! compile as: gfortran -O2 sumj.f
! try also the option -march=native 
        program sumj
        implicit none
        integer, parameter :: Prec=8
        integer(8) ::  j,N,base,p0,p1,power
        real(8) :: t0,t1,t
        real(Prec) ::  x
        character(3) :: sprec
        character(100) :: f_out,shost
! Preparations
        write(sprec,'(I3)') Prec
        call HOSTNM(shost) !get computer name
! make a file name for output
        f_out=trim(adjustl(sprec))//"_"//trim(adjustl(shost))//".dat0"
! Collect system info and write that to a file
        call system("bash sys_info.sh "//f_out)
! Actual calculation
        base=2
        p0=10
        p1=34
        open(1,file=f_out,position="append")
        
        do power= p0,p1
           N= base**power
           x= real(0.,Prec)
           call cpu_time(t0)
                do j= -N,N
                   x=x + real(j,Prec)
                end do
           call cpu_time(t1)
           t=t1-t0
           write(1,*) power,N,x,kind(x),t
           write(*,*) power,N,x,kind(x),t
        enddo
         
        close(1)
        end program