Dynamic Expression Evaluator for Real Time Applications

A dynamic expression evaluator developed for on-line data analysis gives experimenters at LBL´s 88-Inch Cyclotron and SuperHILAC both flexibility and high throughput. It uses standard FORTRAN rules for expressions, including operator precedence, and allows built-in functions such as sine and cosine. Evaluation techniques utilizing a combination of FORTRAN and Assembly, and XPL (a dialect of PL/1) have been compared. An XPL evaluator was selected because of development time and evaluator speed and can evaluate expressions at approximately 50 usec per operand on a ModComp Classic 7870 with 20 usec overhead per expression.