AMD 250 manual Long Logical Expressions in If Statements

Software Optimization Guide for AMD64 Processors 25112 Rev. 3.06 September 2005

2.5Long Logical Expressions in If Statements

Optimization

In if statements, avoid long logical expressions that can generate dense conditional branches that violate the guideline described in “Density of Branches” on page 126.

Application

This optimization applies to:

•32-bit software

•64-bit software

Rationale

Listing 1. Preferred for Data that Falls Mostly Within the Range

if (a <= max && a >= min && b <= max && b >= min)

If most of the data falls within the range, the branches will not be taken, so the above code is preferred. Otherwise, the following code is preferred.

Listing 2. Preferred for Data that Does Not Fall Mostly Within the Range

if (a > max a < min b > max b < min)

16 C and C++ Source-Level Optimizations Chapter 2