Hacker’s Delight, Second Edition

Chapter 4. Arithmetic Bounds

4–1 Checking Bounds of Integers

By “bounds checking” we mean to verify that an integer x is within two bounds a and b—that is, that

a ≤ x ≤ b.

We first assume that all quantities are signed integers.

An important application is the checking of array indexes. For example, suppose a one-dimensional array A can be indexed by values from 1 to 10. Then, for a reference A(i), a compiler might generate code to check that

1 ≤ i ≤ 10

and to branch or trap if this is not the case. In this section we show that this check can be done with a single comparison, by performing the equivalent check [PL8]:

This is probably better code, ...