hash32_buf(9) [netbsd man page]

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

NAME

     hash, hash32_buf, hash32_str, hash32_strn -- kernel hash functions

SYNOPSIS

     #include <sys/types.h>
     #include <sys/hash.h>

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

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

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

DESCRIPTION

     The hash functions returns a hash of the given buffer.

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

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

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

     The ihash parameter is provided to allow for incremental hashing by allowing successive calls to use a previous hash value.

RETURN VALUES

     The hash32_* functions return a 32 bit hash of the provided buffer.

HISTORY

     The kernel hashing API first appeared in NetBSD 1.6.

BSD
								 December 5, 2001							       BSD

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

NAME

     hash, hash32, hash32_buf, hash32_str, hash32_strn, hash32_stre, hash32_strne -- 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);

DESCRIPTION

     The hash32() functions are used to give a consistent and general interface 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.

     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.  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
     additional 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 terminated hashing.

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 values 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 were first committed to NetBSD 1.6.  The OpenBSD versions were written and massaged for OpenBSD 2.3 by Tobias Weingartner,
     and finally committed for OpenBSD 3.2.

BSD
								   April 3, 2007							       BSD