A comparison of space requirements for short-circuit and full evaluation of Boolean expressions

Abstract

Short-circuit evaluation, instead of full evaluation, of Boolean expressions is a technique used in programming languages to save execution time and prevent run-time errors. In addition, use of short-circuiting may save space for the object code needed to evaluate Boolean expressions. In this article we show that whether shortcircuit or full evaluation requires less space depends on the processor architecture, the type of expression, and the compiler. After examining the types of Boolean expressions commonly used in programs, we give the minimal instruction sequences needed for their evaluation on a CISC architecture, a stack architecture, and a RISC architecture. We show that for commonly used architectures and Boolean expressions, short-circuit evaluation often requires less space for object code than full evaluation.