@@@ much mess, mostly manpages

[mLib] / hash / crc32.3.in

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+.\" -*-nroff-*-
+.\"
+.\" Manual for CRC23 calculator
+.\"
+.\" (c) 1999--2001, 2003, 2005, 2009, 2024 Straylight/Edgeware
+.\"
+.
+.\"----- Licensing notice ---------------------------------------------------
+.\"
+.\" This file is part of the mLib utilities library.
+.\"
+.\" mLib is free software: you can redistribute it and/or modify it under
+.\" the terms of the GNU Library General Public License as published by
+.\" the Free Software Foundation; either version 2 of the License, or (at
+.\" your option) any later version.
+.\"
+.\" mLib is distributed in the hope that it will be useful, but WITHOUT
+.\" ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+.\" FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
+.\" License for more details.
+.\"
+.\" You should have received a copy of the GNU Library General Public
+.\" License along with mLib.  If not, write to the Free Software
+.\" Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
+.\" USA.
+.
+.\"--------------------------------------------------------------------------
+.so ../defs.man \" @@@PRE@@@
+.
+.\"--------------------------------------------------------------------------
+.TH crc32 3mLib "8 May 1999" "Straylight/Edgeware" "mLib utilities library"
+.\" @crc32
+.
+.\"--------------------------------------------------------------------------
+.SH NAME
+crc32 \- calculate 32-bit CRC
+.
+.\"--------------------------------------------------------------------------
+.SH SYNOPSIS
+.
+.nf
+.B "#include <mLib/crc32.h>"
+.PP
+.BI "uint32 crc32(uint32 " 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 by a degree-32 polynomial in GF(2)[x].
+.
+.\"--------------------------------------------------------------------------
+.SH "RETURN VALUE"
+The return value is the 32-bit CRC of the input block.
+.
+.\"--------------------------------------------------------------------------
+.SH "SEE ALSO"
+.
+.BR unihash (3),
+.BR mLib (3).
+.
+.\"--------------------------------------------------------------------------
+.SH AUTHOR
+.
+Mark Wooding, <mdw@distorted.org.uk>
+.
+.\"----- That's all, folks --------------------------------------------------