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difftime.c revision 1.10.6.1 
      1 /*	$NetBSD: difftime.c,v 1.10.6.1 2012/04/17 00:05:26 yamt 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 1.10.6.1 2012/04/17 00:05:26 yamt 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 /* LINTED constant */
     30 	if (sizeof (double) > sizeof (time_t))
     31 		return (double) time1 - (double) time0;
     32 /* LINTED constant */
     33 	if (!TYPE_INTEGRAL(time_t)) {
     34 		/*
     35 		** time_t is floating.
     36 		*/
     37 		return time1 - time0;
     38 	}
     39 /* LINTED constant */
     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