66 lines
1.7 KiB
C
66 lines
1.7 KiB
C
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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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#ifndef lint
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#ifndef NOID
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static char elsieid[] = "@(#)difftime.c 7.19";
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#endif /* !defined NOID */
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#endif /* !defined lint */
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/*LINTLIBRARY*/
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#include "private.h" /* for time_t, TYPE_INTEGRAL, and TYPE_SIGNED */
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double
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difftime(time1, time0)
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const time_t time1;
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const time_t time0;
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{
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/*
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** If (sizeof (double) > sizeof (time_t)) simply convert and subtract
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** (assuming that the larger type has more precision).
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** This is the common real-world case circa 2004.
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*/
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if (sizeof (double) > sizeof (time_t))
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return (double) time1 - (double) time0;
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if (!TYPE_INTEGRAL(time_t)) {
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/*
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** time_t is floating.
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*/
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return time1 - time0;
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}
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if (!TYPE_SIGNED(time_t)) {
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/*
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** time_t is integral and unsigned.
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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 (time1 >= time0)
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return time1 - time0;
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else return -((double) (time0 - time1));
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}
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/*
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** time_t is integral and signed.
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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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** time1 and time0 have opposite signs.
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** Punt if unsigned long is too narrow.
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*/
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if (sizeof (unsigned long) < sizeof (time_t))
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return (double) time1 - (double) time0;
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/*
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** Stay calm...decent optimizers will eliminate the complexity below.
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*/
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if (time1 >= 0 /* && time0 < 0 */)
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return (unsigned long) time1 +
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(unsigned long) (-(time0 + 1)) + 1;
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return -(double) ((unsigned long) time0 +
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(unsigned long) (-(time1 + 1)) + 1);
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}
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