CRC(2)CRC(2)NAMEcrc - 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 ALSOsum(1)CRC(2)
