2016-01-08 16:27:27 +00:00
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.\"-
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.\" Copyright (c) 2016 Dag-Erling Smørgrav
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. The name of the author may not be used to endorse or promote
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.\" products derived from this software without specific prior written
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.\" permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.Dd January 8, 2016
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.Dt CRYB_FLETCHER 3
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.Os
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.Sh NAME
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.Nm cryb_fletcher16_hash ,
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.Nm cryb_fletcher32_hash ,
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.Nm cryb_fletcher64_hash
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.Nd hash functions
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.Sh LIBRARY
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.Lb libcryb-hash
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.Sh SYNOPSIS
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2016-09-17 15:30:13 +00:00
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.In stddef.h
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.In stdint.h
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.In cryb/hash.h
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.Ft uint16_t
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.Fn fletcher16_hash "const void *data" "size_t len"
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.Ft uint32_t
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.Fn fletcher32_hash "const void *data" "size_t len"
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.Ft uint64_t
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.Fn fletcher64_hash "const void *data" "size_t len"
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.Sh DESCRIPTION
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The
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.Fn cryb_fletcher16_hash ,
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.Fn cryb_fletcher32_hash
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and
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.Fn cryb_fletcher64_hash
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function return a 16-bit, 32-bit or 64-bit checksum of the
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.Va len
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first bytes of the object pointed to by
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.Va data .
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.Pp
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Unlike the Pearson hash implemented by
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2016-09-17 15:30:13 +00:00
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.Fn cryb_pearson_hash
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2016-01-08 16:27:27 +00:00
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or cryptographic message digests such as the SHA family, these
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checksums are suitable for error detection.
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.Sh IMPLEMENTATION NOTES
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Fletcher's paper assumes that the length of the input is a multiple of
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the algorithm's word size (half the output size), and does not specify
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or suggest how to handle odd-length input.
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This implementation zero-pads the input up to the nearest multiple of
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the word size.
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If strict compatibility with other implementations is required, the
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caller should take care to either pad the input or truncate the
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.Va len
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argument before calling the checksum function.
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.Sh SEE ALSO
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.Xr cryb_hash 3
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2016-09-17 15:30:13 +00:00
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.Sh STANDARDS
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2016-01-08 16:27:27 +00:00
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.Rs
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.%A "Fletcher, John G."
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.%D "January 1982"
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.%T "An Arithmetic Checksum for Serial Transmissions"
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.%J "IEEE Transactions on Communications"
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.%V "30"
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.%N "1"
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.%P "247-252"
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.%O "doi:10.1109/tcom.1982.1095369"
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.Re
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.Sh AUTHORS
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The
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.Fn cryb_fletcher16 ,
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.Fn cryb_fletcher32
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and
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.Fn cryb_fletcher64
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functions and this manual page were written by
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.An Dag-Erling Sm\(/orgrav Aq Mt des@des.no .
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