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Both the XL Fortran compiler and the operating system provide facilities for working with floating-point exception conditions. To get more detailed location information about where the exception occurred, use -traceback (Linux and Mac OS) or /traceback (Windows). Do not mix these different facilities within a single program. All Rights Reserved.

On IA-32 and Intel® EM64T systems with SSE and SSE2 code, there is no performance degradation and possibly even a performance gain due to the fact that the hardware handles the When -ftz is used in combination with an SSE-enabling option (for example, -xN) on IA-32 systems, the compiler will insert code in the main routine to set FTZ and DAZ. IEEE divide-by-zero condition (Divide by Zero Raised) res_dbyz = -big / zero write(6,100)"Div-by-zero: ", -big, " /", zero, " = ", res_dbyz ! and call fpsets.

inx = and(rshift(flgs, fp_inexact) , 1) ! If you want to install a SIGTRAP signal handler, use the -qsigtrap option. Compiling with the -f77 compatibility flag will enable the Fortran 77 convention of automatically calling ieee_retrospective at program termination. Then, inside your program, manipulate the fpstats array (defined in the include file /usr/include/fpdc.h) and call the fpsets subroutine to specify which exceptions should generate traps.

When compiling with the -U option, you must code the names of these procedures in all lowercase. Provide your own routine sighndlr to do what you want when an exception is encountered, e.g call routine tracebk for a trace. The disadvantages of this approach include the following: You have to change your source code. To further reduce performance impact, you can include the imprecise suboption of the -qflttrap option.

IEEE arithmetic allows you to make distinctions about what kind of wrong answers can be ignored, such as NaN or Inf. Using the appropriate computer arithmetic is another. The resulting report is helpful for overviewing your code's FPEs, but it is not a replacement for a full trace report obtainable by the above methods. set OVERFL abort and trace values in f90sigfpe.h common block !

See fpversion(1), the Fortran User's Guide, and the Numerical Computation Guide for details. 6.3.1 Flags and ieee_flags() The ieee_flags function is used to query and clear exception status flags. My CEO wants permanent access to every employee's emails. By forcing the computation to double precision, you compute the dot product with greater accuracy and do not suffer underflows: DOUBLE PRECISION sum DO i = 1, n sum = sum In the future, use nans instead (although spnans still works, for backward compatibility).

When compiling different routines in a program separately, you should use the same value of n in -fpen. C integer sig, code, sigcontext(5) print *, 'ieee exception' stop end Cray trapping FPEs via subroutine calls Caveat: Cray C90 and J90 series run Cray arithmetic, not IEEE binary floating-point arithmetic. Example: f90 -64 -mips4 job.f -l fpe -l fpe_ss ssrun -fpe a.out prof a.out.fpe.m1043136 a.out SGI trapping FPEs via subroutine calls Documentation /usr/include/f90sigfpe (text file) OS and compiler: IRIX 64 6.5, turn on handler call handle_sigfpes 1 (FPE_ON, FPE_EN_OVERFL, 0, FPE_ABORT_ON_ERROR,abort_overfl) !

divide-by-zero: Divide-by-zero is signaled when the divisor is zero and the dividend is a finite nonzero number. The nonstandard_arithmetic() subroutine replaces an earlier routine named abrupt_underflow(). The IEEE standard supports user handling of exceptions, rounding, and precision. The following files are supplied for the modules xlf_fp_util: File names File type Locations xlf_fp_util.mod module symbol file (32-bit) /usr/lpp/xlf/include_32_d10 /usr/lpp/xlf/include_32_d7 Note:The files in these directories are exact copies of one

Both variables are declared as real(8). If you are unable to locate the offending source code, you should use the dbx debugger. Each vendor discussed in this note provides the subroutine-call interface for trapping FPEs in Fortran, but each has its own implementation, so portability is lost. xlf95 -qflttrap=ov compute_pi.f # Check one type, but do not trap.

If your program generates many underflows (perhaps a sign of a problem with your algorithm), you may experience a performance loss. IEEE overflow condition (Overflow Raised) res_oflow = big * big write(6,100)"Overflow: ", big, " *", big, " = ", res_oflow ! However, by calling ieee_handler() you can be more selective as to which exceptions to look at. Open hemisphere is connected Is there any job that can't be automated?

But if you have many FPEs, weeding them out in this manner can be tedious. To duplicate the floating-point behavior on UNICOS, set TRAP_FPE as follows: setenv TRAP_FPE \ "UNDERFL=FLUSH_ZERO; OVERFL=ABORT,TRACE; DIVZERO=ABORT,TRACE; \ INVALID=ABORT,TRACE" f90 -64 -mips4 job.f -l fpe a.out SGI trapping FPEs via ssrun But underflow is not a problem since Cray arithmetic automatically cuts over to zero. Users normally do not trap or handle this type of FPE, in deference to the others.

Continue execution to completion execution completed, exit code is 0 (dbx) To be selective, the example introduces the #include, which required renaming the source file with a .F suffix and calling Example: A convergence test based on the smallest number supported by the hardware would look like: IF ( delta .LE. Intervals can be used to: Solve nonlinear problems Perform rigorous error analysis Detect sources of numerical instability By introducing intervals as an intrinsic data type to Fortran 95, all of the job.f program main implicit none integer i real*8 u,v external fhandler_ !