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difftime.c revision 1.11.2.1 
      1     /*	$NetBSD: difftime.c,v 1.11.2.1 2012/11/20 03:00:43 tls Exp $	*/
      2     
      3     /*
      4     ** This file is in the public domain, so clarified as of
      5     ** 1996-06-05 by Arthur David Olson.
      6     */
      7     
      8     #include <sys/cdefs.h>
      9     #if defined(LIBC_SCCS) && !defined(lint)
     10     #if 0
     11     static char	elsieid[] = "@(#)difftime.c	8.1";
     12     #else
     13     __RCSID("$NetBSD: difftime.c,v 1.11.2.1 2012/11/20 03:00:43 tls Exp $");
     14     #endif
     15     #endif /* LIBC_SCCS and not lint */
     16     
     17     /*LINTLIBRARY*/
     18     
     19     #include "private.h"	/* for time_t, TYPE_INTEGRAL, and TYPE_SIGNED */
     20     
     21     double
     22     difftime(const time_t time1, const time_t time0)
     23     {
     24     	/*
     25     	** If (sizeof (double) > sizeof (time_t)) simply convert and subtract
     26     	** (assuming that the larger type has more precision).
     27     	** This is the common real-world case circa 2004.
     28     	*/
     29     	/*CONSTCOND*/
     30     	if (sizeof (double) > sizeof (time_t))
     31     		return (double) time1 - (double) time0;
     32     	/*LINTED const not */
     33     	if (!TYPE_INTEGRAL(time_t)) {
     34     		/*
     35     		** time_t is floating.
     36     		*/
     37     		return time1 - time0;
     38     	}
     39     	/*LINTED const not */
     40     	if (!TYPE_SIGNED(time_t)) {
     41     		/*
     42     		** time_t is integral and unsigned.
     43     		** The difference of two unsigned values can't overflow
     44     		** if the minuend is greater than or equal to the subtrahend.
     45     		*/
     46     		if (time1 >= time0)
     47     			return time1 - time0;
     48     		else	return -((double) (time0 - time1));
     49     	}
     50     	/*
     51     	** time_t is integral and signed.
     52     	** Handle cases where both time1 and time0 have the same sign
     53     	** (meaning that their difference cannot overflow).
     54     	*/
     55     	if ((time1 < 0) == (time0 < 0))
     56     		return time1 - time0;
     57     	/*
     58     	** time1 and time0 have opposite signs.
     59     	** Punt if unsigned long is too narrow.
     60     	*/
     61     	/* CONSTCOND */
     62     	if (sizeof (unsigned long) < sizeof (time_t))
     63     		return (double) time1 - (double) time0;
     64     	/*
     65     	** Stay calm...decent optimizers will eliminate the complexity below.
     66     	*/
     67     	if (time1 >= 0 /* && time0 < 0 */)
     68     		return (unsigned long) time1 +
     69     			(unsigned long) (-(time0 + 1)) + 1;
     70     	return -(double) ((unsigned long) time0 +
     71     		(unsigned long) (-(time1 + 1)) + 1);
     72     }
     73