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difftime.c revision 1.10 
      1 /*	$NetBSD: difftime.c,v 1.10 2009/12/31 22:49:16 mlelstv 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 2009/12/31 22:49:16 mlelstv 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(time1, time0)
     23 const time_t	time1;
     24 const time_t	time0;
     25 {
     26 	/*
     27 	** If (sizeof (double) > sizeof (time_t)) simply convert and subtract
     28 	** (assuming that the larger type has more precision).
     29 	** This is the common real-world case circa 2004.
     30 	*/
     31 /* LINTED constant */
     32 	if (sizeof (double) > sizeof (time_t))
     33 		return (double) time1 - (double) time0;
     34 /* LINTED constant */
     35 	if (!TYPE_INTEGRAL(time_t)) {
     36 		/*
     37 		** time_t is floating.
     38 		*/
     39 		return time1 - time0;
     40 	}
     41 /* LINTED constant */
     42 	if (!TYPE_SIGNED(time_t)) {
     43 		/*
     44 		** time_t is integral and unsigned.
     45 		** The difference of two unsigned values can't overflow
     46 		** if the minuend is greater than or equal to the subtrahend.
     47 		*/
     48 		if (time1 >= time0)
     49 			return time1 - time0;
     50 		else	return -((double) (time0 - time1));
     51 	}
     52 	/*
     53 	** time_t is integral and signed.
     54 	** Handle cases where both time1 and time0 have the same sign
     55 	** (meaning that their difference cannot overflow).
     56 	*/
     57 	if ((time1 < 0) == (time0 < 0))
     58 		return time1 - time0;
     59 	/*
     60 	** time1 and time0 have opposite signs.
     61 	** Punt if unsigned long is too narrow.
     62 	*/
     63 /* CONSTCOND */
     64 	if (sizeof (unsigned long) < sizeof (time_t))
     65 		return (double) time1 - (double) time0;
     66 	/*
     67 	** Stay calm...decent optimizers will eliminate the complexity below.
     68 	*/
     69 	if (time1 >= 0 /* && time0 < 0 */)
     70 		return (unsigned long) time1 +
     71 			(unsigned long) (-(time0 + 1)) + 1;
     72 	return -(double) ((unsigned long) time0 +
     73 		(unsigned long) (-(time1 + 1)) + 1);
     74 }
     75