HP-UX Floating-Point Guide

220 Appendix C

Floating-Point Problem Checklist

Results Different from Those Produced Previously

For information about the effects of compiler version changes, see

“Compiler Behavior and Compiler Version” on page 78.

• Are you using different compiler options? Compiling at a different

optimization level may change the way the compiler performs such

operations as expression reordering and operation reordering.

For more information, see “Compiler Options” on page 79 and

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

• Have you changed the rounding mode or the underﬂow mode for your

application? If you use the fesetround function to change the

rounding mode from the default (round to nearest), application

results will probably change. If you use the fesetflushtozero

function or the +FP compiler option to change the underﬂow mode to

ﬂush-to-zero mode, results that underﬂow are ﬂushed to 0 instead of

denormalized, and application results may also change.

For more information, see “Values of Certain Modiﬁable Hardware

Status Register Fields” on page 82 and all of Chapter 5.