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/*
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/*
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* R : A Computer Language for Statistical Data Analysis
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* R : A Computer Language for Statistical Data Analysis
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* Copyright (C) 2000-2015 The R Core Team.
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* Copyright (C) 2000-2016 The R Core Team.
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*
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*
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* This program is free software; you can redistribute it and/or modify
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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* (at your option) any later version.
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/*
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/*
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Notes on various time functions:
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Notes on various time functions:
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===============================
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===============================
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The current (2008) POSIX recommendation to find the calendar time
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The current (2008/13) POSIX recommendation to find the calendar
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is to call clock_gettime(), defined in <time.h>. This may also be
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time is to call clock_gettime(), defined in <time.h>. This may
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used to find time since some unspecified starting point
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also be used to find the time since some unspecified starting
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(e.g. machine reboot), but is not currently so used in R. It
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point (e.g. machine reboot), but is not currently so used in R.
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returns in second and nanoseconds, although not necessarily to
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It returns in second and nanoseconds, although not necessarily to
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more than clock-tick accuracy.
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more than clock-tick accuracy.
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C11 adds 'struct timespec' to <time.h>. And timespec_get() can get
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C11 adds 'struct timespec' to <time.h>. And timespec_get() which
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the current time or interval after a base time.
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can get the current time or interval after a base time.
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The previous POSIX recommendation was gettimeofday(), defined in
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The previous POSIX recommendation was gettimeofday(), defined in
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<sys/time.h>. This returns in seconds and microseconds (with
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<sys/time.h>. This returns in seconds and microseconds (with
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unspecified granularity).
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unspecified granularity).
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Many systems (including AIX, FreeBSD, Linux, Solaris) have
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Many systems (including AIX, FreeBSD, Linux, Solaris) have
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clock_gettime(). macOS and Cygwin have gettimeofday().
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clock_gettime(): it appeared in macOS 10.12. macOS and Cygwin
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have gettimeofday().
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Function time() is C99 and defined in <time.h>. C99 does not
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Function time() is C99 and defined in <time.h>. C99 does not
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mandate the units, but POSIX does (as the number of seconds since
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mandate the units, but POSIX does (as the number of seconds since
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the epoch: although not mandated, time_t seems always to be an
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the epoch: although not mandated, time_t seems always to be an
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integer type).
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integer type).
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returns the same time structure as gettimeofday() and on some
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returns the same time structure as gettimeofday() and on some
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systems offers millisecond resolution.
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systems offers millisecond resolution.
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It is available on Cygwin, FreeBSD, macOS, Linux and Solaris.
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It is available on Cygwin, FreeBSD, macOS, Linux and Solaris.
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currentTime() (in this file) uses
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currentTime() (in this file) uses
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clock_gettime(): AIX, FreeBSD, Linux, Solaris
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clock_gettime(): AIX, FreeBSD, Linux, Solaris, macOS >= 10.12
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gettimeofday(): macOS, Windows, Cygwin
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gettimeofday(): macOS <= 10.11, Windows, Cygwin
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time() (as ultimate fallback, AFAIK unused).
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time() (as ultimate fallback, AFAIK unused).
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proc.time() uses currentTime() for elapsed time,
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proc.time() uses currentTime() for elapsed time,
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and getrusage, then times for CPU times on a Unix-alike,
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and getrusage, then times for CPU times on a Unix-alike,
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GetProcessTimes on Windows.
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GetProcessTimes on Windows.
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