Fixed-point versus floating-point

In IBM® Enterprise COBOL Version 4 Release 2 Performance Tuning, it says: "When using fixed-point exponentiations with large exponents, the calculation can be done more efficiently by using operands that force the exponentiation to be evaluated in floating-point".

In V6, it is still true that floating point exponentiation is much faster than fixed-point exponentiation; however, the relative cost of each type of exponentiation has changed from V4 to V6.

Consider the following code example:

01 A PIC S9(6)V9(12) COMP-3 VALUE 0.
01 B PIC S9V9(12) COMP-3 VALUE 1.234567891.
01 C PIC S9(10) COMP-3 VALUE -9.

COMPUTE A = (1 + B) ** C. (original)
COMPUTE A = (1.0E0 + B) ** C. (forced to floating-point)

The original, fixed-point exponentiation, is 89% faster in V6 compared to V4.

The forced to floating point exponentiation is 39% faster in V6 compared to V4.

However, because floating point exponentiation remains many times faster than fixed-point exponentiation, it is still recommended to use floating point exponentiation whenever possible.