CRC(2) CRC(2)
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)
CRC(2) CRC(2)