Sat Sep 16 05:47:48 2006

Asterisk developer's documentation


alaw.c File Reference

u-Law to Signed linear conversion More...

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

Go to the source code of this file.

Defines

#define AMI_MASK   0x55

Functions

static short int alaw2linear (unsigned char alaw)
void ast_alaw_init (void)
static unsigned char linear2alaw (short int linear)

Variables

short __ast_alaw [256]
unsigned char __ast_lin2a [8192]


Detailed Description

u-Law to Signed linear conversion

Definition in file alaw.c.


Define Documentation

#define AMI_MASK   0x55

Definition at line 31 of file alaw.c.

Referenced by alaw2linear(), and linear2alaw().


Function Documentation

static short int alaw2linear ( unsigned char  alaw  )  [inline, static]

Definition at line 67 of file alaw.c.

References AMI_MASK.

Referenced by ast_alaw_init().

00068 {
00069     int i;
00070     int seg;
00071 
00072     alaw ^= AMI_MASK;
00073     i = ((alaw & 0x0F) << 4);
00074     seg = (((int) alaw & 0x70) >> 4);
00075     if (seg)
00076         i = (i + 0x100) << (seg - 1);
00077     return (short int) ((alaw & 0x80)  ?  i  :  -i);
00078 }

void ast_alaw_init ( void   ) 

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

Definition at line 83 of file alaw.c.

References alaw2linear(), and linear2alaw().

Referenced by main().

00084 {
00085    int i;
00086    /* 
00087     *  Set up mu-law conversion table
00088     */
00089    for(i = 0;i < 256;i++)
00090       {
00091            __ast_alaw[i] = alaw2linear(i);
00092       }
00093      /* set up the reverse (mu-law) conversion table */
00094    for(i = -32768; i < 32768; i++)
00095       {
00096       __ast_lin2a[((unsigned short)i) >> 3] = linear2alaw(i);
00097       }
00098 
00099 }

static unsigned char linear2alaw ( short int  linear  )  [inline, static]

Definition at line 33 of file alaw.c.

References AMI_MASK.

Referenced by ast_alaw_init().

00034 {
00035     int mask;
00036     int seg;
00037     int pcm_val;
00038     static int seg_end[8] =
00039     {
00040          0xFF, 0x1FF, 0x3FF, 0x7FF, 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF
00041     };
00042     
00043     pcm_val = linear;
00044     if (pcm_val >= 0)
00045     {
00046         /* Sign (7th) bit = 1 */
00047         mask = AMI_MASK | 0x80;
00048     }
00049     else
00050     {
00051         /* Sign bit = 0 */
00052         mask = AMI_MASK;
00053         pcm_val = -pcm_val;
00054     }
00055 
00056     /* Convert the scaled magnitude to segment number. */
00057     for (seg = 0;  seg < 8;  seg++)
00058     {
00059         if (pcm_val <= seg_end[seg])
00060        break;
00061     }
00062     /* Combine the sign, segment, and quantization bits. */
00063     return  ((seg << 4) | ((pcm_val >> ((seg)  ?  (seg + 3)  :  4)) & 0x0F)) ^ mask;
00064 }


Variable Documentation

short __ast_alaw[256]

help

Definition at line 81 of file alaw.c.

unsigned char __ast_lin2a[8192]

Definition at line 80 of file alaw.c.


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