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File: [cvs.NetBSD.org] / src / lib / libc / time / difftime.c (download)

Revision 1.9, Tue Jan 29 12:58:32 2002 UTC (18 years, 8 months ago) by kleink
Branch: MAIN
CVS Tags: yamt-pf42-baseX, yamt-pf42-base4, yamt-pf42-base3, yamt-pf42-base2, yamt-pf42-base, yamt-pf42, wrstuden-revivesa-base-3, wrstuden-revivesa-base-2, wrstuden-revivesa-base-1, wrstuden-revivesa-base, wrstuden-revivesa, wrstuden-fixsa-newbase, wrstuden-fixsa-base-1, wrstuden-fixsa-base, wrstuden-fixsa, netbsd-5-base, netbsd-5-2-RELEASE, netbsd-5-2-RC1, netbsd-5-2-3-RELEASE, netbsd-5-2-2-RELEASE, netbsd-5-2-1-RELEASE, netbsd-5-2, netbsd-5-1-RELEASE, netbsd-5-1-RC4, netbsd-5-1-RC3, netbsd-5-1-RC2, netbsd-5-1-RC1, netbsd-5-1-5-RELEASE, netbsd-5-1-4-RELEASE, netbsd-5-1-3-RELEASE, netbsd-5-1-2-RELEASE, netbsd-5-1-1-RELEASE, netbsd-5-1, netbsd-5-0-RELEASE, netbsd-5-0-RC4, netbsd-5-0-RC3, netbsd-5-0-RC2, netbsd-5-0-RC1, netbsd-5-0-2-RELEASE, netbsd-5-0-1-RELEASE, netbsd-5-0, netbsd-5, netbsd-4-base, netbsd-4-0-RELEASE, netbsd-4-0-RC5, netbsd-4-0-RC4, netbsd-4-0-RC3, netbsd-4-0-RC2, netbsd-4-0-RC1, netbsd-4-0-1-RELEASE, netbsd-4-0, netbsd-4, netbsd-3-base, netbsd-3-1-RELEASE, netbsd-3-1-RC4, netbsd-3-1-RC3, netbsd-3-1-RC2, netbsd-3-1-RC1, netbsd-3-1-1-RELEASE, netbsd-3-1, netbsd-3-0-RELEASE, netbsd-3-0-RC6, netbsd-3-0-RC5, netbsd-3-0-RC4, netbsd-3-0-RC3, netbsd-3-0-RC2, netbsd-3-0-RC1, netbsd-3-0-3-RELEASE, netbsd-3-0-2-RELEASE, netbsd-3-0-1-RELEASE, netbsd-3-0, netbsd-3, netbsd-2-base, netbsd-2-1-RELEASE, netbsd-2-1-RC6, netbsd-2-1-RC5, netbsd-2-1-RC4, netbsd-2-1-RC3, netbsd-2-1-RC2, netbsd-2-1-RC1, netbsd-2-1, netbsd-2-0-base, netbsd-2-0-RELEASE, netbsd-2-0-RC5, netbsd-2-0-RC4, netbsd-2-0-RC3, netbsd-2-0-RC2, netbsd-2-0-RC1, netbsd-2-0-3-RELEASE, netbsd-2-0-2-RELEASE, netbsd-2-0-1-RELEASE, netbsd-2-0, netbsd-2, netbsd-1-6-base, netbsd-1-6-RELEASE, netbsd-1-6-RC3, netbsd-1-6-RC2, netbsd-1-6-RC1, netbsd-1-6-PATCH002-RELEASE, netbsd-1-6-PATCH002-RC4, netbsd-1-6-PATCH002-RC3, netbsd-1-6-PATCH002-RC2, netbsd-1-6-PATCH002-RC1, netbsd-1-6-PATCH002, netbsd-1-6-PATCH001-RELEASE, netbsd-1-6-PATCH001-RC3, netbsd-1-6-PATCH001-RC2, netbsd-1-6-PATCH001-RC1, netbsd-1-6-PATCH001, netbsd-1-6, nathanw_sa_before_merge, nathanw_sa_base, mjf-devfs2-base, mjf-devfs2, matt-premerge-20091211, matt-nb5-pq3-base, matt-nb5-pq3, matt-nb5-mips64-u2-k2-k4-k7-k8-k9, matt-nb5-mips64-u1-k1-k5, matt-nb5-mips64-premerge-20101231, matt-nb5-mips64-premerge-20091211, matt-nb5-mips64-k15, matt-nb5-mips64, matt-nb4-mips64-k7-u2a-k9b, matt-mips64-base2, matt-mips64-base, matt-mips64, matt-armv6-prevmlocking, matt-armv6-nbase, matt-armv6-base, matt-armv6, keiichi-mipv6-base, keiichi-mipv6, jym-xensuspend-nbase, jym-xensuspend-base, jym-xensuspend, hpcarm-cleanup-nbase, hpcarm-cleanup-base, hpcarm-cleanup, fvdl_fs64_base, cube-autoconf-base, cube-autoconf, christos-time_t-nbase, christos-time_t-base, christos-time_t, abandoned-netbsd-4-base, abandoned-netbsd-4
Changes since 1.8: +10 -4 lines

