fortran - Floating point numbers equality -

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i using gfortran in mingw under windows 7 (32bit) compile fortran 77 code. here minimal code contained in testequal.f file:

  program testequal   real*8 a1, a2    a1 = 0.3d0   a2 = 0.7d0    write(*,*) 1.d0   write(*,*) a1+a2   write(*,*) a1+a2.eq.1.0   write(*,*) a1+a2.eq.1.d0   end

compile with

gfortran testequal.f -std=legacy

the output is:

1.0000000000000000 1.0000000000000000 f f

but expect 2 booleans both t. problem here?

with rare exceptions, don't compare floating point numbers exact equality. rules of finite-precision floating point arithmetic not same rules of real number arithmetic. compare numbers tolerance, e.g., 

sum = a1 + a2 if ( abs (sum - 1.0) < 1.0d-5 ) ...

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