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difftime.c revision 1.15 
      1     /*	$NetBSD: difftime.c,v 1.15 2013/09/20 19:06:54 christos 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 1.15 2013/09/20 19:06:54 christos Exp $");
     14     #endif
     15     #endif /* LIBC_SCCS and not lint */
     16     
     17     /*LINTLIBRARY*/
     18     
     19     #include "private.h"	/* for time_t and TYPE_SIGNED */
     20     
     21     double ATTRIBUTE_CONST
     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     	*/
     28     	/*CONSTCOND*/
     29     	if (sizeof (double) > sizeof (time_t))
     30     		return (double) time1 - (double) time0;
     31     	/*LINTED const not */
     32     	if (!TYPE_SIGNED(time_t)) {
     33     		/*
     34     		** The difference of two unsigned values can't overflow
     35     		** if the minuend is greater than or equal to the subtrahend.
     36     		*/
     37     		if (time1 >= time0)
     38     			return            time1 - time0;
     39     		else	return -(double) (time0 - time1);
     40     	}
     41     	/*
     42     	** Handle cases where both time1 and time0 have the same sign
     43     	** (meaning that their difference cannot overflow).
     44     	*/
     45     	if ((time1 < 0) == (time0 < 0))
     46     		return time1 - time0;
     47     	/*
     48     	** time1 and time0 have opposite signs.
     49     	** Punt if uintmax_t is too narrow.
     50     	** This suffers from double rounding; attempt to lessen that
     51     	** by using long double temporaries.
     52     	*/
     53     	/* CONSTCOND */
     54     	if (sizeof (uintmax_t) < sizeof (time_t))
     55     		return (double) time1 - (double) time0;
     56     	/*
     57     	** Stay calm...decent optimizers will eliminate the complexity below.
     58     	*/
     59     	if (time1 >= 0 /* && time0 < 0 */)
     60     		return    (uintmax_t) time1 + (uintmax_t) (-(time0 + 1)) + 1;
     61     	return -(double) ((uintmax_t) time0 + (uintmax_t) (-(time1 + 1)) + 1);
     62     }
     63