/*?libst.c?-?portable?sound?tools?library
*/

#include?“libst.h“

#ifndef?FAST_ULAW_CONVERSION

#undef?ZEROTRAP??????/*?turn?off?the?trap?as?per?the?MIL-STD?*/
#define?uBIAS?0x84???/*?define?the?add-in?bias?for?16?bit?samples?*/
#define?uCLIP?32635
#define?ACLIP?31744

unsigned?char
st_linear_to_ulaw（?sample?）
int?sample;
????{
????static?int?exp_lut[256]?=?{0011222233333333
???????????????????????????????4444444444444444
???????????????????????????????5555555555555555
???????????????????????????????5555555555555555
???????????????????????????????6666666666666666
???????????????????????????????6666666666666666
???????????????????????????????6666666666666666
???????????????????????????????6666666666666666
???????????????????????????????7777777777777777
???????????????????????????????7777777777777777
???????????????????????????????7777777777777777
???????????????????????????????7777777777777777
???????????????????????????????7777777777777777
???????????????????????????????7777777777777777
???????????????????????????????7777777777777777
???????????????????????????????7777777777777777};
????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?>?uCLIP?）?sample?=?uCLIP;		/*?clip?the?magnitude?*/

????/*?Convert?from?16?bit?linear?to?ulaw.?*/
????sample?=?sample?+?uBIAS;
????exponent?=?exp_lut[（?sample?>>?7?）?&?0xFF];
????mantissa?=?（?sample?>>?（?exponent?+?3?）?）?&?0x0F;
????ulawbyte?=?~?（?sign?|?（?exponent?<#ifdef?ZEROTRAP
????if?（?ulawbyte?==?0?）?ulawbyte?=?0x02;	/*?optional?CCITT?trap?*/
#endif

????return?ulawbyte;
????}

/*
**?This?routine?converts?from?ulaw?to?16?bit?linear.
**
**?Craig?Reese:?IDA/Supercomputing?Research?Center
**?29?September?1989
**
**?References:
**?1）?CCITT?Recommendation?G.711??（very?difficult?to?follow）
**?2）?MIL-STD-188-113“Interoperability?and?Performance?Standards
**?????for?Analog-to_Digital?Conversion?Techniques“
**?????17?February?1987
**
**?Input:?8?bit?ulaw?sample
**?Output:?signed?16?bit?linear?sample
*/

int
st_ulaw_to_linear（?ulawbyte?）
unsigned?char?ulawbyte;
????{
????static?int?exp_lut[8]?=?{?0?132?396?924?1980?4092?8316?16764?};
????int?sign?exponent?mantissa?sample;

????ulawbyte?=?~?ulawbyte;
????sign?=?（?ulawbyte?&?0x80?）;
????exponent?=?（?ulawbyte?>>?4?）?&?0x07;
????mantissa?=?ulawbyte?&?0x0F;
????sample?=?exp_lut[exponent]?+?（?mantissa?<????if?（?sign?!=?0?）?sample?=?-sample;

????return?sample;
????}

#else

unsigned?char?ulaw_comp_t

?屬性????????????大小?????日期????時間???名稱
-----------?---------??----------?-----??----

?????文件?????187472??2000-09-25?19:29??A律u律_實現\libst.c

?????文件???????1331??2000-09-25?19:29??A律u律_實現\libst.h

?????目錄??????????0??2020-11-10?20:45??A律u律_實現

-----------?---------??----------?-----??----

???????????????188803????????????????????3