# cyclic redundancy check

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## cyclic redundancy check

[′sīk·lik ri′dən·dən·sē ‚chek]
(computer science)
A block check character in which each bit is calculated by adding the first bit of a specified byte to the second bit of the next byte, and so forth, spiraling through the block.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

## cyclic redundancy check

(algorithm)
(CRC or "cyclic redundancy code") A number derived from, and stored or transmitted with, a block of data in order to detect corruption. By recalculating the CRC and comparing it to the value originally transmitted, the receiver can detect some types of transmission errors.

A CRC is more complicated than a checksum. It is calculated using division either using shifts and exclusive ORs or table lookup (modulo 256 or 65536).

The CRC is "redundant" in that it adds no information. A single corrupted bit in the data will result in a one bit change in the calculated CRC but multiple corrupted bits may cancel each other out.

CRCs treat blocks of input bits as coefficient-sets for polynomials. E.g., binary 10100000 implies the polynomial: 1*x^7 + 0*x^6 + 1*x^5 + 0*x^4 + 0*x^3 + 0*x^2 + 0*x^1 + 0*x^0. This is the "message polynomial". A second polynomial, with constant coefficients, is called the "generator polynomial". This is divided into the message polynomial, giving a quotient and remainder. The coefficients of the remainder form the bits of the final CRC. So, an order-33 generator polynomial is necessary to generate a 32-bit CRC. The exact bit-set used for the generator polynomial will naturally affect the CRC that is computed.

Most CRC implementations seem to operate 8 bits at a time by building a table of 256 entries, representing all 256 possible 8-bit byte combinations, and determining the effect that each byte will have. CRCs are then computed using an input byte to select a 16- or 32-bit value from the table. This value is then used to update the CRC.

Ethernet packets have a 32-bit CRC. Many disk formats include a CRC at some level.
References in periodicals archive ?
Back then, the only organized activity on CRC awareness was the Colorectal Cancer Awareness program conducted every March by The Medical City Colorectal Clinic under the leadership of noted colorectal surgeon Dr.
But Cleveland Police and Crime Commissioner Barry Coppinger hit out at a move to replace the Durham Tees Valley CRC with a region-wide body.
Another study from Karachi, Pakistan also concluded that although CRC is usually a disease of older patients but it is increasingly becoming more common in younger population who present with more advanced disease and poorer prognosis.
Hereditary CRC has two forms, familial adenomatous polyposis (FAP) due to germline mutation in the gene APC (Soravia et al., 1998; Pedemonte et al., 1998; Sieber et al., 2002) and hereditiary nonpolyposis colorectal cancer (HNPCC), also called Lynch syndrome due to germline mutation in the DNA MMR genes (Nicolaides et al., 1994; Miyaki et al., 1997).
It's as simple as that," said former Attorney General Bob Butterworth, who served on the 1997-98 CRC.
Since 2005, Virginia has been using the CRC as the foundation for stackable credentials.
All CRC modules are certified by the National Maintenance Training Center at Camp Dodge, Iowa.
It further elaborates on the Adverse Event process and reporting, the differences in the classifications of Adverse Events and the necessary documentation needed from the CRC and Principal Investigator to ensure regulation compliance.
Many companies that would not have considered CRC services before now chose to store and manage inactive records with CRCs.
COMPUTATION OF CYCLIC REDUNDANCY CHECKS VIA TABLE LOOK-UP A Cyclic Redudancy Check (CRC) code provides a simple, yet powerful method for the detection of errors during digital data transmission.
CRC and other cancers in the breast, liver, lungs and kidneys are potentially curable if detected early enough and properly treated.

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