Inside Macintosh: PowerPC Numerics / Part 1 - The PowerPC Numerics Environment

Chapter 3 - Expression Evaluation

About Expression Evaluation

The evaluation format of a floating-point operation is the data format used to evaluate the operation. An expression evaluation method is the means by which evaluation formats are determined. The IEEE standard does not cover expression evaluation methods, but the FPCE technical report does. Expression evaluation methods in PowerPC Numerics comply with the FPCE recommendations.

All PowerPC Numerics expression evaluation methods have a predefined minimum evaluation format, and they may or may not have widest-need evaluation. The minimum evaluation format is the narrowest evaluation format allowed for any operation. Any of the three floating-point data formats (single, double, or double-double) can be designated as the minimum evaluation format. Widest-need evaluation is a method used to determine the evaluation format for complex expressions (expressions with more than one floating-point operation). The following sections describe how expressions are evaluated without widest-need evaluation and with widest-need evaluation.