75 lines
1.8 KiB
C
75 lines
1.8 KiB
C
/* $NetBSD: difftime.c,v 1.22 2019/04/04 19:25:38 christos Exp $ */
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/* Return the difference between two timestamps. */
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/*
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** This file is in the public domain, so clarified as of
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** 1996-06-05 by Arthur David Olson.
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*/
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#include <sys/cdefs.h>
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#if defined(LIBC_SCCS) && !defined(lint)
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#if 0
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static char elsieid[] = "@(#)difftime.c 8.1";
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#else
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__RCSID("$NetBSD: difftime.c,v 1.22 2019/04/04 19:25:38 christos Exp $");
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#endif
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#endif /* LIBC_SCCS and not lint */
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/*LINTLIBRARY*/
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#include "private.h" /* for time_t and TYPE_SIGNED */
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/* Return -X as a double. Using this avoids casting to 'double'. */
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static double
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dminus(double x)
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{
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return -x;
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}
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double
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difftime(time_t time1, time_t time0)
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{
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/*
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** If double is large enough, simply convert and subtract
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** (assuming that the larger type has more precision).
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*/
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/*CONSTCOND*/
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if (sizeof (time_t) < sizeof (double)) {
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double t1 = time1, t0 = time0;
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return t1 - t0;
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}
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/*
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** The difference of two unsigned values can't overflow
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** if the minuend is greater than or equal to the subtrahend.
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*/
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if (!TYPE_SIGNED(time_t))
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return time0 <= time1 ? time1 - time0 :
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dminus((double)(time0 - time1));
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/* Use uintmax_t if wide enough. */
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/*CONSTCOND*/
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if (sizeof (time_t) <= sizeof (uintmax_t)) {
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uintmax_t t1 = time1, t0 = time0;
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return time0 <= time1 ? t1 - t0 : dminus((double)(t0 - t1));
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}
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/*
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** Handle cases where both time1 and time0 have the same sign
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** (meaning that their difference cannot overflow).
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*/
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if ((time1 < 0) == (time0 < 0))
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return time1 - time0;
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/*
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** The values have opposite signs and uintmax_t is too narrow.
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** This suffers from double rounding; attempt to lessen that
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** by using long double temporaries.
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*/
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{
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long double t1 = time1, t0 = time0;
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return t1 - t0;
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}
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}
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