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hashfn.cpp
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1 /**********************************************************************
2 * File: hashfn.c (Formerly hash.c)
3 * Description: Simple hash function.
4 * Author: Ray Smith
5 * Created: Thu Jan 16 11:47:59 GMT 1992
6 *
7 * (C) Copyright 1992, Hewlett-Packard Ltd.
8 ** Licensed under the Apache License, Version 2.0 (the "License");
9 ** you may not use this file except in compliance with the License.
10 ** You may obtain a copy of the License at
11 ** http://www.apache.org/licenses/LICENSE-2.0
12 ** Unless required by applicable law or agreed to in writing, software
13 ** distributed under the License is distributed on an "AS IS" BASIS,
14 ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15 ** See the License for the specific language governing permissions and
16 ** limitations under the License.
17 *
18 **********************************************************************/
19
20 #include "mfcpch.h" //precompiled headers
21 #include "hashfn.h"
22
23 /**********************************************************************
24 * hash
25 *
26 * Simple hash function working on power of 2 table sizes.
27 * Uses xor function. Needs linear rehash.
28 **********************************************************************/
29
30 inT32 hash( //hash function
31 inT32 bits, //bits in hash function
32 void *key, //key to hash
33 inT32 keysize //size of key
34 ) {
35 inT32 bitindex; //current bit count
36 uinT32 keybits; //bit buffer
37 uinT32 hcode; //current hash code
38 uinT32 mask; //bit mask
39
40 mask = (1 << bits) - 1;
41 keysize *= 8; //in bits
42 bitindex = 0;
43 keybits = 0;
44 hcode = 0;
45 do {
46 while (keysize > 0 && bitindex <= 24) {
47 keybits |= *((uinT8 *) key) << bitindex;
48 key = (uinT8 *) key + 1;
49 bitindex += 8;
50 keysize -= 8;
51 }
52 hcode ^= keybits & mask; //key new key
53 keybits >>= bits;
54 }
55 while (keysize > 0);
56 return hcode; //initial hash
57 }