[mLib] / man / crc32.3

.\" -*-nroff-*-
.TH crc32 3 "8 May 1999" "mLib"
.SH NAME
crc32 \- calculate 32-bit CRC
.\" @crc32
.SH SYNOPSIS
.nf
.B "#include <mLib/crc32.h>"

.BI "int crc32(unsigned long " crc ", const void *" buf ", size_t " sz );
.BI CRC32( result ", " crc ", " buf ", " sz )
.fi
.SH DESCRIPTION
The
.B crc32
function calculates a 32-bit cyclic redundancy check of the data block
at address
.I buf
and size
.I sz
passed to it.
.PP
The function is restartable.  For a first call, pass zero as the value
of the
.I crc
argument; for subsequent blocks, pass in the previous output.  The final
answer is equal to the result you'd get from computing a CRC over the
concatenation of the individual blocks.
.PP
The
.B CRC32
macro calculates a CRC inline.  The calculated CRC value is placed in
the variable named by
.IR result .
Only use the macro version when efficiency is a major concern: it makes
the code rather harder to read.
.PP
Note that a CRC is not cryptographically strong: it's fairly easy for an
adversary to construct blocks of data with any desired CRC, or to modify
a given block in a way which doesn't change its (unknown) CRC.
.PP
The exact behaviour of the CRC is beyond the scope of this manual;
suffice to say that the result is, in some suitable representation, the
remainder after division in the finite field GF(2^32) of the block by a
carefully chosen polynomial of order 32.
.SH "RETURN VALUE"
The return value is the 32-bit CRC of the input block.
.SH "SEE ALSO"
.BR mLib (3).
.SH AUTHOR
Mark Wooding, <mdw@nsict.org>
Commit	Line	Data
b6b9d458	1	.\" --nroff--
08da152e	2	.TH crc32 3 "8 May 1999" "mLib"
b6b9d458	3	.SH NAME
b6b9d458	4	crc32 \- calculate 32-bit CRC
08da152e	5	.\" @crc32
b6b9d458	6	.SH SYNOPSIS
	7	.nf
	8	.B "#include <mLib/crc32.h>"
	9
	10	.BI "int crc32(unsigned long " crc ", const void *" buf ", size_t " sz );
	11	.BI CRC32( result ", " crc ", " buf ", " sz )
	12	.fi
	13	.SH DESCRIPTION
	14	The
	15	.B crc32
	16	function calculates a 32-bit cyclic redundancy check of the data block
	17	at address
	18	.I buf
	19	and size
	20	.I sz
	21	passed to it.
	22	.PP
	23	The function is restartable. For a first call, pass zero as the value
	24	of the
	25	.I crc
	26	argument; for subsequent blocks, pass in the previous output. The final
	27	answer is equal to the result you'd get from computing a CRC over the
	28	concatenation of the individual blocks.
	29	.PP
	30	The
	31	.B CRC32
	32	macro calculates a CRC inline. The calculated CRC value is placed in
	33	the variable named by
	34	.IR result .
	35	Only use the macro version when efficiency is a major concern: it makes
	36	the code rather harder to read.
	37	.PP
	38	Note that a CRC is not cryptographically strong: it's fairly easy for an
	39	adversary to construct blocks of data with any desired CRC, or to modify
	40	a given block in a way which doesn't change its (unknown) CRC.
	41	.PP
	42	The exact behaviour of the CRC is beyond the scope of this manual;
	43	suffice to say that the result is, in some suitable representation, the
	44	remainder after division in the finite field GF(2^32) of the block by a
	45	carefully chosen polynomial of order 32.
	46	.SH "RETURN VALUE"
	47	The return value is the 32-bit CRC of the input block.
08da152e	48	.SH "SEE ALSO"
08da152e	49	.BR mLib (3).
b6b9d458	50	.SH AUTHOR
b6b9d458	51	Mark Wooding, <mdw@nsict.org>