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spooky_hash128.3
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spooky_hash128.3
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.\" ========================================================================
.\"
.IX Title "spooky_hash128 3"
.TH spooky_hash128 3 "2015-03-30" "" ""
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
spooky_hash128 \- generate a "spooky" hash of an arbitrary blob of data
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
#include <spooky\-c.h>
.PP
void spooky_hash128(const void *message, size_t len, uint64_t *hash1, uint64_t *hash2);
.PP
uint64_t spooky_hash64(const void *message, size_t len, uint64_t seed);
.PP
uint32_t spooky_hash32(const void *message, size_t len, uint32_t seed);
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Quoting from Bob Jenkins' web page (inventor of the spooky hash
function):
.PP
\&\*(L"SpookyHash is a public domain noncryptographic hash function producing
well-distributed 128\-bit hash values for byte arrays of any length.\*(R"
.PP
It can also produce 64\-bit and 32\-bit hash values too, by simply
discarding the upper bits of the returned hash value. \fBspooky_hash32\fR
and \fBspooky_hash64\fR are wrappers around \fBspooky_hash128\fR that do
this discarding.
.PP
The \fBmessage\fR is a pointer to the stream of bytes to be hashed. \fBlen\fR
is the length of \fBmessage\fR. \fBseed\fR allows the function to generate
different hashes for the same key.
.PP
\&\fBspooky_hash128\fR also accepts seed values in \fBhash1\fR and \fBhash2\fR. Those
values will be overwritten with the actual hash results on return.
.SH "RETURN VALUE"
.IX Header "RETURN VALUE"
\&\fBspooky_hash64\fR and \fBspooky_hash32\fR return the hash value directly.
\&\fBspooky_hash128\fR is a void return function. It overwrites the two 64\-bit
integers that \fBhash1\fR and \fBhash2\fR on return. These functions never return
errors, only hash values.
.SH "NOTES"
.IX Header "NOTES"
The original code was written in \*(C+. The spooky-c library is a
reimplementation of the hash function in C. It's quite fast on 64\-bit
hardware.
.PP
There are some caveats with the SpookyHash function:
.IP "\(bu" 4
It was written for little-endian machines. It will run and work on
big-endian machines as well, but it will produce different results. Do
not use these functions if you plan to distribute these hashes in a
mixed endianness environment.
.IP "\(bu" 4
It is optimized for 64\-bit machines that can do unaligned reads.
It will work on 32\-bit hardware and on machines that require aligned
reads, but it won't perform as well on that hardware. You may want to
consider a different hash function in that situation.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Bob Jenkins' webpage on SpookyHash: <http://www.burtleburtle.net/bob/hash/spooky.html>
.SH "AUTHORS"
.IX Header "AUTHORS"
Bob Jenkins <[email protected]> invented the SpookyHash
algorithm and wrote the original \*(C+ implementation. The C implementation
(spooky-c) was written by Andi Kleen <[email protected]>. This
manpage was authored by Jeff Layton <[email protected]>.