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/*
* 2-, 3-, and 4-byte hashing
*
* Authors: Lasse Collin <lasse.collin@tukaani.org>
* Igor Pavlov <http://7-zip.org/>
*
* This file has been put into the public domain.
* You can do whatever you want with this file.
*/
package org.tukaani.xz.lz;
import org.tukaani.xz.ArrayCache;
final class Hash234 extends CRC32Hash {
private static final int HASH_2_SIZE = 1 << 10;
private static final int HASH_2_MASK = HASH_2_SIZE - 1;
private static final int HASH_3_SIZE = 1 << 16;
private static final int HASH_3_MASK = HASH_3_SIZE - 1;
private final int hash4Mask;
private final int[] hash2Table;
private final int[] hash3Table;
private final int[] hash4Table;
private final int hash4Size;
private int hash2Value = 0;
private int hash3Value = 0;
private int hash4Value = 0;
static int getHash4Size(int dictSize) {
int h = dictSize - 1;
h |= h >>> 1;
h |= h >>> 2;
h |= h >>> 4;
h |= h >>> 8;
h >>>= 1;
h |= 0xFFFF;
if (h > (1 << 24))
h >>>= 1;
return h + 1;
}
static int getMemoryUsage(int dictSize) {
// Sizes of the hash arrays + a little extra
return (HASH_2_SIZE + HASH_3_SIZE + getHash4Size(dictSize))
/ (1024 / 4) + 4;
}
Hash234(int dictSize, ArrayCache arrayCache) {
hash2Table = arrayCache.getIntArray(HASH_2_SIZE, true);
hash3Table = arrayCache.getIntArray(HASH_3_SIZE, true);
hash4Size = getHash4Size(dictSize);
hash4Table = arrayCache.getIntArray(hash4Size, true);
hash4Mask = hash4Size - 1;
}
void putArraysToCache(ArrayCache arrayCache) {
arrayCache.putArray(hash4Table);
arrayCache.putArray(hash3Table);
arrayCache.putArray(hash2Table);
}
void calcHashes(byte[] buf, int off) {
int temp = crcTable[buf[off] & 0xFF] ^ (buf[off + 1] & 0xFF);
hash2Value = temp & HASH_2_MASK;
temp ^= (buf[off + 2] & 0xFF) << 8;
hash3Value = temp & HASH_3_MASK;
temp ^= crcTable[buf[off + 3] & 0xFF] << 5;
hash4Value = temp & hash4Mask;
}
int getHash2Pos() {
return hash2Table[hash2Value];
}
int getHash3Pos() {
return hash3Table[hash3Value];
}
int getHash4Pos() {
return hash4Table[hash4Value];
}
void updateTables(int pos) {
hash2Table[hash2Value] = pos;
hash3Table[hash3Value] = pos;
hash4Table[hash4Value] = pos;
}
void normalize(int normalizationOffset) {
LZEncoder.normalize(hash2Table, HASH_2_SIZE, normalizationOffset);
LZEncoder.normalize(hash3Table, HASH_3_SIZE, normalizationOffset);
LZEncoder.normalize(hash4Table, hash4Size, normalizationOffset);
}
}
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