ulaw.h File Reference

u-Law to Signed linear conversion More...

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Defines
#define	AST_LIN2MU_LOOKUP(mag)   __ast_lin2mu[((mag) + AST_ULAW_STEP / 2) >> AST_ULAW_BIT_LOSS]
#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
static unsigned char	AST_LIN2MU (short sample)
static void	ast_ulaw_get_sign_mag (short sample, unsigned *sign, unsigned *mag)
	convert signed linear sample to sign-magnitude pair for u-Law
void	ast_ulaw_init (void)
	Set up mu-law conversion table.
Variables
unsigned char	__ast_lin2mu [AST_ULAW_TAB_SIZE]
	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_LOOKUP

(

mag

)

__ast_lin2mu[((mag) + AST_ULAW_STEP / 2) >> AST_ULAW_BIT_LOSS]

Definition at line 53 of file ulaw.h.

Referenced by AST_LIN2MU(), and ast_ulaw_init().

#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_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.

Referenced by ast_ulaw_get_sign_mag().

#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

static unsigned char AST_LIN2MU

(

short

sample

)

[inline, static]

Definition at line 77 of file ulaw.h.

References AST_LIN2MU_LOOKUP, and ast_ulaw_get_sign_mag().

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

{
       unsigned mag, sign;
       ast_ulaw_get_sign_mag(sample, &sign, &mag);
       return ~(sign | AST_LIN2MU_LOOKUP(mag));
}

static void ast_ulaw_get_sign_mag	(	short	sample,
		unsigned *	sign,
		unsigned *	mag
	)			[inline, static]

convert signed linear sample to sign-magnitude pair for u-Law

Definition at line 58 of file ulaw.h.

References AST_ULAW_SIGN_BIT.

Referenced by AST_LIN2MU(), and linear2ulaw().

{
       /* It may look illogical to retrive the sign this way in both cases,
        * but this helps gcc eliminate the branch below and produces
        * faster code */
       *sign = ((unsigned short)sample >> 8) & AST_ULAW_SIGN_BIT;
#if defined(G711_REDUCED_BRANCHING)
       {
               unsigned dual_mag = (-sample << 16) | (unsigned short)sample;
               *mag = (dual_mag >> (*sign >> 3)) & 0xffffU;
       }
#else
       if (sample < 0)
               *mag = -sample;
       else
               *mag = sample;
#endif /* G711_REDUCED_BRANCHING */
}

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_LIN2MU_LOOKUP, ast_log(), AST_MULAW, AST_ULAW_STEP, f, linear2ulaw(), LOG_NOTICE, LOG_WARNING, and ulaw2linear().

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[AST_ULAW_TAB_SIZE]

converts signed linear to mulaw

Definition at line 99 of file ulaw.c.

short __ast_mulaw[256]

help

Definition at line 100 of file ulaw.c.