hash32 man page on FreeBSD

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

     hash, hash32, hash32_buf, hash32_str, hash32_strn, hash32_stre,
     hash32_strne — general kernel hashing functions

     #include <sys/hash.h>

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

     hash32_str(const void *buf, uint32_t hash);

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

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

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

     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

     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

     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 charac‐
     ter 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.

     The hash32() functions return a 32 bit hash value of the buffer or

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


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

	   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;

     free(9), hashinit(9), malloc(9)

     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.

     The hash functions were first committed to NetBSD 1.6.  The OpenBSD ver‐
     sions were written and massaged for OpenBSD 2.3 by Tobias Weingartner,
     and finally committed for OpenBSD 3.2.

BSD				 April 3, 2007				   BSD

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