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From: "sgk at troutmask dot apl.washington.edu" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug fortran/49010] Result of MOD and MODULO intrinsic has wrong sign
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49010

--- Comment #3 from Steve Kargl <sgk at troutmask dot apl.washington.edu> 2011-05-16 21:17:44 UTC ---
There is an additional problem with MOD(A,P) and MODULO(A,P).

In F95, one finds "P = 0, the result is processor dependent."

In F2003 and F2008, one finds "P shall not be zero."

Consider the code,

program foo
   real, parameter :: b = 0.
   real a, p, m1, m2
   a = 2.
   p = 0.
   m1 = mod(a, p)
   m2 = mod(a, b)
   print *, m1, m2
end program foo

with the __builtin_fmod function we get

troutmask:sgk[215] gfc4x -o z t.f90 && ./z
              NaN              NaN

(ie., there is no error or warning that P=0).

If we simply eliminate the __builtin_fmod function,
we get 

troutmask:sgk[212] gfc4x -o z t.f90 && ./z
   2.00000000       2.00000000    

which is worse than the NaN. :(
__ 
Steve