Rational Developer for System z
COBOL for Windows, Version 7.5, Programming Guide


Grouping constant computations

When several items in an expression are constant, ensure that the optimizer is able to optimize them. The compiler is bound by the left-to-right evaluation rules of COBOL. Therefore, either move all the constants to the left side of the expression or group them inside parentheses.

For example, if V1, V2, and V3 are variables and C1, C2, and C3 are constants, the expressions on the left below are preferable to the corresponding expressions on the right:

More efficient Less efficient
V1 * V2 * V3 * (C1 * C2 * C3) V1 * V2 * V3 * C1 * C2 * C3
C1 + C2 + C3 + V1 + V2 + V3 V1 + C1 + V2 + C2 + V3 + C3

In production programming, there is often a tendency to place constant factors on the right-hand side of expressions. However, such placement can result in less efficient code because optimization is lost.


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