XL Fortran Enterprise Edition for AIX : User's Guide - IBM

call fpgets(fpstat)
fpstat(fpox) = .FALSE.
call fpsets(fpstat) ! resetting fpstat(fpox) to .FALSE.
Sample Programs for Exception Handling
/usr/lpp/xlf/samples/floating_point contains a number of sample programs to
illustrate different aspects of exception handling:
flttrap_handler.c and flttrap_test.f
A sample exception handler that is written in C
and a Fortran program that uses it.
xl__ieee.F and xl__ieee.c
Exception handlers that are written in Fortran and
C that show how to substitute particular values for
operations that produce exceptions. Even when
you use support code such as this, the
implementation of XL Fortran exception handling
does not fully support the exception-handling
environment that is suggested by the IEEE
floating-point standard.
check_fpscr.f and postmortem.f
Show how to work with the fpsets and fpgets
procedures and the fpstats array.
fhandler.F
xl__trbk_test.f
Shows a sample Fortran signal handler and
demonstrates the xl__sigdump procedure.
Shows how to use the xl__trbk procedure to
generate a traceback listing without stopping the
program.
The sample programs are strictly for illustrative purposes only.
Causing Exceptions for Particular Variables
To mark a variable as “do not use”, you can encode a special value called a
signaling NaN in it. This causes an invalid exception condition any time that
variable is used in a calculation.
If you use this technique, use the nans suboption of the -qfloat option, so that the
program properly detects all cases where a signaling NaN is used, and one of the
methods already described to generate corresponding SIGFPE or SIGTRAP
signals.
Notes:
1. Because a signaling NaN is never generated as the result of a calculation and
must be explicitly introduced to your program as a constant or in input data,
you should not need to use this technique unless you deliberately use signaling
NaN values in it.
2. In previous XL Fortran releases, the -qfloat suboption was called spnans. In the
future, use nans instead (although spnans still works, for backward
compatibility).
Minimizing the Performance Impact of Floating-Point
Exception Trapping
If you need to deal with floating-point exception conditions but are concerned that
doing so will make your program too slow, here are some techniques that can help
minimize the performance impact:
302 XL Fortran Enterprise Edition for AIX : User’s Guide