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difftime.c revision 1.11.2.2 
      1 /*	$NetBSD: difftime.c,v 1.11.2.2 2014/08/20 00:02:16 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 1.11.2.2 2014/08/20 00:02:16 tls 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