Recently, I wrote a piece of codes, like that below. The value of num is larger than the range of integer 32.
The result of the tmp should be 2. But in that code, the program gave 0. No matter if use ifort 13.0.0 or 15.0.0. If I change the tmp from real*4 to real*8, the result is correct. Ang idea?
integer*8,parameter :: num = 2500000000
integer*8 :: i
real*4,dimension(:),allocatable :: a
real*4 :: tmp
allocate(a(num))
a = 0.0e0
do i = 1, num
if(i.eq.1) then
a(1) = 1.0e0
else if(mod(i, 2).eq.0) then
a(i) = 1.0e0
else
a(i) = -1.0e0
end if
end do
tmp = 0.0e0
do i = 1, num
tmp = tmp + a(i)
end do
print*, tmp
end