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Subject: [Bug libfortran/49336] New: ATAN2  values differ from those specified in documentation
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49336

           Summary: ATAN2  values differ from those specified in
                    documentation
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: libfortran
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: ahn567@gmail.com


The documentation for ATAN2(Y,X) says:  

"If Y is zero, then the return value is zero if X is positive and pi if X is
negative."

However, the value returned by  ATAN2(-0d0, -1d0)  is  -pi  (not +pi).
This is for gfortran 4.4.5.

So either the documentation needs fixing (and signed zero explained), 
or the function ATAN2 should be redefined to return values in (-pi,pi]. 

...I'm not sure which is more standard for Fortran.