NAME

crc − Crc module

SYNOPSIS

include "crc.m";
crc := load Crc Crc->PATH;
 CRCstate: adt {
crc: int;
crctab: array of int;
reg: int;
};
 init: fn(poly: int, reg: int): ref CRCstate;
crc: fn(state: ref CRCstate, buf: array of byte, nb: int): int;
reset: fn(state: ref CRCstate);

DESCRIPTION

­Crc provides the routines to calculate the CRC (cyclic redundancy check) over blocks of data. 

­Init initializes the module and must be called first. The parameter ­poly is the polynomial to use when calculating the CRC value. If a value of 0 is given, the default polynomial 16redb88320 (8r035556101440) is used. The polynomial has its implicit top bit set. The second parameter ­reg is the number with which to initialize the CRC register. This is commonly 0 but, for example, is 16rffffffff in the CRC32 algorithm. The final CRC value is also XORed with this number.  The function returns a pointer to an adt that holds the current CRC value, the auxiliary table the algorithm uses and the initial register value. These fields should not be accessed directly - they are only for internal use. 

­Crc calculates the CRC value of the first ­nb bytes of the array ­buf given the CRC state ­state as returned by the ­init function. It returns the current CRC value. It may be called repeatedly to calculate the CRC of a series of arrays of bytes, for example, when calculating the CRC value for the bytes in a file. 

­Reset sets the CRC state to its initial value in readiness for a new CRC calculation. It avoids the need to call ­init again. 

SOURCE

­/appl/lib/crc.b

SEE ALSO

sum(1)
 
 
 

Plan 9  —  June 29, 2000