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     hash, hash32, hash32_buf, hash32_str, hash32_strn, hash32_stre, hash32_strne,
     jenkins_hash32, jenkins_hash — 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);

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

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


     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

     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.

     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 simplier and faster.  It accepts an array of uint32_t
     values in its first argument and size of this array in the second argument.


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


           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 values 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 first appeared in NetBSD 1.6.  The current implementation 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 hash32 functions were written by Tobias Weingartner.  The jenkins_hash functions was
     written by Bob Jenkins .