HP-UX Floating-Point Guide

154 Chapter 6

Floating-Point Trap Handling

Enabling Traps

If you compile this program with traps disabled (the default), it produces

the following output:

1.7900+308 divided by 2.2000-308 = +INF

If you compile it with the +FP option, however, you get a core dump. (The

O ﬂag of the +FP option enables traps for overﬂow exceptions.)

$ f90 +FPO overflow.f

overflow.f

program OVERFLOW

11 Lines Compiled

$ ./a.out

Floating exception (core dumped)

Using the fesettrapenable Function

The fesettrapenable function is part of the fenv(5) suite and is

described in detail in “Exception Bits” on page 132. It is provided in the

C math library.

The fesettrapenable routine can enable one or more traps in any

combination.

Using fesettrapenable to enable traps has the same disadvantages as

the +FP option. You get a core dump, and you cannot determine the

exception type.

NOTE Do not use this function at an optimization level greater than 0. See

“Run-Time Mode Control: The fenv(5) Suite” on page 127. (You may

instead use the FLOAT_TRAPS_ON pragma to suppress optimization.)

Here is the program from “Using the +FP Compiler Option” on page 153,

modiﬁed to enable a trap for the overﬂow exception using

fesettrapenable. It does this by using an !$HP$ ALIAS or $ALIAS

directive to tell the Fortran compiler that the function’s arguments are

passed by value.