];
#else
unsigned char __ast_lin2a[AST_ALAW_TAB_SIZE];
#endif
short __ast_alaw[256];
 
void ast_alaw_init(void)
{
    int i;
    /*
     *  Set up mu-law conversion table
     */
#ifndef G711_NEW_ALGORITHM
    for (i = 0; i < 256; i++) {
        __ast_alaw[i] = alaw2linear(i);
    }
    /* set up the reverse (mu-law) conversion table */
    for (i = -32768; i < 32768; i++) {
        __ast_lin2a[((unsigned short)i) >> 3] = linear2alaw(i);
    }
#else
    for (i = 0; i < 256; i++) {
        __ast_alaw[i] = alaw2linear(i);
    }
    /* set up the reverse (a-law) conversion table */
    for (i = 0; i <= 32768; i += AST_ALAW_STEP) {
        AST_LIN2A_LOOKUP(i) = linear2alaw(i, 0 /* half-cooked */);
    }
#endif
 
#ifdef TEST_CODING_TABLES
    for (i = -32768; i < 32768; ++i) {
#ifndef G711_NEW_ALGORITHM
        unsigned char e1 = linear2alaw(i);
#else
        unsigned char e1 = linear2alaw(i, 1);
#endif
        short d1 = alaw2linear(e1);
        unsigned char e2 = AST_LIN2A(i);
        short d2 = alaw2linear(e2);
        short d3 = AST_ALAW(e1);
 
        if (e1 != e2 || d1 != d3 || d2 != d3) {
            ast_log(LOG_WARNING, "a-Law coding tables test failed on %d: e1=%u, e2=%u, d1=%d, d2=%d\n",
                    i, (unsigned)e1, (unsigned)e2, (int)d1, (int)d2);
        }
    }
    ast_log(LOG_NOTICE, "a-Law coding tables test complete.\n");
#endif /* TEST_CODING_TABLES */
 
#ifdef TEST_TANDEM_TRANSCODING
    /* tandem transcoding test */
    for (i = -32768; i < 32768; ++i) {
        unsigned char e1 = AST_LIN2A(i);
        short d1 = AST_ALAW(e1);
        unsigned char e2 = AST_LIN2A(d1);
        short d2 = AST_ALAW(e2);
        unsigned char e3 = AST_LIN2A(d2);
        short d3 = AST_ALAW(e3);
 
        if (e1 != e2 || e2 != e3 || d1 != d2 || d2 != d3) {
            ast_log(LOG_WARNING, "a-Law tandem transcoding test failed on %d: e1=%u, e2=%u, d1=%d, d2=%d, d3=%d\n",
                    i, (unsigned)e1, (unsigned)e2, (int)d1, (int)d2, (int)d3);
        }
    }
    ast_log(LOG_NOTICE, "a-Law tandem transcoding test complete.\n");
#endif /* TEST_TANDEM_TRANSCODING */
 
}