COUNT_RATE and COUNT_MAX of SYSTEM_CLOCK() in Fortran

00Fortran_system_clock.md

COUNT_RATE and COUNT_MAX of SYSTEM_CLOCK() in Fortran

In Fortran, SYSTEM_CLOCK() internal subroutine is commonly used for timing. However, on some platforms, it is difficult to measure a time interval longer than one day, bucause the counter is reset once a day.

Here is a list of COUNT_RATE and COUNT_MAX from CALL SYSTEM_CLOCK(COUNT, COUNT_RATE, COUNT_MAX) on various platforms.

Platform	COUNT_RATE	COUNT_MAX
Linux 2.6.32 with gfortran 4.9.0	1000	2147483647
Mac OS X 10.9.4 with gfortran 4.8.2	1000	2147483647
SR16000: AIX 7.1 with XL Fortran 14.01	100	8639999
FX10: Linux 2.6 with frtpx 1.2.1	1000	86399999

cf. 2**31=2147483648, 1 day = 86400 second

On SR16000, it seems that the counter of system_clock starts at 00:00:00 of local time. What will happen when they do intercalation of a leap second?

Gist

This document is placed at https://gist.github.com/t-nissie/991dba9fd80b56f35e9f . You can clone it with git clone https://gist.github.com/991dba9fd80b56f35e9f.git system_clock or git clone git@gist.github.com:991dba9fd80b56f35e9f.git system_clock.

Makefile

# -*-Makefile-*-
##
MD = 00Fortran_system_clock.md
all: index.html
index.html: $(MD)
	gfm2html.rb --readme -l ja -n 'Takeshi Nishimatsu' -s style.css $(MD) > $@
clean:
	rm -f index.html

style.css

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