Fri Jul 24 00:42:01 2009

Asterisk developer's documentation


ulaw.h File Reference

u-Law to Signed linear conversion More...

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Defines

#define AST_LIN2MU(a)   (__ast_lin2mu[((unsigned short)(a)) >> 2])
#define AST_MULAW(a)   (__ast_mulaw[(a)])
#define AST_ULAW_BIT_LOSS   3
#define AST_ULAW_SIGN_BIT   0x80
#define AST_ULAW_STEP   (1 << AST_ULAW_BIT_LOSS)
#define AST_ULAW_TAB_SIZE   (32768 / AST_ULAW_STEP + 1)

Functions

void ast_ulaw_init (void)
 Set up mu-law conversion table.

Variables

unsigned char __ast_lin2mu [16384]
 converts signed linear to mulaw
short __ast_mulaw [256]


Detailed Description

u-Law to Signed linear conversion

Definition in file ulaw.h.


Define Documentation

#define AST_LIN2MU (  )     (__ast_lin2mu[((unsigned short)(a)) >> 2])

Definition at line 49 of file ulaw.h.

Referenced by ast_dsp_process(), ast_ulaw_init(), fill_rxgain(), fill_txgain(), lintoulaw(), lintoulaw_framein(), load_module(), and make_tone_burst().

#define AST_MULAW (  )     (__ast_mulaw[(a)])

Definition at line 85 of file ulaw.h.

Referenced by ast_dsp_process(), ast_ulaw_init(), calc_energy(), fill_rxgain(), fill_txgain(), load_module(), tdd_feed(), ulawtolin(), and ulawtolin_framein().

#define AST_ULAW_BIT_LOSS   3

Definition at line 32 of file ulaw.h.

#define AST_ULAW_SIGN_BIT   0x80

Definition at line 35 of file ulaw.h.

#define AST_ULAW_STEP   (1 << AST_ULAW_BIT_LOSS)

Definition at line 33 of file ulaw.h.

Referenced by ast_ulaw_init().

#define AST_ULAW_TAB_SIZE   (32768 / AST_ULAW_STEP + 1)

Definition at line 34 of file ulaw.h.


Function Documentation

void ast_ulaw_init ( void   ) 

Set up mu-law conversion table.

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

Definition at line 170 of file ulaw.c.

References AST_LIN2MU, ast_log(), AST_MULAW, AST_ULAW_STEP, f, linear2ulaw(), LOG_NOTICE, and LOG_WARNING.

Referenced by load_module(), and main().

00171 {
00172    int i;
00173    
00174    /*
00175     *  Set up mu-law conversion table
00176     */
00177 #ifndef G711_NEW_ALGORITHM
00178    for (i = 0;i < 256;i++) {
00179       short mu,e,f,y;
00180       static short etab[]={0,132,396,924,1980,4092,8316,16764};
00181       
00182       mu = 255-i;
00183       e = (mu & 0x70)/16;
00184       f = mu & 0x0f;
00185       y = f * (1 << (e + 3));
00186       y += etab[e];
00187       if (mu & 0x80) y = -y;
00188       __ast_mulaw[i] = y;
00189    }
00190    /* set up the reverse (mu-law) conversion table */
00191    for (i = -32768; i < 32768; i++) {
00192       __ast_lin2mu[((unsigned short)i) >> 2] = linear2ulaw(i);
00193    }
00194 #else
00195    
00196    for (i = 0; i < 256; i++) {
00197       __ast_mulaw[i] = ulaw2linear(i);
00198    }
00199    /* set up the reverse (mu-law) conversion table */
00200    for (i = 0; i <= 32768; i += AST_ULAW_STEP) {
00201       AST_LIN2MU_LOOKUP(i) = linear2ulaw(i, 0 /* half-cooked */);
00202    }
00203 #endif
00204    
00205 #ifdef TEST_CODING_TABLES
00206    for (i = -32768; i < 32768; ++i) {
00207 #ifndef G711_NEW_ALGORITHM
00208       unsigned char e1 = linear2ulaw(i);
00209 #else
00210       unsigned char e1 = linear2ulaw(i, 1);
00211 #endif
00212       short d1 = ulaw2linear(e1);
00213       unsigned char e2 = AST_LIN2MU(i);
00214       short d2 = ulaw2linear(e2);
00215       short d3 = AST_MULAW(e1);
00216       
00217       if (e1 != e2 || d1 != d3 || d2 != d3) {
00218          ast_log(LOG_WARNING, "u-Law coding tables test failed on %d: e1=%u, e2=%u, d1=%d, d2=%d\n",
00219                i, (unsigned)e1, (unsigned)e2, (int)d1, (int)d2);
00220       }
00221    }
00222    ast_log(LOG_NOTICE, "u-Law coding table test complete.\n");
00223 #endif /* TEST_CODING_TABLES */
00224    
00225 #ifdef TEST_TANDEM_TRANSCODING
00226    /* tandem transcoding test */
00227    for (i = -32768; i < 32768; ++i) {
00228       unsigned char e1 = AST_LIN2MU(i);
00229       short d1 = AST_MULAW(e1);
00230       unsigned char e2 = AST_LIN2MU(d1);
00231       short d2 = AST_MULAW(e2);
00232       unsigned char e3 = AST_LIN2MU(d2);
00233       short d3 = AST_MULAW(e3);
00234       
00235       if (i < 0 && e1 == 0x7f && e2 == 0xff && e3 == 0xff)
00236          continue; /* known and normal negative 0 case */
00237       
00238       if (e1 != e2 || e2 != e3 || d1 != d2 || d2 != d3) {
00239          ast_log(LOG_WARNING, "u-Law tandem transcoding test failed on %d: e1=%u, e2=%u, d1=%d, d2=%d, d3=%d\n",
00240                i, (unsigned)e1, (unsigned)e2, (int)d1, (int)d2, (int)d3);
00241       }
00242    }
00243    ast_log(LOG_NOTICE, "u-Law tandem transcoding test complete.\n");
00244 #endif /* TEST_TANDEM_TRANSCODING */
00245 }


Variable Documentation

unsigned char __ast_lin2mu[16384]

converts signed linear to mulaw

Definition at line 46 of file ulaw.c.

short __ast_mulaw[256]

help

Definition at line 47 of file ulaw.c.


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