Error trapping for multiprocessor systems:
A primer
last update:
04/10/2003
There are seven conditions that can cause FPEs on an IBM server. All of these conditions concern floating-point operations except integer overflow; integer overflow is also traced as an FPE. This section defines the seven conditions and a trap-enable option.
One form of underflow exception is signaled by the creation of a tiny nonzero result between the minimum expressible exponent, which, because it is tiny, may cause some other exception later. The other form of underflow exception is signaled by an extraordinary loss of accuracy during the approximation of such tiny numbers by denormalized numbers.
The overflow exception is signaled when what would have been the magnitude of the rounded floating-point result -- were the exponent range unbounded -- is larger than the destination format's largest finite number.
The divide-by-zero exception is signaled on an implemented divide operation if the divisor is zero and the dividend is a finite nonzero number.
The invalid operand exception is signaled when one or both of the operands are invalid for an implemented operation. The result (if not trapped) is NaN for floating-point numbers and not defined for fixed-point numbers.
The inexact result exception is signaled when the rounded result of an operation is not exact or if it overflows without an overflow trap.
This option checks for FPEs only on subprogram entry and exit. It is useful in than it has a minimal performance impact on the code.
This is a required option if using .qsigtrap (SIGTRAP). This allows SIGTRAP to process SIGFPEs.
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