[Bug fortran/37832] New: System_Clock

[Bug fortran/37832] New: System_Clock

[DavidLNewton at yahoo dot com]

Resolution of the System_Clock(TICKS,RATE,MAX) intrinsic degraded from about
3.6 MHz to 1,000 Hz when I upgraded from g77 to gfortran (for Windows).

There is a computer clock that I have accessed in Visual Basic that represents
elapsed time since my computer was turned on, returned as an integer*8
quantity, which operates at the higher frequency.

It should be possible for you to offer something similar by re-writing
System_Clock(TICKS,RATE,MAX) to operate at the higher frequency (as it was in
g77) and return TICKS as an integer*8.


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           Summary: System_Clock
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: DavidLNewton at yahoo dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37832

[Bug fortran/37832] System_Clock

[kargl at gcc dot gnu dot org]

------- Comment #1 from kargl at gcc dot gnu dot org  2008-10-15 05:50 -------
You can already get an integer(8) result.

integer(8) ticks,rate
call system_clock(count=ticks,count_rate=rate)
print *, ticks, rate
end

gfc -o z a.f90
./z
           2131173368                 1000

count_rate is determined from either /usr/include/sys/time.h or
/usr/include/time.h.  You need to munge your system header files.

For the record, there is very little OS specific code in the
library, and I would actively oppose putting more OS specific code
in the library.  If you want higher resolution try cpu_time, which
is one of the few routines that has OS specific code.

You can also write your timing routine in C and use ISO C binding
to call that routine.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37832

[Bug fortran/37832] System_Clock

[burnus at gcc dot gnu dot org]

------- Comment #2 from burnus at gcc dot gnu dot org  2008-10-15 06:33 -------
See also PR 28484 comment 5.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37832

[Bug fortran/37832] System_Clock

[jvdelisle at gcc dot gnu dot org]

------- Comment #3 from jvdelisle at gcc dot gnu dot org  2008-11-03 02:17 -------
I will add this to my list and see if we can get to what g77 does.


-- 

jvdelisle at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |jvdelisle at gcc dot gnu dot
                   |dot org                     |org
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2008-11-03 02:17:47
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37832

[Bug fortran/37832] System_Clock

[jvdelisle at gcc dot gnu dot org]

------- Comment #4 from jvdelisle at gcc dot gnu dot org  2008-11-09 07:46 -------
According to the g77 documentation, system_clock uses the times(2) function.

gfortran uses either the time(2) (note no 's' on the end of the name) or the
gettimeofday function.  When I revise the gfortran routines to use the times(2)
function I get results similar to g77.

Now question is, how equivalent to g77 do we want to get in this case?


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37832

[Bug fortran/37832] System_Clock

[jvdelisle at gcc dot gnu dot org]

------- Comment #5 from jvdelisle at gcc dot gnu dot org  2008-11-09 18:18 -------
After doing some more testing and comparing g77 vs gfortran, gfortran actually
provides higher resolution 1000 ticks/sec then g77 100 ticks/second on at least
my platform (x86-64-linux) On Cygwin, results are identical except gfortran
does allow integer(kind=8) where g77 does not.

Therefore, I am closing this as "not a bug".  If greater timing precision is
needed, then Steve's suggestion of binding to a custom C routine is the wy to
go.


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jvdelisle at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |WORKSFORME


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37832