HP-UX Floating-Point Guide

Chapter 2 59
Floating-Point Principles and the IEEE Standard for Binary Floating-Point Arithmetic
Exception Conditions
If an invalid operation condition occurs when invalid operation traps are
disabled, the system by default returns a quiet NaN as the result of the
operation. If traps are enabled, the system signals a floating-point
exception and, if a trap handler is provided, takes whatever action the
trap handler dictates.
Division by Zero Conditions
A division by zero condition occurs whenever the system attempts to
divide a nonzero, finite value by zero. More generally, this condition
occurs whenever an exact infinity is produced from finite operands. If
divide-by-zero traps are disabled, the result is infinity: positive infinity if
the two operands have the same sign, negative infinity if they have
different signs. If traps are enabled, the system signals a floating-point
exception and, if a trap handler is provided, takes whatever action the
trap handler dictates.