cyclic redundancy check
(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. (1997-08-02) Style="border-width:thin; border-color:#333333; border-Style:daShed; padding:5px;" align="left">In addition Suitable contentS:
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