1.1 Overview

Developing software within the confines of high-level languages like Fortran and C greatly increases the portability and maintainability of your source code. Many high-level languages support mathematical function evaluation. DPML was developed to provide a common set of routines that support many of the common mathematical functions across a wide variety of operating systems, hardware architectures, and languages.

In most cases, the common mathematical functions behave the same way for all languages and platforms. Occasionally, however, high- level language definitions of the same mathematical function will differ for specific input values. For example, in Fortran, log(- 1.0) causes a program abort, while in C, log(-1.0) quietly returns a system-defined value.

This document uses the term exceptional arguments to refer to values in the following situations:

Values for which high-level languages disagree on the function behavior.
Values that are mathematically undefined or out of range.
Values for which the function would overflow or underflow.

See Section 1.3 for more detail on exceptional arguments.

To provide uniform quality of mathematical functions for all languages on your system, DPML traps exceptional arguments and invokes a system-specific routine called the DPML exception handler. The exception handler is designed to work in conjunction with high- level language compilers and run-time libraries (RTLs) to provide specific language semantics for exceptional arguments. This means that the user-visible behavior of a given function called from a given language is not necessarily determined by the routines in the DPML library but rather by a combination of several entities acting in concert.

Note: Digital strongly recommends that you limit your access to the DPML routines documented in this manual to the high-level language syntax of your choice, thereby guaranteeing the behavior of the routines across platforms. Because of the complex relationship between high-level languages and DPML routines, the behavior of direct calls to DPML routines may change from release to release.