Daniel J. Bernstein's hash algorithm written in Fortran

djb_hash.f90

integer function djb_hash(str) result(hash)
    implicit none
    
    character(len=*),intent(in) :: str
    integer :: hash
    integer :: i

    hash = 5381

    do i=1,len(str)
        hash = (ishft(hash,5) + hash) + ichar(str(i:i))
    end do

end function DJB_hash

I actually tried this and you still get hash collisions under certain circumstances:

 ### hash of text "IO" :    615763273
 ### hash of text "INA":    615763273

I think that by the nature of hashing, there will always be cases where collisions occur. You will probably always need some kind of "tiebreaker" algorithm to resolve collisions.