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difftime.c revision 1.18.2.1 
      1     /*	$NetBSD: difftime.c,v 1.18.2.1 2018/10/20 06:58:22 pgoyette Exp $	*/
      2     
      3     /* Return the difference between two timestamps.  */
      4     
      5     /*
      6     ** This file is in the public domain, so clarified as of
      7     ** 1996-06-05 by Arthur David Olson.
      8     */
      9     
     10     #include <sys/cdefs.h>
     11     #if defined(LIBC_SCCS) && !defined(lint)
     12     #if 0
     13     static char	elsieid[] = "@(#)difftime.c	8.1";
     14     #else
     15     __RCSID("$NetBSD: difftime.c,v 1.18.2.1 2018/10/20 06:58:22 pgoyette Exp $");
     16     #endif
     17     #endif /* LIBC_SCCS and not lint */
     18     
     19     /*LINTLIBRARY*/
     20     
     21     #include "private.h"	/* for time_t and TYPE_SIGNED */
     22     
     23     /* Return -X as a double.  Using this avoids casting to 'double'.  */
     24     static double
     25     dminus(double x)
     26     {
     27     	return -x;
     28     }
     29     
     30     double
     31     difftime(time_t time1, time_t time0)
     32     {
     33     	/*
     34     	** If double is large enough, simply convert and subtract
     35     	** (assuming that the larger type has more precision).
     36     	*/
     37     	/*CONSTCOND*/
     38     	if (sizeof (time_t) < sizeof (double)) {
     39     		double t1 = time1, t0 = time0;
     40     		return t1 - t0;
     41      	}
     42     
     43     	/*
     44     	** The difference of two unsigned values can't overflow
     45     	** if the minuend is greater than or equal to the subtrahend.
     46     	*/
     47     	if (!TYPE_SIGNED(time_t))
     48     		return time0 <= time1 ? time1 - time0 : dminus(time0 - time1);
     49     
     50     	/* Use uintmax_t if wide enough.  */
     51     	/*CONSTCOND*/
     52     	if (sizeof (time_t) <= sizeof (uintmax_t)) {
     53     		uintmax_t t1 = time1, t0 = time0;
     54     		return time0 <= time1 ? t1 - t0 : dminus(t0 - t1);
     55     	}
     56     
     57     	/*
     58     	** Handle cases where both time1 and time0 have the same sign
     59     	** (meaning that their difference cannot overflow).
     60     	*/
     61     	if ((time1 < 0) == (time0 < 0))
     62     		return time1 - time0;
     63     
     64     	/*
     65     	** The values have opposite signs and uintmax_t is too narrow.
     66     	** This suffers from double rounding; attempt to lessen that
     67     	** by using long double temporaries.
     68     	*/
     69     	{
     70     		long double t1 = time1, t0 = time0;
     71     		return t1 - t0;
     72     	}
     73     }
     74