alaw.c File Reference

a-Law to Signed linear conversion More...

#include "asterisk.h"
#include "asterisk/alaw.h"
#include "asterisk/logger.h"

Include dependency graph for alaw.c:

Go to the source code of this file.

Macros
#define	AMI_MASK   0x55

Functions
static short int	alaw2linear (unsigned char alaw)
void	ast_alaw_init (void)
	To init the alaw to slinear conversion stuff, this needs to be run.
static unsigned char	linear2alaw (short int linear)

Variables
short	__ast_alaw [256]
unsigned char	__ast_lin2a [8192]
	converts signed linear to alaw

Detailed Description

a-Law to Signed linear conversion

Author

Mark Spencer marks.nosp@m.ter@.nosp@m.digiu.nosp@m.m.co.nosp@m.m

Definition in file alaw.c.

Macro Definition Documentation

AMI_MASK

#define AMI_MASK   0x55

Definition at line 36 of file alaw.c.

Function Documentation

alaw2linear()

static short int alaw2linear ( unsigned char  alaw )

inlinestatic

Definition at line 112 of file alaw.c.

{
    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);
}

References alaw, and AMI_MASK.

Referenced by ast_alaw_init().

ast_alaw_init()

void ast_alaw_init

(

void

)

To init the alaw to slinear conversion stuff, this needs to be run.

Definition at line 152 of file alaw.c.

{
    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 */
 
}

References __ast_alaw, __ast_lin2a, alaw2linear(), AST_ALAW, AST_ALAW_STEP, AST_LIN2A, ast_log, linear2alaw(), LOG_NOTICE, and LOG_WARNING.

Referenced by asterisk_daemon().

linear2alaw()

static unsigned char linear2alaw ( short int  linear )

inlinestatic

Definition at line 38 of file alaw.c.

{
    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;
}

References AMI_MASK.

Referenced by ast_alaw_init().

Variable Documentation

__ast_alaw

short __ast_alaw[256]

help

Definition at line 150 of file alaw.c.

Referenced by ast_alaw_init().

__ast_lin2a

unsigned char __ast_lin2a[8192]

converts signed linear to alaw

Definition at line 146 of file alaw.c.

Referenced by ast_alaw_init().