Wed Aug 18 22:34:34 2010

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_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 171 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().

00172 {
00173    int i;
00174    
00175    /*
00176     *  Set up mu-law conversion table
00177     */
00178 #ifndef G711_NEW_ALGORITHM
00179    for (i = 0;i < 256;i++) {
00180       short mu,e,f,y;
00181       static short etab[]={0,132,396,924,1980,4092,8316,16764};
00182       
00183       mu = 255-i;
00184       e = (mu & 0x70)/16;
00185       f = mu & 0x0f;
00186       y = f * (1 << (e + 3));
00187       y += etab[e];
00188       if (mu & 0x80) y = -y;
00189       __ast_mulaw[i] = y;
00190    }
00191    /* set up the reverse (mu-law) conversion table */
00192    for (i = -32768; i < 32768; i++) {
00193       __ast_lin2mu[((unsigned short)i) >> 2] = linear2ulaw(i);
00194    }
00195 #else
00196    
00197    for (i = 0; i < 256; i++) {
00198       __ast_mulaw[i] = ulaw2linear(i);
00199    }
00200    /* set up the reverse (mu-law) conversion table */
00201    for (i = 0; i <= 32768; i += AST_ULAW_STEP) {
00202       AST_LIN2MU_LOOKUP(i) = linear2ulaw(i, 0 /* half-cooked */);
00203    }
00204 #endif
00205    
00206 #ifdef TEST_CODING_TABLES
00207    for (i = -32768; i < 32768; ++i) {
00208 #ifndef G711_NEW_ALGORITHM
00209       unsigned char e1 = linear2ulaw(i);
00210 #else
00211       unsigned char e1 = linear2ulaw(i, 1);
00212 #endif
00213       short d1 = ulaw2linear(e1);
00214       unsigned char e2 = AST_LIN2MU(i);
00215       short d2 = ulaw2linear(e2);
00216       short d3 = AST_MULAW(e1);
00217       
00218       if (e1 != e2 || d1 != d3 || d2 != d3) {
00219          ast_log(LOG_WARNING, "u-Law coding tables test failed on %d: e1=%u, e2=%u, d1=%d, d2=%d\n",
00220                i, (unsigned)e1, (unsigned)e2, (int)d1, (int)d2);
00221       }
00222    }
00223    ast_log(LOG_NOTICE, "u-Law coding table test complete.\n");
00224 #endif /* TEST_CODING_TABLES */
00225    
00226 #ifdef TEST_TANDEM_TRANSCODING
00227    /* tandem transcoding test */
00228    for (i = -32768; i < 32768; ++i) {
00229       unsigned char e1 = AST_LIN2MU(i);
00230       short d1 = AST_MULAW(e1);
00231       unsigned char e2 = AST_LIN2MU(d1);
00232       short d2 = AST_MULAW(e2);
00233       unsigned char e3 = AST_LIN2MU(d2);
00234       short d3 = AST_MULAW(e3);
00235       
00236       if (i < 0 && e1 == 0x7f && e2 == 0xff && e3 == 0xff)
00237          continue; /* known and normal negative 0 case */
00238       
00239       if (e1 != e2 || e2 != e3 || d1 != d2 || d2 != d3) {
00240          ast_log(LOG_WARNING, "u-Law tandem transcoding test failed on %d: e1=%u, e2=%u, d1=%d, d2=%d, d3=%d\n",
00241                i, (unsigned)e1, (unsigned)e2, (int)d1, (int)d2, (int)d3);
00242       }
00243    }
00244    ast_log(LOG_NOTICE, "u-Law tandem transcoding test complete.\n");
00245 #endif /* TEST_TANDEM_TRANSCODING */
00246 }


Variable Documentation

unsigned char __ast_lin2mu[16384]

converts signed linear to mulaw

Definition at line 47 of file ulaw.c.

short __ast_mulaw[256]

help

Definition at line 48 of file ulaw.c.


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