1  /* Implements hashing function for string with known length.
       2     Copyright (C) 1996-2023 Free Software Foundation, Inc.
       3     This file is part of the GNU C Library.
       4  
       5     The GNU C Library is free software; you can redistribute it and/or
       6     modify it under the terms of the GNU Lesser General Public
       7     License as published by the Free Software Foundation; either
       8     version 2.1 of the License, or (at your option) any later version.
       9  
      10     The GNU C Library is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      13     Lesser General Public License for more details.
      14  
      15     You should have received a copy of the GNU Lesser General Public
      16     License along with the GNU C Library; if not, see
      17     <https://www.gnu.org/licenses/>.  */
      18  
      19  #include <sys/types.h>
      20  
      21  /* We assume to have `size_t' value with at least 32 bits.  */
      22  #define HASHWORDBITS 32
      23  
      24  
      25  /* Defines the so called `hashpjw' function by P.J. Weinberger
      26     [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools,
      27     1986, 1987 Bell Telephone Laboratories, Inc.]  */
      28  static size_t hash_string (const char *__str_param, size_t __len);
      29  
      30  static inline size_t
      31  hash_string (const char *str_param, size_t len)
      32  {
      33    size_t hval, g;
      34    const char *end_str = str_param + len;
      35  
      36    /* Compute the hash value for the given string.  */
      37    hval = len;
      38    while (str_param != end_str)
      39      {
      40        hval <<= 4;
      41        hval += (size_t) *str_param++;
      42        g = hval & ((size_t) 0xf << (HASHWORDBITS - 4));
      43        if (g != 0)
      44  	{
      45  	  hval ^= g >> (HASHWORDBITS - 8);
      46  	  hval ^= g;
      47  	}
      48      }
      49    return hval;
      50  }