This section answers some common questions about floating-point processing,
such as:
This section makes frequent reference
to the compiler options that are grouped together in
Options for floating-point processing, especially the
-qfloat option. The XL Fortran compiler also provides three intrinsic modules for exception
handling and IEEE arithmetic support to help you write IEEE module-compliant
code that can be more portable. See
IEEE Modules
and Support for details.
The use of the compiler options for floating-point calculations affects
the accuracy, performance, and possibly the correctness of floating-point
calculations. Although the default values for the options were chosen to provide
efficient and correct execution of most programs, you may need to specify
nondefault options for your applications to work the way you want. We strongly
advise you to read this section before using these options.
The discussions of single-, double-, and extended-precision
calculations in this section all refer to the default situation, with
-qrealsize=4 and no
-qautodbl specified. If you change these
settings, keep in mind that the size of a Fortran
REAL,
DOUBLE
PRECISION, and so on may change, but single precision, double precision,
and extended precision (in lowercase) still refer to 4-, 8-, and 16-byte entities
respectively.
The information in this section relates to floating-point
processing on the PowerPC family of processors.