Arithmetic Overflow Definition

An arithmetic overflow happens when, in a numerical calculation, a number is produced that is too large for the variable that is supposed to hold it and crazy or false behavior results.

The overflow usually takes place during integer operations or with fixed-size numeric types, when the resulting number goes beyond the highest or lowest limits of the variable. For instance, in case an 8-bit variable (which can hold values from 0 to 255) is assigned a value of 260, it either gets rolled back or truncated as per the system used.

The above is a typical case of wrapping whereby the numbers are said to “loop back” to the starting point of the range, just like counting on fingers after reaching the maximum and then starting over again.

Impact on Software

Arithmetic overflow leads to the following consequences:

• Incorrect calculations. The output can be far from the intended results.
• System errors or crashes. The flow of the program can become unpredictable if the overflow goes undetected.
• Security vulnerabilities. The attackers can use the overflow as a tool to enable the buffer overflow or to gain a foothold for deploying their malware.

Overflow Prevention

In most cases, software engineers come up with ways to prevent overflow from happening or to cope with it in case it occurs:

• Clamping. Some systems restrict values to be either the maximum or minimum allowable.
• Type selection. Choosing larger data types that can hold higher values.
• Error detection. Overflow is found and dealt with before it causes troubles.

In today’s software development, knowledge and management of arithmetic overflow are very important for getting the application to be reliable, safe, and predictable.