u-Law to Signed linear conversion More...

#include "asterisk.h"
#include "asterisk/ulaw.h"
#include "asterisk/logger.h"

Include dependency graph for ulaw.c:

Macros
#define	BIAS 0x84

#define	CLIP 32635

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

static unsigned char	linear2ulaw (short sample)

Variables
unsigned char	__ast_lin2mu [16384]
	converts signed linear to mulaw More...

short	__ast_mulaw [256]

Detailed Description

u-Law to Signed linear conversion

Author: Mark Spencer marks.nosp@m.ter@.nosp@m.digiu.nosp@m.m.co.nosp@m.m

Definition in file ulaw.c.

Macro Definition Documentation

◆ BIAS

#define BIAS 0x84

define the add-in bias for 16 bit samples

Definition at line 44 of file ulaw.c.

Referenced by linear2ulaw().

◆ CLIP

#define CLIP 32635

Definition at line 45 of file ulaw.c.

Referenced by linear2ulaw().

Function Documentation

◆ ast_ulaw_init()

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 173 of file ulaw.c.

References __ast_lin2mu, __ast_mulaw, AST_LIN2MU, ast_log, AST_MULAW, AST_ULAW_STEP, ast_udptl::f, linear2ulaw(), LOG_NOTICE, and LOG_WARNING.

Referenced by asterisk_daemon().

 {
  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 */
 }

◆ linear2ulaw()

static unsigned char linear2ulaw ( short sample )

static

Definition at line 52 of file ulaw.c.

References __ast_lin2mu, __ast_mulaw, AST_ULAW_TAB_SIZE, BIAS, and CLIP.

Referenced by ast_ulaw_init().

 {
  static int exp_lut[256] = {
  0,0,1,1,2,2,2,2,3,3,3,3,3,3,3,3,
  4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
  5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
  5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
  6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
  6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
  6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
  6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7 };
  int sign, exponent, mantissa;
  unsigned char ulawbyte;
 
  /* Get the sample into sign-magnitude. */
  sign = (sample >> 8) & 0x80; /* set aside the sign */
  if (sign != 0)
  sample = -sample; /* get magnitude */
  if (sample > CLIP)
  sample = CLIP; /* clip the magnitude */
 
  /* Convert from 16 bit linear to ulaw. */
  sample = sample + BIAS;
  exponent = exp_lut[(sample >> 7) & 0xFF];
  mantissa = (sample >> (exponent + 3)) & 0x0F;
  ulawbyte = ~(sign | (exponent << 4) | mantissa);
 
 #ifdef ZEROTRAP
  if (ulawbyte == 0)
  ulawbyte = 0x02; /* optional CCITT trap */
 #endif
 
  return ulawbyte;
 }

Variable Documentation

◆ __ast_lin2mu

unsigned char __ast_lin2mu[16384]

converts signed linear to mulaw

Definition at line 49 of file ulaw.c.

Referenced by ast_ulaw_init(), and linear2ulaw().

◆ __ast_mulaw

short __ast_mulaw[256]

help

Definition at line 50 of file ulaw.c.