Fri Jun 19 12:09:55 2009

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)])

Definition at line 84 of file alaw.h.

Referenced by alawtolin_framein(), ast_alaw_init(), ast_dsp_process(), calc_energy(), fill_rxgain(), fill_txgain(), and load_module().

#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])

Definition at line 50 of file alaw.h.

Referenced by ast_alaw_init(), ast_dsp_process(), fill_rxgain(), fill_txgain(), lintoalaw_framein(), and load_module().


Function Documentation

void ast_alaw_init ( void   ) 

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

Definition at line 149 of file alaw.c.

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

Referenced by main().

00150 {
00151    int i;
00152    /* 
00153     *  Set up mu-law conversion table
00154     */ 
00155 #ifndef G711_NEW_ALGORITHM
00156    for (i = 0; i < 256; i++) {
00157       __ast_alaw[i] = alaw2linear(i);
00158    }
00159    /* set up the reverse (mu-law) conversion table */
00160    for (i = -32768; i < 32768; i++) {
00161       __ast_lin2a[((unsigned short)i) >> 3] = linear2alaw(i);
00162    }
00163 #else
00164    for (i = 0; i < 256; i++) {
00165       __ast_alaw[i] = alaw2linear(i);
00166    }
00167    /* set up the reverse (a-law) conversion table */
00168    for (i = 0; i <= 32768; i += AST_ALAW_STEP) {
00169       AST_LIN2A_LOOKUP(i) = linear2alaw(i, 0 /* half-cooked */);
00170    }
00171 #endif
00172    
00173 #ifdef TEST_CODING_TABLES
00174    for (i = -32768; i < 32768; ++i) {
00175 #ifndef G711_NEW_ALGORITHM
00176       unsigned char e1 = linear2alaw(i);
00177 #else
00178       unsigned char e1 = linear2alaw(i, 1);
00179 #endif
00180       short d1 = alaw2linear(e1);
00181       unsigned char e2 = AST_LIN2A(i);
00182       short d2 = alaw2linear(e2);
00183       short d3 = AST_ALAW(e1);
00184       
00185       if (e1 != e2 || d1 != d3 || d2 != d3) {
00186          ast_log(LOG_WARNING, "a-Law coding tables test failed on %d: e1=%u, e2=%u, d1=%d, d2=%d\n",
00187                i, (unsigned)e1, (unsigned)e2, (int)d1, (int)d2);
00188       }
00189    }
00190    ast_log(LOG_NOTICE, "a-Law coding tables test complete.\n");
00191 #endif /* TEST_CODING_TABLES */
00192    
00193 #ifdef TEST_TANDEM_TRANSCODING
00194    /* tandem transcoding test */
00195    for (i = -32768; i < 32768; ++i) {
00196       unsigned char e1 = AST_LIN2A(i);
00197       short d1 = AST_ALAW(e1);
00198       unsigned char e2 = AST_LIN2A(d1);
00199       short d2 = AST_ALAW(e2);
00200       unsigned char e3 = AST_LIN2A(d2);
00201       short d3 = AST_ALAW(e3);
00202       
00203       if (e1 != e2 || e2 != e3 || d1 != d2 || d2 != d3) {
00204          ast_log(LOG_WARNING, "a-Law tandem transcoding test failed on %d: e1=%u, e2=%u, d1=%d, d2=%d, d3=%d\n",
00205                i, (unsigned)e1, (unsigned)e2, (int)d1, (int)d2, (int)d3);
00206       }
00207    }
00208    ast_log(LOG_NOTICE, "a-Law tandem transcoding test complete.\n");
00209 #endif /* TEST_TANDEM_TRANSCODING */
00210    
00211 }


Variable Documentation

short __ast_alaw[256]

help

Definition at line 147 of file alaw.c.

unsigned char __ast_lin2a[8192]

converts signed linear to alaw

Definition at line 143 of file alaw.c.


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