Re: Problem with source.f

From: Joseph Comfort (Joseph.Comfort@asu.edu)
Date: Sat Nov 04 2006 - 19:51:11 CET

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    Dear Chris,

    Thank you for your helpful and insightful comments. You are certainly
    correct about the IEEE754 standard, and the need to be careful about
    compiler options. On my 64-bit Opteron machine, the C 'sizeof' command
    gives 4 bytes for float, and 8 bytes for double, just as for a 32-bit
    machine. These can be modified, however, by compiler options.
    According to the information on the gcc (g77/gfortran) compiler, the
    '-m64' option sets 'int' variables to 32 bits (8 bytes) and 'long'
    variables to 64 bits (16 bytes). ((It doesn't say what happens to
    doubles.) -m64 is normally the default in most Linux distributions on
    64-bit machines, and -m32 is needed to restore the standard sizes. This
    difference from 32-bit machines led to numerous problems in compiling
    Geant3.

    A couple of interesting web links on these issues are:
      http://www.network-theory.co.uk/docs/gccintro/gccintro_70.html
      http://developers.sun.com/sunstudio/articles/fp_errors.html

    Best regards,
    Joe

    -- 
    Joseph Comfort                      Phone: (480)-965-6377
    Department of Physics & Astronomy   Dept.: (480)-965-3561
    Arizona State University            Fax:   (480)-965-7954
    Tempe, AZ  85287-1504               Email: Joseph.Comfort@asu.edu
    

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