a-Law to Signed linear conversion More...
Include dependency graph for alaw.c:
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) |
| To init the alaw to slinear conversion stuff, this needs to be run. | |
| static unsigned char | linear2alaw (short int linear) |
Variables | |
| short | __ast_alaw [256] |
| unsigned char | __ast_lin2a [8192] |
| converts signed linear to alaw | |
Detailed Description
a-Law to Signed linear conversion
Definition in file alaw.c.
Define Documentation
| #define AMI_MASK 0x55 |
Definition at line 34 of file alaw.c.
Referenced by alaw2linear(), and linear2alaw().
Function Documentation
| static short int alaw2linear | ( | unsigned char | alaw | ) | [inline, static] |
Definition at line 110 of file alaw.c.
References 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);
}
| void ast_alaw_init | ( | void | ) |
To init the alaw to slinear conversion stuff, this needs to be run.
Definition at line 150 of file alaw.c.
References alaw2linear(), AST_ALAW, AST_ALAW_STEP, AST_LIN2A, ast_log(), linear2alaw(), LOG_NOTICE, and LOG_WARNING.
Referenced by main().
{
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 */
}
| static unsigned char linear2alaw | ( | short int | linear | ) | [inline, static] |
Definition at line 36 of file alaw.c.
References 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
| short __ast_alaw[256] |
| unsigned char __ast_lin2a[8192] |
