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HASH(9)			 BSD Kernel Developer's	Manual		       HASH(9)

NAME
     hash, hash32, hash32_buf, hash32_str, hash32_strn,	hash32_stre,
     hash32_strne, jenkins_hash, jenkins_hash32, murmur3_32_hash,
     murmur3_32_hash32 -- general kernel hashing functions

SYNOPSIS
     #include <sys/hash.h>

     uint32_t
     hash32_buf(const void *buf, size_t	len, uint32_t hash);

     uint32_t
     hash32_str(const void *buf, uint32_t hash);

     uint32_t
     hash32_strn(const void *buf, size_t len, uint32_t hash);

     uint32_t
     hash32_stre(const void *buf, int end, const char **ep, uint32_t hash);

     uint32_t
     hash32_strne(const	void *buf, size_t len, int end,	const char **ep,
	 uint32_t hash);

     uint32_t
     jenkins_hash(const	void *buf, size_t len, uint32_t	hash);

     uint32_t
     jenkins_hash32(const uint32_t *buf, size_t	count, uint32_t	hash);

     uint32_t
     murmur3_32_hash(const void	*buf, size_t len, uint32_t hash);

     uint32_t
     murmur3_32_hash32(const uint32_t *buf, size_t count, uint32_t hash);

DESCRIPTION
     The hash32() functions are	used to	give a consistent and general inter-
     face to a decent hashing algorithm	within the kernel.  These functions
     can be used to hash ASCII NUL terminated strings, as well as blocks of
     memory.

     A len argument is the length of the buffer	in bytes.  A count argument is
     the length	of the buffer in 32-bit	words.

     The hash32_buf() function is used as a general buffer hashing function.
     The argument buf is used to pass in the location, and len is the length
     of	the buffer in bytes.  The argument hash	is used	to extend an existing
     hash, or is passed	the initial value HASHINIT to start a new hash.

     The hash32_str() function is used to hash a NUL terminated	string passed
     in	buf with initial hash value given in hash.

     The hash32_strn() function	is like	the hash32_str() function, except it
     also takes	a len argument,	which is the maximal length of the expected
     string.

     The hash32_stre() and hash32_strne() functions are	helper functions used
     by	the kernel to hash pathname components.	 These functions have the ad-
     ditional termination condition of terminating when	they find a character
     given by end in the string	to be hashed.  If the argument ep is not NULL,
     it	is set to the point in the buffer at which the hash function termi-
     nated hashing.

     The jenkins_hash()	function has same semantics as the hash32_buf(), but
     provides more advanced hashing algorithm with better distribution.

     The jenkins_hash32() uses same hashing algorithm as the jenkins_hash()
     function, but works only on uint32_t sized	arrays,	thus is	simpler	and
     faster.  It accepts an array of uint32_t values in	its first argument and
     size of this array	in the second argument.

     The murmur3_32_hash() and murmur3_32_hash32() functions are similar to
     jenkins_hash() and	jenkins_hash32(), but implement	the 32-bit version of
     MurmurHash3.

RETURN VALUES
     The hash32() functions return a 32	bit hash value of the buffer or
     string.

EXAMPLES
	   LIST_HEAD(head, cache) *hashtbl = NULL;
	   u_long mask = 0;

	   void
	   sample_init(void)
	   {

		   hashtbl = hashinit(numwanted, type, flags, &mask);
	   }

	   void
	   sample_use(char *str, int len)
	   {
		   uint32_t hash;

		   hash	= hash32_str(str, HASHINIT);
		   hash	= hash32_buf(&len, sizeof(len),	hash);
		   hashtbl[hash	& mask]	= len;
	   }

SEE ALSO
     free(9), hashinit(9), malloc(9)

LIMITATIONS
     The hash32() functions are	only 32	bit functions.	They will prove	to
     give poor 64 bit performance, especially for the top 32 bits.  At the
     current time, this	is not seen as a great limitation, as these hash val-
     ues are usually used to index into	an array.  Should these	hash values be
     used for other means, this	limitation should be revisited.

HISTORY
     The hash functions	first appeared in NetBSD 1.6.  The current implementa-
     tion of hash32 functions was first	committed to OpenBSD 3.2, and later
     imported to FreeBSD 6.1.  The jenkins_hash	functions were added in
     FreeBSD 10.0.  The	murmur3_32_hash	functions were added in	FreeBSD	10.1.

AUTHORS
     The hash32	functions were written by Tobias Weingartner.  The
     jenkins_hash functions were written by
     Bob Jenkins.  The murmur3_32_hash functions were written by
     Dag-Erling	Smorgrav <des@FreeBSD.org>.

BSD				 June 30, 2015				   BSD

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | EXAMPLES | SEE ALSO | LIMITATIONS | HISTORY | AUTHORS

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