A-Law to Signed linear conversion. More...

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Macros
#define	AST_ALAW(a) (__ast_alaw[(int)(a)])

#define	AST_ALAW_AMI_MASK 0x55

#define	AST_ALAW_BIT_LOSS 4

#define	AST_ALAW_SIGN_BIT 0x80

#define	AST_ALAW_STEP (1 << AST_ALAW_BIT_LOSS)

#define	AST_ALAW_TAB_SIZE (32768 / AST_ALAW_STEP + 1)

#define	AST_LIN2A(a) (__ast_lin2a[((unsigned short)(a)) >> 3])

Functions
void	ast_alaw_init (void)
	To init the alaw to slinear conversion stuff, this needs to be run.

Variables
short	__ast_alaw [256]

unsigned char	__ast_lin2a [8192]
	converts signed linear to alaw

Detailed Description

A-Law to Signed linear conversion.

Definition in file alaw.h.

Macro Definition Documentation

◆ AST_ALAW

#define AST_ALAW ( a ) (__ast_alaw[(int)(a)])

Definition at line 84 of file alaw.h.

◆ AST_ALAW_AMI_MASK

#define AST_ALAW_AMI_MASK 0x55

Definition at line 36 of file alaw.h.

◆ AST_ALAW_BIT_LOSS

#define AST_ALAW_BIT_LOSS 4

Definition at line 32 of file alaw.h.

◆ AST_ALAW_SIGN_BIT

#define AST_ALAW_SIGN_BIT 0x80

Definition at line 35 of file alaw.h.

◆ AST_ALAW_STEP

#define AST_ALAW_STEP (1 << AST_ALAW_BIT_LOSS)

Definition at line 33 of file alaw.h.

◆ AST_ALAW_TAB_SIZE

#define AST_ALAW_TAB_SIZE (32768 / AST_ALAW_STEP + 1)

Definition at line 34 of file alaw.h.

◆ AST_LIN2A

#define AST_LIN2A ( a ) (__ast_lin2a[((unsigned short)(a)) >> 3])

Definition at line 50 of file alaw.h.

Function Documentation

◆ 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().

Variable Documentation

◆ __ast_alaw

short __ast_alaw[256]

extern

help

Definition at line 150 of file alaw.c.

Referenced by ast_alaw_init().

◆ __ast_lin2a

unsigned char __ast_lin2a[8192]