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58 lines
1.7 KiB
C
58 lines
1.7 KiB
C
/*-*- mode:c;indent-tabs-mode:t;c-basic-offset:8;tab-width:8;coding:utf-8 -*-│
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│ vi: set noet ft=c ts=8 sw=8 fenc=utf-8 :vi │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/calls/weirdtypes.h"
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#include "libc/macros.h"
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#include "libc/time.h"
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/* Return the difference between two timestamps. */
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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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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 : dminus(time0 - time1);
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/* Use uintmax_t if wide enough. */
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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(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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