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git-svn-id: https://tesseract-ocr.googlecode.com/svn/trunk@156 d0cd1f9f-072b-0410-8dd7-cf729c803f20
58 lines
2.0 KiB
C++
58 lines
2.0 KiB
C++
/**********************************************************************
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* File: hashfn.c (Formerly hash.c)
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* Description: Simple hash function.
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* Author: Ray Smith
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* Created: Thu Jan 16 11:47:59 GMT 1992
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*
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* (C) Copyright 1992, Hewlett-Packard Ltd.
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** Licensed under the Apache License, Version 2.0 (the "License");
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** you may not use this file except in compliance with the License.
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** You may obtain a copy of the License at
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** http://www.apache.org/licenses/LICENSE-2.0
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** Unless required by applicable law or agreed to in writing, software
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** distributed under the License is distributed on an "AS IS" BASIS,
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** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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** See the License for the specific language governing permissions and
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** limitations under the License.
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*
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**********************************************************************/
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#include "mfcpch.h" //precompiled headers
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#include "hashfn.h"
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/**********************************************************************
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* hash
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*
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* Simple hash function working on power of 2 table sizes.
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* Uses xor function. Needs linear rehash.
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**********************************************************************/
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inT32 hash( //hash function
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inT32 bits, //bits in hash function
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void *key, //key to hash
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inT32 keysize //size of key
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) {
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inT32 bitindex; //current bit count
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uinT32 keybits; //bit buffer
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uinT32 hcode; //current hash code
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uinT32 mask; //bit mask
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mask = (1 << bits) - 1;
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keysize *= 8; //in bits
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bitindex = 0;
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keybits = 0;
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hcode = 0;
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do {
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while (keysize > 0 && bitindex <= 24) {
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keybits |= *((uinT8 *) key) << bitindex;
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key = (uinT8 *) key + 1;
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bitindex += 8;
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keysize -= 8;
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}
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hcode ^= keybits & mask; //key new key
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keybits >>= bits;
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}
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while (keysize > 0);
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return hcode; //initial hash
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}
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