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.\" $DragonFly: src/share/man/man9/hash.9,v 1.3 2004/07/16 05:04:36 hmp Exp $
.\"
.Dd May 14, 2004
.Os
.Dt HASH 9
.Sh NAME
.Nm hash ,
.Nm hashinit ,
.Nm phashinit
.Nd generic hash table functions for the kernel
.Sh SYNOPSIS
.In sys/param.h
.In sys/systm.h
.In sys/malloc.h
.Ft void *
.Fn hashinit "int elements" "struct malloc_type *type" "u_long *hashmask"
.Ft void *
.Fn phashinit "int elements" "struct malloc_type *type" "u_long *nentries"
.Sh DESCRIPTION
The kernel hash functions are used for creating a generic hash table.
.Pp
The
.Fn hashinit
function returns a pointer to a hash table which is sized a
.Dq "power of two"
greater or equal to the number of
.Fa elements
requested.
The masking value is stored in
.Fa hashmask .
.Pp
The
.Fn phashinit
function returns a pointer to a prime number sized hash table.
The number of
.Fa elements
requested is used to dictate an upper-bound for the size of the
hash table.
The final size of the hash table is stored by the function in
.Fa nentries .
.Pp
The
.Fa type
argument to both of the above functions is used for keeping track
of memory allocated for the hash table.
See the
.Xr malloc 9
manual page for more information on memory statistics.
.Sh CODE REFERENCES
The VFS namecache code is one of many examples for using the
.Fn hashinit
function; it is located within the file
.Pa sys/kern/vfs_cache.c .
.Pp
The hostcache code uses the
.Fn phashinit
function for creating a prime number sized hash table; it is located
within the file
.Pa sys/net/hostcache.c .
.Pp
All pathnames in this section are relative to the
.Dx
source tree.
.Sh SEE ALSO
.Xr tcp 4 ,
.Xr udp 4 ,
.Xr malloc 9 ,
.Xr namei 9
.Sh AUTHORS
This manual page was written by
.An Hiten Pandya Aq hmp@backplane.com .