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 | ( | a | ) | (__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 | ( | a | ) | (__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_STEP (1 << AST_ULAW_BIT_LOSS) |
Definition at line 33 of file ulaw.h.
Referenced by ast_ulaw_init().
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().
{
int i;
/*
* Set up mu-law conversion table
*/
#ifndef G711_NEW_ALGORITHM
for (i = 0;i < 256;i++) {
short mu,e,f,y;
static const short etab[]={0,132,396,924,1980,4092,8316,16764};
mu = 255-i;
e = (mu & 0x70)/16;
f = mu & 0x0f;
y = f * (1 << (e + 3));
y += etab[e];
if (mu & 0x80) y = -y;
__ast_mulaw[i] = y;
}
/* set up the reverse (mu-law) conversion table */
for (i = -32768; i < 32768; i++) {
__ast_lin2mu[((unsigned short)i) >> 2] = linear2ulaw(i);
}
#else
for (i = 0; i < 256; i++) {
__ast_mulaw[i] = ulaw2linear(i);
}
/* set up the reverse (mu-law) conversion table */
for (i = 0; i <= 32768; i += AST_ULAW_STEP) {
AST_LIN2MU_LOOKUP(i) = linear2ulaw(i, 0 /* half-cooked */);
}
#endif
#ifdef TEST_CODING_TABLES
for (i = -32768; i < 32768; ++i) {
#ifndef G711_NEW_ALGORITHM
unsigned char e1 = linear2ulaw(i);
#else
unsigned char e1 = linear2ulaw(i, 1);
#endif
short d1 = ulaw2linear(e1);
unsigned char e2 = AST_LIN2MU(i);
short d2 = ulaw2linear(e2);
short d3 = AST_MULAW(e1);
if (e1 != e2 || d1 != d3 || d2 != d3) {
ast_log(LOG_WARNING, "u-Law coding tables test failed on %d: e1=%u, e2=%u, d1=%d, d2=%d\n",
i, (unsigned)e1, (unsigned)e2, (int)d1, (int)d2);
}
}
ast_log(LOG_NOTICE, "u-Law coding table test complete.\n");
#endif /* TEST_CODING_TABLES */
#ifdef TEST_TANDEM_TRANSCODING
/* tandem transcoding test */
for (i = -32768; i < 32768; ++i) {
unsigned char e1 = AST_LIN2MU(i);
short d1 = AST_MULAW(e1);
unsigned char e2 = AST_LIN2MU(d1);
short d2 = AST_MULAW(e2);
unsigned char e3 = AST_LIN2MU(d2);
short d3 = AST_MULAW(e3);
if (i < 0 && e1 == 0x7f && e2 == 0xff && e3 == 0xff)
continue; /* known and normal negative 0 case */
if (e1 != e2 || e2 != e3 || d1 != d2 || d2 != d3) {
ast_log(LOG_WARNING, "u-Law tandem transcoding test failed on %d: e1=%u, e2=%u, d1=%d, d2=%d, d3=%d\n",
i, (unsigned)e1, (unsigned)e2, (int)d1, (int)d2, (int)d3);
}
}
ast_log(LOG_NOTICE, "u-Law tandem transcoding test complete.\n");
#endif /* TEST_TANDEM_TRANSCODING */
}
Variable Documentation
| unsigned char __ast_lin2mu[16384] |
| short __ast_mulaw[256] |
