HP-UX Floating-Point Guide

Chapter 4 99

HP-UX Math Libraries on HP 9000 Systems

HP-UX Library Basics

A library is a collection of commonly used functions, precompiled in

object format and ready to be linked to an application. Because different

programming languages have different calling conventions, there are

separate libraries for various languages. On HP-UX systems, the C and

C++ languages use one set of libraries, while the Fortran and Pascal

languages use another.

In the HP-UX environment there are two types of libraries: archive

libraries and shared libraries.

An archive library is a collection of object modules. When an

application is linked with an archive library, the linker scans the

contents of the archive library and extracts the object modules that

satisfy any unresolved references in the application. The linker copies

the archive library modules into the application’s code section.

A shared library is also a collection of object modules. However, when

the linker scans a shared library, it does not copy modules into the

application’s code section. Instead, the linker preserves information in

the application’s code section about which unresolved references were

resolved in each shared library. At run time, the loader copies the

referenced modules from the shared library into memory. If multiple

applications linked with a common shared library execute

simultaneously, they will all share (or be attached to) the same physical

copy of the library in memory (hence the name shared library). The

shared library improves the efﬁciency of memory use and allows smaller

application binaries.

The name of an archive library is libname.a, and the name of a shared

library is libname.sl. Thus the library named m (for math) can have

versions named libm.a and libm.sl. The HP-UX system libraries are

in the directory /usr/lib.

By default, the HP-UX linker selects a shared version of a library, if one

is available. Although shared libraries save space in memory, using

shared libraries makes a program run more slowly. If your application

makes heavy use of math library functions, you may want to use archive

libraries instead of shared libraries. For more information about

performance issues related to shared and archive libraries, see “Shared

Libraries versus Archive Libraries” on page 181.