C251 User's Guide

Library Reference

The C251 run-time library provides more than 100 predefined functions and macros you may use in your 251 C programs. The library makes embedded software development easier by providing routines that perform common programming tasks such as string and buffer manipulation, data conversion, and floating-point math operations.

The routines in this library conform to the ANSI C Standard. However, some functions differ slightly in order to take advantage of the features of the 251 architecture. For example, the isdigit function returns a bit value as opposed to an int. Where possible, function return types and argument types are adjusted to use the smallest data type possible. In addition, unsigned data types are favored over signed types.

The floating pointer error handling is performed via the functions _chkfloat_ and _chkdouble_ rather then using a global variable errno for the error status. This method fits the needs of embedded systems, where the error status is checked separately in the main and interrupt function or in each RTX251 task.

These changes to the standard library provide a maximum of performance while reducing program size.

All routines in this library are implemented to be independent of and to function using any register bank.