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hash (9)
  • hash (1) ( Solaris man: Команды и прикладные программы пользовательского уровня )
  • hash (1) ( FreeBSD man: Команды и прикладные программы пользовательского уровня )
  • hash (1) ( Linux man: Команды и прикладные программы пользовательского уровня )
  • hash (1) ( POSIX man: Команды и прикладные программы пользовательского уровня )
  • hash (3) ( FreeBSD man: Библиотечные вызовы )
  • hash (3) ( Русские man: Библиотечные вызовы )
  • hash (3) ( Linux man: Библиотечные вызовы )
  • >> hash (9) ( FreeBSD man: Ядро )
  • Ключ hash обнаружен в базе ключевых слов.

  • BSD mandoc
     

    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 Fa buf is used to pass in the location, and Fa len is the length of the buffer. The argument Fa 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 Fa buf with initial hash value given in Fa hash .

    The hash32_strn ();
    function is like the hash32_str ();
    function, except it also takes a Fa 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 Fa end in the string to be hashed. If the argument Fa 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 functions were first committed to Nx 1.6 . The Ox versions were written and massaged for Ox 2.3 by Tobias Weingartner, and finally committed for Ox 3.2 .


     

    Index

    NAME
    SYNOPSIS
    DESCRIPTION
    RETURN VALUES
    EXAMPLES
    SEE ALSO
    LIMITATIONS
    HISTORY


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