u-Law to Signed linear conversion More...
#include "asterisk.h"
#include "asterisk/ulaw.h"
#include "asterisk/logger.h"
Go to the source code of this file.
Defines | |
#define | BIAS 0x84 |
#define | CLIP 32635 |
Functions | |
void | ast_ulaw_init (void) |
Set up mu-law conversion table. | |
static unsigned char | linear2ulaw (short sample) |
Variables | |
unsigned char | __ast_lin2mu [16384] |
converts signed linear to mulaw | |
short | __ast_mulaw [256] |
u-Law to Signed linear conversion
Definition in file ulaw.c.
#define BIAS 0x84 |
define the add-in bias for 16 bit samples
Definition at line 42 of file ulaw.c.
Referenced by linear2ulaw().
#define CLIP 32635 |
Definition at line 43 of file ulaw.c.
Referenced by linear2ulaw().
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 171 of file ulaw.c.
References AST_LIN2MU, ast_log(), AST_MULAW, AST_ULAW_STEP, f, linear2ulaw(), LOG_NOTICE, and LOG_WARNING.
Referenced by load_module(), and main().
{ int i; /* * Set up mu-law conversion table */ #ifndef G711_NEW_ALGORITHM for (i = 0;i < 256;i++) { short mu,e,f,y; static 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 */ }
static unsigned char linear2ulaw | ( | short | sample | ) | [static] |
Definition at line 50 of file ulaw.c.
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; }
unsigned char __ast_lin2mu[16384] |
short __ast_mulaw[256] |