ref: 948870cffe2572efb68ef0b3873b36238fb53263
dir: /man/2/crc/
.TH CRC 2
.SH NAME
crc \- Crc module
.SH SYNOPSIS
.EX
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);
.EE
.SH DESCRIPTION
.B Crc
provides the routines to calculate the CRC (cyclic redundancy
check) over blocks of data.
.PP
.B Init
initializes the module and must be called first. The parameter
.I 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
.I 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.
.PP
.B Crc
calculates the CRC value of the first
.I nb
bytes of the array
.I buf
given the CRC state
.I state
as returned by the
.I 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.
.PP
.B Reset
sets the CRC state to its initial value in readiness for a new CRC
calculation. It avoids the need to call
.I init
again.
.SH SOURCE
.B /appl/lib/crc.b
.SH SEE ALSO
.IR sum (1)