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 Copyright (c) 2001 The NetBSD Foundation, Inc.
 All rights reserved.

 This code is derived from software contributed to The NetBSD Foundation
 by Luke Mewburn of Wasabi Systems, Inc.

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.Dd December 5, 2001
.Dt HASH 9
.Os
.Sh NAME
.Nm hash ,
.Nm hash32_buf ,
.Nm hash32_str ,
.Nm hash32_strn
.Nd kernel hash functions
.Sh SYNOPSIS
n sys/types.h n sys/hash.h .Ft uint32_t
.Fn hash32_buf "const void *buf" "size_t len" "uint32_t ihash"
.Ft uint32_t
.Fn hash32_str "const void *buf" "uint32_t ihash"
.Ft uint32_t
.Fn hash32_strn "const void *buf" "size_t len" "uint32_t ihash"
.Sh DESCRIPTION
The
.Nm
functions returns a hash of the given buffer.

p
The
.Fn hash32_buf
function returns a 32 bit hash of
.Fa buf ,
which is
.Fa len
bytes long,
seeded with an initial hash of
.Fa ihash
(which is usually
.Dv HASH32_BUF_INIT ) .
This function may use a different algorithm to
.Fn hash32_str
and
.Fn hash32_strn .

p
The
.Fn hash32_str
function returns a 32 bit hash of
.Fa buf ,
which is
a
.Dv NUL
terminated
.Tn ASCII
string,
seeded with an initial hash of
.Fa ihash
(which is usually
.Dv HASH32_STR_INIT ) .
This function must use the same algorithm as
.Fn hash32_strn ,
so that the same data returns the same hash.

p
The
.Fn hash32_strn
function returns a 32 bit hash of
.Fa buf ,
which is
a
.Dv NUL
terminated
.Tn ASCII
string,
up to a maximum of
.Fa len
bytes,
seeded with an initial hash of
.Fa ihash
(which is usually
.Dv HASH32_STR_INIT ) .
This function must use the same algorithm as
.Fn hash32_str ,
so that the same data returns the same hash.

p
The
.Fa ihash
parameter is provided to allow for incremental hashing by allowing
successive calls to use a previous hash value.
.Sh RETURN VALUES
The
.Fa hash32_*
functions return a 32 bit hash of the provided buffer.
.Sh HISTORY
The kernel hashing API first appeared in
.Nx 1.6 .