test_div.f90

! This is not a bug, but the result is surprising.
! See https://fortran-lang.discourse.group/t/strange-behavior-of-ifort
! See also test_intel_sym.f90.
!--------------------------------------------------------------------------------------------------!
! $ uname -a && ifort --version && ifort test_div.f90 && ./a.out
! Linux zP 5.15.0-52-generic #58-Ubuntu SMP Thu Oct 13 08:03:55 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
!
! ifort (IFORT) 2021.7.1 20221019
! Copyright (C) 1985-2022 Intel Corporation.  All rights reserved.
!
! Before division, x =    1.000000       1.000000       1.000000     1.000000       1.000000
! All entries of x are identical? T
! After division, x =   0.9999999      0.9999999      0.9999999    0.9999999       1.000000
! i =            1 x(1) == x(i)? T
!111110101010101010101010101010 111110101010101010101010101010
! i =            2 x(1) == x(i)? T
!111110101010101010101010101010 111110101010101010101010101010
! i =            3 x(1) == x(i)? T
!111110101010101010101010101010 111110101010101010101010101010
! i =            4 x(1) == x(i)? T
!111110101010101010101010101010 111110101010101010101010101010
! i =            5 x(1) == x(i)? F
!111110101010101010101010101010 111110101010101010101010101011
!
! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
! !!!!!!!!!!! Surprise! x(1) is different from x(i) !!!!!!!!!
! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!--------------------------------------------------------------------------------------------------!

program test
implicit none

integer :: i
real :: x(5)
x = 1.0  ! All elements of x are set to the same value.
print *, 'Before division, x = ', x
print *, 'All entries of x are identical?', all(x == x(1))
x = x / x(1)  ! OR: x = x / 3.0
print *, 'After division, x = ', x
do i = 1, size(x)
    print *, 'i = ', i, 'x(1) == x(i)?', x(1) == x(i)

    print "(*(b0,1x))", x(1), x(i)

    if (x(1) /= x(i)) then
        print *, ''
        print *, '!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!'
        print *, '!!!!!!!!!!! Surprise! x(1) is different from x(i) !!!!!!!!!'
        print *, '!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!'
        print *, ''
    end if
end do

end program test