sinisalo_sieve.f90

! Eratosthenes Sieve
! Prime number < 100 000 000
! Thanks Matti Kalevi Sinisalo
!  Linux simplyfortran
integer nprs
logical prime(100000000)
do i = 1,100000000
    prime(i) = .TRUE.
end  do
loop: do ip=2,10000
    if(.not.prime(ip)) cycle loop
       ! print *,ip
       ! Ei printata suuren lukumäärän takia
    do i=2*ip,100000000,ip
        prime(i)=.FALSE.
    end do
end do loop
nprs=0
do i=2,100000000
    if(prime(i)) nprs=nprs+1
end do
print *,'alle miljardin olevia alkulukuja ',nprs
end