~mdw / mLib / blame
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| c4ccbbf9 MW |
1 | .\" -*-nroff-*- |
| 2 | .\" | |
| 3 | .\" Manual for CRC23 calculator | |
| 4 | .\" | |
| 5 | .\" (c) 1999--2001, 2003, 2005, 2009, 2024 Straylight/Edgeware | |
| 6 | .\" | |
| 7 | . | |
| 8 | .\"----- Licensing notice --------------------------------------------------- | |
| 9 | .\" | |
| 10 | .\" This file is part of the mLib utilities library. | |
| 11 | .\" | |
| 12 | .\" mLib is free software: you can redistribute it and/or modify it under | |
| 13 | .\" the terms of the GNU Library General Public License as published by | |
| 14 | .\" the Free Software Foundation; either version 2 of the License, or (at | |
| 15 | .\" your option) any later version. | |
| 16 | .\" | |
| 17 | .\" mLib is distributed in the hope that it will be useful, but WITHOUT | |
| 18 | .\" ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
| 19 | .\" FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public | |
| 20 | .\" License for more details. | |
| 21 | .\" | |
| 22 | .\" You should have received a copy of the GNU Library General Public | |
| 23 | .\" License along with mLib. If not, write to the Free Software | |
| 24 | .\" Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, | |
| 25 | .\" USA. | |
| 26 | . | |
| 27 | .\"-------------------------------------------------------------------------- | |
| 28 | .so ../defs.man \" @@@PRE@@@ | |
| 29 | . | |
| 30 | .\"-------------------------------------------------------------------------- | |
| 31 | .TH crc32 3mLib "8 May 1999" "Straylight/Edgeware" "mLib utilities library" | |
| 32 | .\" @crc32 | |
| 33 | . | |
| 34 | .\"-------------------------------------------------------------------------- | |
| 35 | .SH NAME | |
| 36 | crc32 \- calculate 32-bit CRC | |
| 37 | . | |
| 38 | .\"-------------------------------------------------------------------------- | |
| 39 | .SH SYNOPSIS | |
| 40 | . | |
| 41 | .nf | |
| 42 | .B "#include <mLib/crc32.h>" | |
| 43 | .PP | |
| 44 | .BI "uint32 crc32(uint32 " crc ", const void *" buf ", size_t " sz ); | |
| 45 | .BI CRC32( result ", " crc ", " buf ", " sz ) | |
| 46 | .fi | |
| 47 | . | |
| 48 | .\"-------------------------------------------------------------------------- | |
| 49 | .SH DESCRIPTION | |
| 50 | . | |
| 51 | The | |
| 52 | .B crc32 | |
| 53 | function calculates a 32-bit cyclic redundancy check of the data block | |
| 54 | at address | |
| 55 | .I buf | |
| 56 | and size | |
| 57 | .I sz | |
| 58 | passed to it. | |
| 59 | .PP | |
| 60 | The function is restartable. For a first call, pass zero as the value | |
| 61 | of the | |
| 62 | .I crc | |
| 63 | argument; for subsequent blocks, pass in the previous output. The final | |
| 64 | answer is equal to the result you'd get from computing a CRC over the | |
| 65 | concatenation of the individual blocks. | |
| 66 | .PP | |
| 67 | The | |
| 68 | .B CRC32 | |
| 69 | macro calculates a CRC inline. The calculated CRC value is placed in | |
| 70 | the variable named by | |
| 71 | .IR result . | |
| 72 | Only use the macro version when efficiency is a major concern: it makes | |
| 73 | the code rather harder to read. | |
| 74 | .PP | |
| 75 | Note that a CRC is not cryptographically strong: it's fairly easy for an | |
| 76 | adversary to construct blocks of data with any desired CRC, or to modify | |
| 77 | a given block in a way which doesn't change its (unknown) CRC. | |
| 78 | .PP | |
| 79 | The exact behaviour of the CRC is beyond the scope of this manual; | |
| 80 | suffice to say that the result is, in some suitable representation, the | |
| 81 | remainder after division by a degree-32 polynomial in GF(2)[x]. | |
| 82 | . | |
| 83 | .\"-------------------------------------------------------------------------- | |
| 84 | .SH "RETURN VALUE" | |
| 85 | The return value is the 32-bit CRC of the input block. | |
| 86 | . | |
| 87 | .\"-------------------------------------------------------------------------- | |
| 88 | .SH "SEE ALSO" | |
| 89 | . | |
| 90 | .BR unihash (3), | |
| 91 | .BR mLib (3). | |
| 92 | . | |
| 93 | .\"-------------------------------------------------------------------------- | |
| 94 | .SH AUTHOR | |
| 95 | . | |
| 96 | Mark Wooding, <mdw@distorted.org.uk> | |
| 97 | . | |
| 98 | .\"----- That's all, folks -------------------------------------------------- |