XL Fortran for AIX 8.1
This chapter answers some common questions about floating-point processing,
- How can I get predictable, consistent results?
- How can I get the fastest or the most accurate results?
- How can I detect, and possibly recover from, exception conditions?
- What are the purposes of some of the less-frequently used compiler
- Related Information:
This chapter makes frequent reference to the compiler options that are grouped
together in Options for Floating-Point Processing, especially -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 in the XL Fortran for AIX Language
Reference 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 chapter before using these options.
- The discussions of single-, double-, and extended-precision calculations in
this chapter 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
Most of the information in this chapter relates to floating-point
processing on the PowerPC family of processors. The section Floating-Point Processing on the POWER and POWER2 Architectures describes the differences between floating-point processing
on the PowerPC processors and floating-point processing on the POWER and
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