Bug 28484

gfortran is primarily a Fortran 95 with a few Fortran 2003 enhancements.

Confirmed.

Subject: Bug number PR28484

A patch for this bug has been added to the patch tracker.
The mailing list url for the patch is http://gcc.gnu.org/ml/gcc-patches/2006-10/msg01387.html

Assign.

Preliminary patch at:
http://gcc.gnu.org/ml/gcc-patches/2006-10/msg01387.html

Created attachment 12535 [details]
Idea how libgfortran/intrinsic/system_clock.c could look like

Some bits of thought.

Methods obtaining the time:
* clock_gettime() [POSIX]
  10^-9s (nanosecond) resolution, options:
  CLOCK_REALTIME  - on unix time since the epoch [I would suggested this]
  CLOCK_MONOTONIC - survives even changing the time,
     but starting point is arbitrary
  See also PR 15516 for assembler calling sequences for Linux

* gettimeofday (&tv, NULL) [POSIX]
  10^-6s (microsecond) resolution

* time() [POSIX]
  second resolution


Resolution -> time able to be represented
---------------------------------------------
For huge(i4) = 2147483647
1000 ms:    68 years
 100 ms:  2485 days
  10 ms:   246 days
   1 ms:    25 days
 100 us:    60 hours
  10 us:     6 hours
=> 10 ms seems to be a good resolution, 25 days might be a bit short for some calculation jobs, but 250 days should be enough.

For huge(i8) = 9223372036854775807
1  s:      2e11 years
1 ms:      2e8  years
1 us: 292271    years
1 ns:    292    years
=> 1 ns seems to be ok

I'm thinking of the following library implementation:
Only do integer(8) as this seems to be enough. (See attachment.)

For iresolve.c one needs to do something like the following (pseudo code):

if(count != NULL && counts.type != 8)
  gfc_convert_type()
if(count != NULL && count_max.type != 8)
  gfc_convert_type()
if(count != NULL && count_rate.type != 8)
  gfc_convert_type()

c->resolved_sym = gfc_get_intrinsic_sub_symbol ("system_clock")

if (count != NULL && count.type == 4)
   count = (int4) ((count8/10000000) % GFC_INTEGER_4_HUGE)
else if (count != NULL && count.type != 8)
   count = (type) count8

if (count_rate != NULL && count_rate.type == 4)
   add_expression("if(count_rate8 == 0) count_rate = 0"
                  "else count_rate = 100")
else if (count != NULL && count.type != 8)
   count_rate = (type) count_rate8

if (count_max != NULL && count_max.type == 4)
   add_expression("if(count_max8 == 0) count_max = 0"
                  "else count_max = GFC_INTEGER_4_HUGE")
else if (count != NULL && count.type != 8)
   count_rate = (type) count_rate8

Created attachment 12536 [details]
Revised idea how libgfortran/intrinsic/system_clock.c could look like

The latter part is of cause not completely right if count_rate = 1 or 1000000, and for an error int16 and real counts didn't contain -huge().

Maybe having in the library a system_clock_4 version makes life easier.

The following pseudocode should then work with system_clock_4 and system_clock_8 (which has also the advantage that we don't modify the library which is nice in terms of compatibility :-)

if ( (counts != NULL && counts.type == 4)
   ||(count_max != NULL && count_max.type == 4) {
  if(count != NULL && counts.type != 4)
    gfc_convert_type()
  if(count != NULL && count_max.type != 4)
    gfc_convert_type()
  if(count != NULL && count_rate.type != 4)
    gfc_convert_type()

  c->resolved_sym = gfc_get_intrinsic_sub_symbol ("system_clock_4")

  if (counts != NULL && counts.type != 4)
    add_expression("if(counts4 < 0) counts = -huge_max(type)"
                   "else counts = (type) counts4")
  if (count_rate != NULL && count_rate.type != 4)
    count_rate = (type) count_rate4

  if (count_max != NULL && count_max.type != 4)
    count_rate = (type) count_rate4
} else {
  if(count != NULL && counts.type != 8)
    gfc_convert_type()
  if(count != NULL && count_max.type != 8)
    gfc_convert_type()
  if(count != NULL && count_rate.type != 8)
    gfc_convert_type()

  c->resolved_sym = gfc_get_intrinsic_sub_symbol ("system_clock_8")

  if (counts != NULL && counts.type != 8)
    add_expression("if(counts8 < 0) counts = -huge_max(type)"
                   "else counts = (type) counts8")
  if (count_rate != NULL && count_rate.type != 8)
    count_rate = (type) count_rate8

  if (count_max != NULL && count_max.type != 8)
    count_rate = (type) count_rate8
}

Now I only have to figure out how to add the conversion and the "if(counts8 < 0)" expression in iresolve.c.

Won't work on it for a while.

Taking over.

(In reply to comment #8)
> Taking over.
> 

Any news on this ?

(In reply to comment #9)
> Any news on this ?

Bad ones. Lost track due to real-life interference. 
Unassigning myself for now.

Raising this up a little since F2003 features are coming up

Since the actual implementation of system_clock has no use for non-integer count rates, this should be implemented by creating an integer temporary in the frontend and then calling the existing functions.

Also, note that as of r155359 the integer(8) version of system_clock now provides microsecond resolution. In the future, this could be improved further by switching to using clock_gettime(CLOCK_MONOTONIC,...) which in addition to providing better resolution also gives a monotonic clock instead of a realtime clock that gettimeofday() gives.

Author: fxcoudert
Date: Sun Jun 15 16:58:53 2014
New Revision: 211686

URL: https://gcc.gnu.org/viewcvs?rev=211686&root=gcc&view=rev
Log:
	PR fortran/28484
	PR fortran/61429

	* check.c (gfc_check_system_clock): Improve checking of arguments.
	* intrinsic.texi: Update doc of SYSTEM_CLOCK.
	* iresolve.c (gfc_resolve_system_clock): Choose library function
	used depending on argument kinds.
	* trans-decl.c (gfc_build_intrinsic_function_decls): Build
	decls for system_clock_4 and system_clock_8.
	* trans-intrinsic.c (conv_intrinsic_system_clock): New function.
	(gfc_conv_intrinsic_subroutine): Call conv_intrinsic_system_clock.
	* trans.h (gfor_fndecl_system_clock4, gfor_fndecl_system_clock8):
	New variables.

	* gfortran.dg/system_clock_1.f90: New file.
	* gfortran.dg/system_clock_2.f90: New file.

Added:
    trunk/gcc/testsuite/gfortran.dg/system_clock_1.f90
    trunk/gcc/testsuite/gfortran.dg/system_clock_2.f90
Modified:
    trunk/gcc/fortran/ChangeLog
    trunk/gcc/fortran/check.c
    trunk/gcc/fortran/intrinsic.texi
    trunk/gcc/fortran/iresolve.c
    trunk/gcc/fortran/trans-decl.c
    trunk/gcc/fortran/trans-intrinsic.c
    trunk/gcc/fortran/trans.h
    trunk/gcc/testsuite/ChangeLog

Fixed on trunk (4.10).