BREXX/370 User’s Guide

Indices and tables

This user’s guide documents the BREXX standard functions from https://ftp.gwdg.de/pub/languages/rexx/brexx/html/rx.html as well as the changes and amendments to BREXX to be used on MVS 3.8j.

Credits

  • BREXX has been developed by Vasilis Vlachoudis, who made it publicly available as freeware for non-commercial purposes.

  • Jason Winter’s JCC Compiler for compiled BREXX

  • JCC and the JCC-Library are owned and maintained by him. While not being freeware, Jason allows non-commercial usage and distribution of Software created using JCC through a relaxed license, as long as the complete source code always accompanies those distributions.

  • Vasilis and Jason explicitly consented to make the JCC based version of BREXX available on TK4-. Thanks to both for their significant valuable contribution to the TK4- MVS 3.8j Tur(n)key system.

  • The VSAM Interface is based on Steve Scott’s VSAM API.

  • The FSS Part is based on Tommy sprinkle’s FSS - TSO Full-Screen Services

  • Daniel Gaeta contributed his EXECIO implementation.

  • The NJE38DIR load module was extracted out of Bob Polmanter’s NJE38 V2 modules

We wish to thank the following persons for patiently answering our questions and for their support and advice:

  • Vasilis Vlachoudis

  • Jürgen Winkelmann

  • Jason Winter

  • Wally Mclaughlin

  • Greg Price

  • Bob Polmanter

  • Steve Scott

and many others!

BREXX/370 Source Code

The BREXX/370 Source Code can be found and downloaded at: https://github.com/mvslovers/brexx370/

Some Notes on BREXX Arithmetic Operations

BREXX stores numeric values in the appropriate type format. The benefit compared to save it as strings is a significant performance improvement during calculations. As the expensive string to numeric conversion before and vice versa after arithmetic operations is omitted; this allows speedy calculations without the required conversion overhead.

BREXX supports two numeric types:

  • Integer Integers are stored in 4-bytes a full word (LONG), this means their range is from -2,147,483,648 to +2,147,483,647

  • Decimal Numbers Decimal Numbers (decimal numbers with a fractional part) are represented in the double-precision floating-point format (doubleword), the length is 8-bytes consisting of an exponent and the significand (fraction). It consists of 56 bits for the fraction part, 7-bit exponent and one-bit for the sign. This representation is IBM specific and differs slightly from the IIEE 754 floating-point standard.

    The precision of floating-point numbers is not as good as decimal packed numbers which are not supported in BREXX (nor in REXX). This means, for example, 2.0 might be stored as 19999999999999999e-17, or for 5.0 you will is stored as 50000000000000003e-17; this is not an error, but the usual behaviour for floating-point numbers. It is caused by the conversion between the numbers of base 10 to base two a bit-exact reversibility is not always given. This effect may build up during arithmetic calculations.