Delint me harder.

/*	$NetBSD: difftime.c,v 1.9 2002/01/29 12:58:32 kleink Exp $	*/

/*
** This file is in the public domain, so clarified as of
** June 5, 1996 by Arthur David Olson (arthur_david_olson@nih.gov).
*/

#include <sys/cdefs.h>
#if defined(LIBC_SCCS) && !defined(lint)
#if 0
static char	elsieid[] = "@(#)difftime.c	7.9";
#else
__RCSID("$NetBSD: difftime.c,v 1.9 2002/01/29 12:58:32 kleink Exp $");
#endif
#endif /* LIBC_SCCS and not lint */


/*LINTLIBRARY*/

#include "private.h"

/*
** Algorithm courtesy Paul Eggert (eggert@twinsun.com).
*/

#ifdef HAVE_LONG_DOUBLE
#define long_double	long double
#endif /* defined HAVE_LONG_DOUBLE */
#ifndef HAVE_LONG_DOUBLE
#define long_double	double
#endif /* !defined HAVE_LONG_DOUBLE */

double
difftime(time1, time0)
const time_t	time1;
const time_t	time0;
{
	time_t	delta;
	time_t	hibit;

	{
		time_t		tt;
		double		d;
		long_double	ld;

#ifdef __lint__
		/* LINTED unused warning bug */&tt;
		/* LINTED unused warning bug */&d;
		/* LINTED unused warning bug */&ld;
#endif

		if (/* LINTED constant */sizeof tt < sizeof d)
			return (double) time1 - (double) time0;
		if (/* LINTED constant */sizeof tt < sizeof ld)
			return (long_double) time1 - (long_double) time0;
	}
	if (time1 < time0)
		return -difftime(time0, time1);
	/*
	** As much as possible, avoid loss of precision
	** by computing the difference before converting to double.
	*/
	delta = time1 - time0;
	if (delta >= 0)
		return delta;
	/*
	** Repair delta overflow.
	*/
	hibit = (~ (time_t) 0) << (TYPE_BIT(time_t) - 1);
	/*
	** The following expression rounds twice, which means
	** the result may not be the closest to the true answer.
	** For example, suppose time_t is 64-bit signed int,
	** long_double is IEEE 754 double with default rounding,
	** time1 = 9223372036854775807 and time0 = -1536.
	** Then the true difference is 9223372036854777343,
	** which rounds to 9223372036854777856
	** with a total error of 513.
	** But delta overflows to -9223372036854774273,
	** which rounds to -9223372036854774784, and correcting
	** this by subtracting 2 * (long_double) hibit
	** (i.e. by adding 2**64 = 18446744073709551616)
	** yields 9223372036854776832, which
	** rounds to 9223372036854775808
	** with a total error of 1535 instead.
	** This problem occurs only with very large differences.
	** It's too painful to fix this portably.
	** We are not alone in this problem;
	** some C compilers round twice when converting
	** large unsigned types to small floating types,
	** so if time_t is unsigned the "return delta" above
	** has the same double-rounding problem with those compilers.
	*/
	return delta - 2 * (long_double) hibit;
}