------- Comment #5 from burnus at gcc dot gnu dot org 2006-11-02 16:02 -------
Created an attachment (id=12535)
--> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=12535&action=view)
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
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28484
