/*
** This file is in the public domain, so clarified as of
** 1996-06-05 by Arthur David Olson.
**
** $FreeBSD: head/contrib/tzcode/stdtime/difftime.c 192625 2009-05-23 06:31:50Z edwin $
*/
/*LINTLIBRARY*/

#include "namespace.h"
#include "private.h"    /* for time_t and TYPE_SIGNED */
#include "un-namespace.h"

double
difftime(time_t time1, time_t time0)
{
        /*
        ** If (sizeof (double) > sizeof (time_t)) simply convert and subtract
        ** (assuming that the larger type has more precision).
        */
        if (sizeof (double) > sizeof (time_t))
                return (double) time1 - (double) time0;
        if (!TYPE_SIGNED(time_t)) {
                /*
                ** The difference of two unsigned values can't overflow
                ** if the minuend is greater than or equal to the subtrahend.
                */
                if (time1 >= time0)
                        return            time1 - time0;
                else    return -(double) (time0 - time1);
        }
        /*
        ** Handle cases where both time1 and time0 have the same sign
        ** (meaning that their difference cannot overflow).
        */
        if ((time1 < 0) == (time0 < 0))
                return time1 - time0;
        /*
        ** time1 and time0 have opposite signs.
        ** Punt if uintmax_t is too narrow.
        ** This suffers from double rounding; attempt to lessen that
        ** by using long double temporaries.
        */
        if (sizeof (uintmax_t) < sizeof (time_t))
                return (long double) time1 - (long double) time0;
        /*
        ** Stay calm...decent optimizers will eliminate the complexity below.
        */
        if (time1 >= 0 /* && time0 < 0 */)
                return    (uintmax_t) time1 + (uintmax_t) (-1 - time0) + 1;
        return -(double) ((uintmax_t) time0 + (uintmax_t) (-1 - time1) + 1);
}