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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.