a-Law to Signed linear conversion More...
#include "asterisk.h"
#include "asterisk/alaw.h"
#include "asterisk/logger.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) |
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 |
a-Law to Signed linear conversion
Definition in file alaw.c.
#define AMI_MASK 0x55 |
Definition at line 34 of file alaw.c.
Referenced by alaw2linear(), and linear2alaw().
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; }
short __ast_alaw[256] |
unsigned char __ast_lin2a[8192] |