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From: "steven.vancoillie at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/52884] New: double precision constants promoted to 16 byte by -fdefault-real-8
Date: Thu, 05 Apr 2012 21:51:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52884

             Bug #: 52884
           Summary: double precision constants promoted to 16 byte by
                    -fdefault-real-8
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: steven.vancoillie@gmail.com


Contrary to what the man pages say, double precision constants like '1.d0' get
promoted to 16 bytes when using -fdefault-real-8 (without -fdefault-double-8). 
The man pages at the section of -fdefault-double-8 say however that
-fdefault-real-8 does not promote constants like that.  Is this an error in the
man pages?

>>From the man pages:

-fdefault-double-8
           Set the "DOUBLE PRECISION" type to an 8 byte wide type.
           If -fdefault-real-8 is given, "DOUBLE PRECISION" would instead be
           promoted to 16 bytes if possible, and -fdefault-double-8 can be used
           to prevent this.  The kind of real constants like "1.d0" will not be
           changed by -fdefault-real-8 though, so also -fdefault-double-8 does
           not affect it.

Using e.g. the following program:

program doubletrouble
real*8 x
double precision y
write(*,*) kind(x), kind(y), kind(1.d0)
end

Compiling without any options gives '8 8 8' as output.  Compiling with
-fdefault-real-8 gives '8 16 16', while I expected it to be '8 16 8' based on
the documentation.

This is with gfortran 4.7.0 on Linux x86_64 (Intel Core i5 M 540)