libs/libc/search/hash_func.c

/****************************************************************************
 * libs/libc/search/hash_func.c
 *
 * SPDX-License-Identifier: BSD-3-Clause-UC
 * SPDX-FileCopyrightText: 1990, 1993 The Regents of the University of California.
 *
 * This code is derived from software contributed to Berkeley by
 * Margo Seltzer.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <sys/types.h>

#include <stdint.h>

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/

#define HASH4 h = (h << 5) + h + *key++;

/****************************************************************************
 * Private Types
 ****************************************************************************/

static uint32_t hash4(FAR const void *, size_t);

/****************************************************************************
 * Public Data
 ****************************************************************************/

/* Global default hash function */

uint32_t (*g_default_hash)(FAR const void *, size_t) = hash4;

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/* Hash function from Chris Torek. */

static uint32_t hash4(FAR const void *keyarg, size_t len)
{
  FAR const u_char *key = keyarg;
  uint32_t h = 0;
  size_t loop;

  if (len > 0)
    {
      loop = (len + 8 - 1) >> 3;
      switch (len & (8 - 1))
        {
          case 0:
            do
              {
                HASH4;

                /* FALLTHROUGH */

          case 7:
                HASH4;

                /* FALLTHROUGH */

          case 6:
                HASH4;

                /* FALLTHROUGH */

          case 5:
                HASH4;

                /* FALLTHROUGH */

          case 4:
                HASH4;

                /* FALLTHROUGH */

          case 3:
                HASH4;

                /* FALLTHROUGH */

          case 2:
                HASH4;

                /* FALLTHROUGH */

          case 1:
                HASH4;
              }
            while (--loop);
        }
    }

  return h;
}