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.Dd January 8, 2016
.Dt CRYB_FLETCHER 3
.Os
.Sh NAME
.Nm cryb_fletcher16_hash ,
.Nm cryb_fletcher32_hash ,
.Nm cryb_fletcher64_hash
.Nd hash functions
.Sh LIBRARY
.Lb libcryb-hash
.Sh SYNOPSIS
.In stddef.h
.In stdint.h
.In cryb/hash.h
.Ft uint16_t
.Fn fletcher16_hash "const void *data" "size_t len"
.Ft uint32_t
.Fn fletcher32_hash "const void *data" "size_t len"
.Ft uint64_t
.Fn fletcher64_hash "const void *data" "size_t len"
.Sh DESCRIPTION
The
.Fn cryb_fletcher16_hash ,
.Fn cryb_fletcher32_hash
and
.Fn cryb_fletcher64_hash
function return a 16-bit, 32-bit or 64-bit checksum of the
.Va len
first bytes of the object pointed to by
.Va data .
.Pp
Unlike the Pearson hash implemented by
.Fn cryb_pearson_hash
or cryptographic message digests such as the SHA family, these
checksums are suitable for error detection.
.Sh IMPLEMENTATION NOTES
Fletcher's paper assumes that the length of the input is a multiple of
the algorithm's word size (half the output size), and does not specify
or suggest how to handle odd-length input.
This implementation zero-pads the input up to the nearest multiple of
the word size.
If strict compatibility with other implementations is required, the
caller should take care to either pad the input or truncate the
.Va len
argument before calling the checksum function.
.Sh SEE ALSO
.Xr cryb_hash 3
.Sh STANDARDS
.Rs
.%A "Fletcher, John G."
.%D "January 1982"
.%T "An Arithmetic Checksum for Serial Transmissions"
.%J "IEEE Transactions on Communications"
.%V "30"
.%N "1"
.%P "247-252"
.%O "doi:10.1109/tcom.1982.1095369"
.Re
.Sh AUTHORS
The
.Fn cryb_fletcher16 ,
.Fn cryb_fletcher32
and
.Fn cryb_fletcher64
functions and this manual page were written by
.An Dag-Erling Sm\(/orgrav Aq Mt des@des.no .