Wed Aug 7 17:16:14 2019

Asterisk developer's documentation


ulaw.h File Reference

u-Law to Signed linear conversion More...

Go to the source code of this file.

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])
#define AST_MULAW (  )     (__ast_mulaw[(a)])
#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 175 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().

00176 {
00177    int i;
00178    
00179    /*
00180     *  Set up mu-law conversion table
00181     */
00182 #ifndef G711_NEW_ALGORITHM
00183    for (i = 0;i < 256;i++) {
00184       short mu,e,f,y;
00185       static const short etab[]={0,132,396,924,1980,4092,8316,16764};
00186       
00187       mu = 255-i;
00188       e = (mu & 0x70)/16;
00189       f = mu & 0x0f;
00190       y = f * (1 << (e + 3));
00191       y += etab[e];
00192       if (mu & 0x80) y = -y;
00193       __ast_mulaw[i] = y;
00194    }
00195    /* set up the reverse (mu-law) conversion table */
00196    for (i = -32768; i < 32768; i++) {
00197       __ast_lin2mu[((unsigned short)i) >> 2] = linear2ulaw(i);
00198    }
00199 #else
00200    
00201    for (i = 0; i < 256; i++) {
00202       __ast_mulaw[i] = ulaw2linear(i);
00203    }
00204    /* set up the reverse (mu-law) conversion table */
00205    for (i = 0; i <= 32768; i += AST_ULAW_STEP) {
00206       AST_LIN2MU_LOOKUP(i) = linear2ulaw(i, 0 /* half-cooked */);
00207    }
00208 #endif
00209    
00210 #ifdef TEST_CODING_TABLES
00211    for (i = -32768; i < 32768; ++i) {
00212 #ifndef G711_NEW_ALGORITHM
00213       unsigned char e1 = linear2ulaw(i);
00214 #else
00215       unsigned char e1 = linear2ulaw(i, 1);
00216 #endif
00217       short d1 = ulaw2linear(e1);
00218       unsigned char e2 = AST_LIN2MU(i);
00219       short d2 = ulaw2linear(e2);
00220       short d3 = AST_MULAW(e1);
00221       
00222       if (e1 != e2 || d1 != d3 || d2 != d3) {
00223          ast_log(LOG_WARNING, "u-Law coding tables test failed on %d: e1=%u, e2=%u, d1=%d, d2=%d\n",
00224                i, (unsigned)e1, (unsigned)e2, (int)d1, (int)d2);
00225       }
00226    }
00227    ast_log(LOG_NOTICE, "u-Law coding table test complete.\n");
00228 #endif /* TEST_CODING_TABLES */
00229    
00230 #ifdef TEST_TANDEM_TRANSCODING
00231    /* tandem transcoding test */
00232    for (i = -32768; i < 32768; ++i) {
00233       unsigned char e1 = AST_LIN2MU(i);
00234       short d1 = AST_MULAW(e1);
00235       unsigned char e2 = AST_LIN2MU(d1);
00236       short d2 = AST_MULAW(e2);
00237       unsigned char e3 = AST_LIN2MU(d2);
00238       short d3 = AST_MULAW(e3);
00239       
00240       if (i < 0 && e1 == 0x7f && e2 == 0xff && e3 == 0xff)
00241          continue; /* known and normal negative 0 case */
00242       
00243       if (e1 != e2 || e2 != e3 || d1 != d2 || d2 != d3) {
00244          ast_log(LOG_WARNING, "u-Law tandem transcoding test failed on %d: e1=%u, e2=%u, d1=%d, d2=%d, d3=%d\n",
00245                i, (unsigned)e1, (unsigned)e2, (int)d1, (int)d2, (int)d3);
00246       }
00247    }
00248    ast_log(LOG_NOTICE, "u-Law tandem transcoding test complete.\n");
00249 #endif /* TEST_TANDEM_TRANSCODING */
00250 }


Variable Documentation

unsigned char __ast_lin2mu[16384]

converts signed linear to mulaw

Definition at line 51 of file ulaw.c.

short __ast_mulaw[256]

help

Definition at line 52 of file ulaw.c.


Generated on 7 Aug 2019 for Asterisk - The Open Source Telephony Project by  doxygen 1.6.1