![]() ![]() The number of zero bits added to the message is the same as the width of the checksum (what I call c) in this case four bits were added. The number to be divided is the message augmented with zeros at the end. We'll use the example in Figure 1 to guide us. So even if your processor has a division instruction, you won't be able to use it.īefore writing even one line of code, let's first examine the mechanics of modulo-2 binary division. For another, modulo-2 binary division is not the same as ordinary division. For one thing, generally no registers are available to hold the very long bit sequence that is the numerator. Modulo-2 binary division doesn't map particularly well to the instruction sets of off-the-shelf processors. Knowing that all CRC algorithms are simply long division algorithms in disguise doesn't help. However, I'm going to keep the discussion at the level of the C language further steps could be taken to improve the efficiency of the final code by moving into the assembly language of your particular processor.įor most software engineers, the overwhelmingly confusing thing about CRCs is their implementation. I'll start with a naive implementation and gradually improve the efficiency of the code as I go along. I'm going to complete my 3-part discussion of checksums by showing you how to implement a CRC in C. However, sometimes you must compute a CRC in software, for example in a C or C++ program that will run in an embedded system. Generally speaking, CRCs are most efficiently calculated in dedicated hardware. If you suspect data corruption has led to a system failure, Barr Group can help by performing forensic analysis and reverse engineering services. This article shows how to implement an efficient CRC in C or C++.ĭownload Barr Group's Free CRC Code in C now.Ī CRC is a powerful type of checksum that is able to detect corruption of data that is stored in and/or transmitted between computers. Unfortunately, the modulo-2 arithmetic used to compute CRCs doesn't map easily into software. Cyclic Redundancy Codes (CRCs) are among the best checksums available to detect and/or correct errors in communications transmissions. ![]()
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