HP-UX Floating-Point Guide

Appendix C 219
Floating-Point Problem Checklist
Results Different from Those Produced Previously
Results Different from Those Produced
Previously
If your application produces results that are somewhat different from
those produced when you ran it before (either on HP-UX or on another
vendor’s system), consider the following possibilities:
• Are you porting an application to HP-UX from another vendor’s
system? If the other system does not comply with the IEEE standard,
your results will almost certainly be different on HP-UX. If the other
system is also IEEE-compliant, slight differences in results may come
from differences in the rounding errors introduced by variations in
the ordering of basic operations within expressions or within library
functions.
See Chapter 2 for an overview of the IEEE standard. See “How Basic
Operations Affect Application Results” on page 71 for information on
how basic operations affect results.
• Did you use a different version of the math library? Different versions
of the HP-UX operating system will often contain improved versions
of the math libraries. Your application may be affected by these
changes if it uses shared libraries or if you have rebuilt it on a system
that is running a different version of HP-UX. Using the +DA option on
the compile command line also affects which library version you use.
For details, see “Math Libraries and System Architecture” on page 25,
“Operating System Release of Build-Time System” on page 81, and
“Operating System Release of Run-Time System” on page 81.
For more information about the effects of math library changes, see
“How Mathematical Library Functions Affect Application Results” on
page 73 and “Operating System Release of Build-Time System” on
page 81. For specific information about the enhanced HP-UX math
libraries, see “Contents of the HP-UX Math Libraries” on page 112,
Appendix A, and Appendix B.
• Are you using a different compiler, or a different version of the
compiler? A new compiler version may perform such operations as
constant parsing and constant folding somewhat differently. It may
also order some expressions somewhat differently.