Thu Oct 11 06:47:27 2012

Asterisk developer's documentation


alaw.h File Reference

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

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Defines

#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.


Define Documentation

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

#define AST_ALAW_AMI_MASK   0x55

Definition at line 36 of file alaw.h.

#define AST_ALAW_BIT_LOSS   4

Definition at line 32 of file alaw.h.

#define AST_ALAW_SIGN_BIT   0x80

Definition at line 35 of file alaw.h.

#define AST_ALAW_STEP   (1 << AST_ALAW_BIT_LOSS)

Definition at line 33 of file alaw.h.

Referenced by ast_alaw_init().

#define AST_ALAW_TAB_SIZE   (32768 / AST_ALAW_STEP + 1)

Definition at line 34 of file alaw.h.

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


Function Documentation

void ast_alaw_init ( void   ) 

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

Definition at line 150 of file alaw.c.

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

Referenced by main().

00151 {
00152    int i;
00153    /*
00154     *  Set up mu-law conversion table
00155     */
00156 #ifndef G711_NEW_ALGORITHM
00157    for (i = 0; i < 256; i++) {
00158       __ast_alaw[i] = alaw2linear(i);
00159    }
00160    /* set up the reverse (mu-law) conversion table */
00161    for (i = -32768; i < 32768; i++) {
00162       __ast_lin2a[((unsigned short)i) >> 3] = linear2alaw(i);
00163    }
00164 #else
00165    for (i = 0; i < 256; i++) {
00166       __ast_alaw[i] = alaw2linear(i);
00167    }
00168    /* set up the reverse (a-law) conversion table */
00169    for (i = 0; i <= 32768; i += AST_ALAW_STEP) {
00170       AST_LIN2A_LOOKUP(i) = linear2alaw(i, 0 /* half-cooked */);
00171    }
00172 #endif
00173 
00174 #ifdef TEST_CODING_TABLES
00175    for (i = -32768; i < 32768; ++i) {
00176 #ifndef G711_NEW_ALGORITHM
00177       unsigned char e1 = linear2alaw(i);
00178 #else
00179       unsigned char e1 = linear2alaw(i, 1);
00180 #endif
00181       short d1 = alaw2linear(e1);
00182       unsigned char e2 = AST_LIN2A(i);
00183       short d2 = alaw2linear(e2);
00184       short d3 = AST_ALAW(e1);
00185 
00186       if (e1 != e2 || d1 != d3 || d2 != d3) {
00187          ast_log(LOG_WARNING, "a-Law coding tables test failed on %d: e1=%u, e2=%u, d1=%d, d2=%d\n",
00188                i, (unsigned)e1, (unsigned)e2, (int)d1, (int)d2);
00189       }
00190    }
00191    ast_log(LOG_NOTICE, "a-Law coding tables test complete.\n");
00192 #endif /* TEST_CODING_TABLES */
00193 
00194 #ifdef TEST_TANDEM_TRANSCODING
00195    /* tandem transcoding test */
00196    for (i = -32768; i < 32768; ++i) {
00197       unsigned char e1 = AST_LIN2A(i);
00198       short d1 = AST_ALAW(e1);
00199       unsigned char e2 = AST_LIN2A(d1);
00200       short d2 = AST_ALAW(e2);
00201       unsigned char e3 = AST_LIN2A(d2);
00202       short d3 = AST_ALAW(e3);
00203 
00204       if (e1 != e2 || e2 != e3 || d1 != d2 || d2 != d3) {
00205          ast_log(LOG_WARNING, "a-Law tandem transcoding test failed on %d: e1=%u, e2=%u, d1=%d, d2=%d, d3=%d\n",
00206                i, (unsigned)e1, (unsigned)e2, (int)d1, (int)d2, (int)d3);
00207       }
00208    }
00209    ast_log(LOG_NOTICE, "a-Law tandem transcoding test complete.\n");
00210 #endif /* TEST_TANDEM_TRANSCODING */
00211 
00212 }


Variable Documentation

short __ast_alaw[256]

help

Definition at line 148 of file alaw.c.

unsigned char __ast_lin2a[8192]

converts signed linear to alaw

Definition at line 144 of file alaw.c.


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