diff options
Diffstat (limited to 'ulaw.c')
-rwxr-xr-x | ulaw.c | 88 |
1 files changed, 88 insertions, 0 deletions
@@ -0,0 +1,88 @@ +/* + * Asterisk -- A telephony toolkit for Linux. + * + * u-Law to Signed linear conversion + * + * Copyright (C) 1999, Mark Spencer + * + * Mark Spencer <markster@linux-support.net> + * + * This program is free software, distributed under the terms of + * the GNU General Public License + */ + +#include <asterisk/ulaw.h> + +#define ZEROTRAP /* turn on the trap as per the MIL-STD */ +#define BIAS 0x84 /* define the add-in bias for 16 bit samples */ +#define CLIP 32635 + +unsigned char ast_lin2mu[65536]; +short ast_mulaw[256]; + +static unsigned char +linear2ulaw(short sample) +{ + 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); +} + +void ast_ulaw_init(void) +{ + int i; + /* + * Set up mu-law conversion table + */ + 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 = 0; i < 65536; i++) + { + ast_lin2mu[i] = linear2ulaw(i - 32768); + } + +} + |