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    Length: 2380 (0x94c)
    Types: TextFile
    Names: »hash.c«

└─⟦a05ed705a⟧ Bits:30007078 DKUUG GNU 2/12/89
    └─⟦0befd2614⟧ »./gdbm-0.8.tar.Z« 
        └─⟦b993d2893⟧ 
            └─⟦this⟧ »gdbm/hash.c« 

TextFile

/* hash.c - The dbm hash function. */

/*  GNU DBM  - DataBase Manager (database subroutines) by Philip A. Nelson
    Copyright (C) 1989  Free Software Foundation, Inc.

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

    You may contact the author by:
       e-mail:  phil@wwu.edu
      us-mail:  Philip A. Nelson
                Computer Science Department
                Western Washington University
                Bellingham, WA 98226
        phone:  (206) 676-3035
       
*************************************************************************/



#include <stdio.h>
#include <sys/file.h>
#include <sys/types.h>
#include <sys/stat.h>
#include "gdbm.h"

#ifdef RANDOM_HASH
#include "extern.h"
#endif /* RANDOM_HASH */


/* This hash function computes a 31 bit value.  The value is used to index
   the hash directory using the top n bits.  It is also used in a hash bucket
   to find the home position of the element by taking the value modulo the
   bucket hash table size. */

int
_dbm_hash (key)
     datum key;
{
  int  value;		/* Used to compute the hash value.  */
  char *old_state;	/* Remember the old random state.  */
  int  index;		/* Used to cycle through random values. */

#ifdef RANDOM_HASH
  /* Set the random number generator to our state. */
  old_state = (char *) setstate (_dbm_hash_state); 
#endif /* RANDOM_HASH */

  /* Set the initial value from key. */
  value = 0;
  for (index = 0; index < key.dsize; index++)
    value = (value + (key.dptr[index] << (index*5 % 24))) & 0x3FFFFFFF;

#ifdef RANDOM_HASH
  /* Produce the final value. */
  srandom(value);
  for (index = 0; index < key.dsize; index++)
    value = random();

  /* Restore the random number generator. */
  setstate (old_state); 
#endif /* RANDOM_HASH */

  /* Return the value. */
  return value;
}