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/* difftime( time_t, time_t )
This file is part of the Public Domain C Library (PDCLib).
Permission is granted to use, modify, and / or redistribute at will.
*/
#include <time.h>
#ifndef REGTEST
double difftime( time_t time1, time_t time0 )
{
/* If we want to avoid rounding errors and overflows, we need to be
careful with the exact type of time_t being unknown to us.
The code below is based on tzcode's difftime.c, which is in the
public domain, so clarified as of 1996-06-05 by Arthur David Olson.
*/
/* If double is large enough, simply covert and substract
(assuming that the larger type has more precision).
*/
if ( sizeof( time_t ) < sizeof( double ) )
{
return (double)time1 - (double)time0;
}
/* The difference of two unsigned values cannot overflow if the
minuend is greater or equal to the subtrahend.
*/
if ( ! _PDCLIB_TYPE_SIGNED( time_t ) )
{
return ( time1 >= time0 ) ? (double)( time1 - time0 ) : -(double)( time0 - time1 );
}
/* Use uintmax_t if wide enough. */
if ( sizeof( time_t ) <= sizeof( _PDCLIB_uintmax_t ) )
{
_PDCLIB_uintmax_t t1 = time1, t0 = time0;
return ( time1 >= time0 ) ? t1 - t0 : -(double)( t0 - t1 );
}
/* If both times have the same sign, their difference cannot overflow. */
if ( ( time1 < 0 ) == ( time0 < 0 ) )
{
return time1 - time0;
}
/* The times have opposite signs, and uintmax_t is too narrow.
This suffers from double rounding; attempt to lessen that
by using long double temporaries.
*/
{
long double t1 = time1, t0 = time0;
return t1 - t0;
}
}
#endif
#ifdef TEST
#include "_PDCLIB_test.h"
int main( void )
{
TESTCASE( NO_TESTDRIVER );
return TEST_RESULTS;
}
#endif
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