sdbm_hash.c

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/* Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
/*
 * sdbm - ndbm work-alike hashed database library
 * based on Per-Aake Larson's Dynamic Hashing algorithms. BIT 18 (1978).
 * author: [email protected]
 * status: ex-public domain. keep it that way.
 *
 * hashing routine
 */
 
#include "apr_sdbm.h"
#include "sdbm_private.h"
 
/*
 * polynomial conversion ignoring overflows
 * [this seems to work remarkably well, in fact better
 * then the ndbm hash function. Replace at your own risk]
 * use: 65599   nice.
 *      65587   even better. 
 */
long sdbm_hash(const char *str, int len)
{
    register unsigned long n = 0;
 
#define DUFF    /* go ahead and use the loop-unrolled version */
#ifdef DUFF
 
#define HASHC   n = *str++ + 65599 * n
 
    if (len > 0) {
        register int loop = (len + 8 - 1) >> 3;
 
        switch(len & (8 - 1)) {
        case 0: do {
            HASHC;  case 7: HASHC;
        case 6: HASHC;  case 5: HASHC;
        case 4: HASHC;  case 3: HASHC;
        case 2: HASHC;  case 1: HASHC;
            } while (--loop);
        }
 
    }
#else
    while (len--)
        n = *str++ + 65599 * n;
#endif
    return n;
}