alaw.c File Reference

a-Law to Signed linear conversion More...

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

Include dependency graph for alaw.c:

Go to the source code of this file.

Macros
#define	AMI_MASK   0x55

Functions
static short int	alaw2linear (unsigned char alaw)
void	ast_alaw_init (void)
	To init the alaw to slinear conversion stuff, this needs to be run. More...
static unsigned char	linear2alaw (short int linear)

Variables
short	__ast_alaw [256]
unsigned char	__ast_lin2a [8192]
	converts signed linear to alaw More...

Detailed Description

a-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 alaw.c.

Macro Definition Documentation

AMI_MASK

#define AMI_MASK   0x55

Definition at line 36 of file alaw.c.

Referenced by alaw2linear(), and linear2alaw().

Function Documentation

alaw2linear()

static short int alaw2linear ( unsigned char  alaw )

inlinestatic

Definition at line 112 of file alaw.c.

References AMI_MASK, and AST_ALAW_AMI_MASK.

Referenced by ast_alaw_init().

{
   int i;
   int seg;

   alaw ^= AMI_MASK;
   i = ((alaw & 0x0F) << 4) + 8 /* rounding error */;
   seg = (((int) alaw & 0x70) >> 4);
   if (seg) {
      i = (i + 0x100) << (seg - 1);
   }
   return (short int) ((alaw & 0x80) ? i : -i);
}

ast_alaw_init()

void ast_alaw_init

(

void

)

To init the alaw to slinear conversion stuff, this needs to be run.

Definition at line 152 of file alaw.c.

References __ast_alaw, __ast_lin2a, alaw2linear(), AST_ALAW, AST_ALAW_STEP, AST_LIN2A, ast_log, linear2alaw(), 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++) {
      __ast_alaw[i] = alaw2linear(i);
   }
   /* set up the reverse (mu-law) conversion table */
   for (i = -32768; i < 32768; i++) {
      __ast_lin2a[((unsigned short)i) >> 3] = linear2alaw(i);
   }
#else
   for (i = 0; i < 256; i++) {
      __ast_alaw[i] = alaw2linear(i);
   }
   /* set up the reverse (a-law) conversion table */
   for (i = 0; i <= 32768; i += AST_ALAW_STEP) {
      AST_LIN2A_LOOKUP(i) = linear2alaw(i, 0 /* half-cooked */);
   }
#endif

#ifdef TEST_CODING_TABLES
   for (i = -32768; i < 32768; ++i) {
#ifndef G711_NEW_ALGORITHM
      unsigned char e1 = linear2alaw(i);
#else
      unsigned char e1 = linear2alaw(i, 1);
#endif
      short d1 = alaw2linear(e1);
      unsigned char e2 = AST_LIN2A(i);
      short d2 = alaw2linear(e2);
      short d3 = AST_ALAW(e1);

      if (e1 != e2 || d1 != d3 || d2 != d3) {
         ast_log(LOG_WARNING, "a-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, "a-Law coding tables test complete.\n");
#endif /* TEST_CODING_TABLES */

#ifdef TEST_TANDEM_TRANSCODING
   /* tandem transcoding test */
   for (i = -32768; i < 32768; ++i) {
      unsigned char e1 = AST_LIN2A(i);
      short d1 = AST_ALAW(e1);
      unsigned char e2 = AST_LIN2A(d1);
      short d2 = AST_ALAW(e2);
      unsigned char e3 = AST_LIN2A(d2);
      short d3 = AST_ALAW(e3);

      if (e1 != e2 || e2 != e3 || d1 != d2 || d2 != d3) {
         ast_log(LOG_WARNING, "a-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, "a-Law tandem transcoding test complete.\n");
#endif /* TEST_TANDEM_TRANSCODING */

}

linear2alaw()

static unsigned char linear2alaw ( short int  linear )

inlinestatic

Definition at line 38 of file alaw.c.

References AMI_MASK, and AST_ALAW_AMI_MASK.

Referenced by ast_alaw_init().

{
   int mask;
   int seg;
   int pcm_val;
   static int seg_end[8] =
      {
         0xFF, 0x1FF, 0x3FF, 0x7FF, 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF
      };

   pcm_val = linear;
   if (pcm_val >= 0) {
      /* Sign (7th) bit = 1 */
      mask = AMI_MASK | 0x80;
   } else {
      /* Sign bit = 0 */
      mask = AMI_MASK;
      pcm_val = -pcm_val;
   }

   /* Convert the scaled magnitude to segment number. */
   for (seg = 0; seg < 8; seg++) {
      if (pcm_val <= seg_end[seg]) {
         break;
      }
   }
   /* Combine the sign, segment, and quantization bits. */
   return ((seg << 4) | ((pcm_val >> ((seg) ? (seg + 3) : 4)) & 0x0F)) ^ mask;
}

Variable Documentation

__ast_alaw

short __ast_alaw[256]

help

Definition at line 150 of file alaw.c.

Referenced by ast_alaw_init().

__ast_lin2a

unsigned char __ast_lin2a[8192]

converts signed linear to alaw

Definition at line 146 of file alaw.c.

Referenced by ast_alaw_init().