HP-UX Floating-Point Guide

Chapter 4 101

HP-UX Math Libraries on HP 9000 Systems

Math Library Basics

Math libraries in most computer systems, including HP-UX, are

collections of frequently used mathematical functions. The functions

take one or more arguments and return one or more results. When an

application source ﬁle contains a use of a math function, the compiler

automatically generates a call to the appropriate routine name in the

appropriate math library. For example, suppose your Fortran program

contains the following declaration and statement:

DOUBLE PRECISION A, B, Y

Y = A**B

The statement raises A to the power B and assigns the result to Y. The

Fortran compiler emits a call to FTN_DTOD, which is one of the functions

in libcl.a and libcl.sl. libcl is the Fortran and Pascal library.

Conceptually, the deﬁnition of a math library function is simple; in this

example, FTN_DTOD merely raises a DOUBLE PRECISION value to the

power of another DOUBLE PRECISION value. However, there are

practical questions about math library functions that the programmer

may need to consider:

1. How accurate is the result returned?

2. How efﬁcient is the function (that is, how fast does it run)?

3. What happens when an error occurs (for example, overﬂow or invalid

arguments)?

4. What are the calling conventions for the function?

5. What functions are available?

The answers to questions 1 and 2 are implementation-dependent. The

answers to questions 3, 4, and 5 are determined by a variety of

programming environment speciﬁcations, such as XPG4.2.

Appendix A partially answers question 5 by listing the functions in the

HP-UX C math library. The Fortran equivalents are the intrinsic

functions; see the HP Fortran 90 Programmer’s Reference or the HP

FORTRAN/9000 Programmer’s Reference for a list of these functions.