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 ( a   )     (__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 ( a   )     (__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 154 of file alaw.c.

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

Referenced by main().

00155 {
00156    int i;
00157    /*
00158     *  Set up mu-law conversion table
00159     */
00160 #ifndef G711_NEW_ALGORITHM
00161    for (i = 0; i < 256; i++) {
00162       __ast_alaw[i] = alaw2linear(i);
00163    }
00164    /* set up the reverse (mu-law) conversion table */
00165    for (i = -32768; i < 32768; i++) {
00166       __ast_lin2a[((unsigned short)i) >> 3] = linear2alaw(i);
00167    }
00168 #else
00169    for (i = 0; i < 256; i++) {
00170       __ast_alaw[i] = alaw2linear(i);
00171    }
00172    /* set up the reverse (a-law) conversion table */
00173    for (i = 0; i <= 32768; i += AST_ALAW_STEP) {
00174       AST_LIN2A_LOOKUP(i) = linear2alaw(i, 0 /* half-cooked */);
00175    }
00176 #endif
00177 
00178 #ifdef TEST_CODING_TABLES
00179    for (i = -32768; i < 32768; ++i) {
00180 #ifndef G711_NEW_ALGORITHM
00181       unsigned char e1 = linear2alaw(i);
00182 #else
00183       unsigned char e1 = linear2alaw(i, 1);
00184 #endif
00185       short d1 = alaw2linear(e1);
00186       unsigned char e2 = AST_LIN2A(i);
00187       short d2 = alaw2linear(e2);
00188       short d3 = AST_ALAW(e1);
00189 
00190       if (e1 != e2 || d1 != d3 || d2 != d3) {
00191          ast_log(LOG_WARNING, "a-Law coding tables test failed on %d: e1=%u, e2=%u, d1=%d, d2=%d\n",
00192                i, (unsigned)e1, (unsigned)e2, (int)d1, (int)d2);
00193       }
00194    }
00195    ast_log(LOG_NOTICE, "a-Law coding tables test complete.\n");
00196 #endif /* TEST_CODING_TABLES */
00197 
00198 #ifdef TEST_TANDEM_TRANSCODING
00199    /* tandem transcoding test */
00200    for (i = -32768; i < 32768; ++i) {
00201       unsigned char e1 = AST_LIN2A(i);
00202       short d1 = AST_ALAW(e1);
00203       unsigned char e2 = AST_LIN2A(d1);
00204       short d2 = AST_ALAW(e2);
00205       unsigned char e3 = AST_LIN2A(d2);
00206       short d3 = AST_ALAW(e3);
00207 
00208       if (e1 != e2 || e2 != e3 || d1 != d2 || d2 != d3) {
00209          ast_log(LOG_WARNING, "a-Law tandem transcoding test failed on %d: e1=%u, e2=%u, d1=%d, d2=%d, d3=%d\n",
00210                i, (unsigned)e1, (unsigned)e2, (int)d1, (int)d2, (int)d3);
00211       }
00212    }
00213    ast_log(LOG_NOTICE, "a-Law tandem transcoding test complete.\n");
00214 #endif /* TEST_TANDEM_TRANSCODING */
00215 
00216 }


Variable Documentation

short __ast_alaw[256]

help

Definition at line 152 of file alaw.c.

unsigned char __ast_lin2a[8192]

converts signed linear to alaw

Definition at line 148 of file alaw.c.


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