56 lines
1.7 KiB
Fortran
56 lines
1.7 KiB
Fortran
|
!
|
||
|
|
! Generate a seed for the RANDOM_NUMBER PRNG that is guaranteed to be
|
||
|
|
! unique even if many processes are started simultaneously
|
||
|
|
!
|
||
|
|
subroutine init_random_seed()
|
||
|
|
use iso_fortran_env, only: int64
|
||
|
|
implicit none
|
||
|
|
integer, allocatable :: seed(:)
|
||
|
|
integer :: i, n, un, istat, dt(8), pid
|
||
|
|
integer(int64) :: t
|
||
|
|
|
||
|
|
call random_seed(size = n)
|
||
|
|
allocate(seed(n))
|
||
|
|
! First try if the OS provides a random number generator
|
||
|
|
open(newunit=un, file="/dev/urandom", access="stream", &
|
||
|
|
form="unformatted", action="read", status="old", iostat=istat)
|
||
|
|
if (istat == 0) then
|
||
|
|
read(un) seed
|
||
|
|
close(un)
|
||
|
|
else
|
||
|
|
! Fallback to XOR:ing the current time and pid. The PID is
|
||
|
|
! useful in case one launches multiple instances of the same
|
||
|
|
! program in parallel.
|
||
|
|
call system_clock(t)
|
||
|
|
if (t == 0) then
|
||
|
|
call date_and_time(values=dt)
|
||
|
|
t = (dt(1) - 1970) * 365_int64 * 24 * 60 * 60 * 1000 &
|
||
|
|
+ dt(2) * 31_int64 * 24 * 60 * 60 * 1000 &
|
||
|
|
+ dt(3) * 24_int64 * 60 * 60 * 1000 &
|
||
|
|
+ dt(5) * 60 * 60 * 1000 &
|
||
|
|
+ dt(6) * 60 * 1000 + dt(7) * 1000 &
|
||
|
|
+ dt(8)
|
||
|
|
end if
|
||
|
|
pid = getpid()
|
||
|
|
t = ieor(t, int(pid, kind(t)))
|
||
|
|
do i = 1, n
|
||
|
|
seed(i) = lcg(t)
|
||
|
|
end do
|
||
|
|
end if
|
||
|
|
call random_seed(put=seed)
|
||
|
|
contains
|
||
|
|
! This simple PRNG might not be good enough for real work, but is
|
||
|
|
! sufficient for seeding a better PRNG.
|
||
|
|
function lcg(s)
|
||
|
|
integer :: lcg
|
||
|
|
integer(int64) :: s
|
||
|
|
if (s == 0) then
|
||
|
|
s = 104729
|
||
|
|
else
|
||
|
|
s = mod(s, 4294967296_int64)
|
||
|
|
end if
|
||
|
|
s = mod(s * 279470273_int64, 4294967291_int64)
|
||
|
|
lcg = int(mod(s, int(huge(0), int64)), kind(0))
|
||
|
|
end function lcg
|
||
|
|
end subroutine init_random_seed
|