Also, it will fail when you add or remove null bytes.Ĭalculating a Cyclic Redundancy Check is a much more robust error checking algorithm. It will, however, fail badly when the message is modified by inverting or swapping groups of bytes. This system will detect many types of corruption with a reasonable probability. Usually the sum is truncated to, say, 32 bits. Just add together all the bytes in the message and append (or store somewhere else) the sum. You might, for instance, calculate a checksum. (Of course, if two bits are flipped–a much rarer occurrence–this system will not detect it.)įor messages longer than one byte, you’d like to store more than one bit of redundant information. If any of the nine bits is flipped, the sum will be odd and the computer will halt with a memory error. When reading the byte, the computer counts the number of non-zero bits in the byte, plus the parity bit. If the number is even, it sets the ninth parity bit, otherwise it clears it. Every time the byte gets written, the computer counts the number of non-zero bits in it. Many computers use one parity bit per byte of memory. Whether it’s an Ethernet packet or a file under the control of your application, you can add a piece of redundant information to validate it. Error detection is important whenever there is a non-zero chance of your data getting corrupted.
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