Paul Hsieh's Hash Function. : Hash Code « Development Class « Java
Paul Hsieh's Hash Function.
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//package org.ancora.SharedLibrary;
/**
* Methods for bit manipulation.
*
* @author Joao Bispo
*/
public class Util{
private static final long MASK_16_BITS = 0xFFFFL;
private static final int MASK_BIT_1 = 0x1;
/**
* Paul Hsieh's Hash Function.
*
* @param data data to hash
* @param dataLength length of the data, in bytes
* @param hashedValue previous value of the hash. If it is the start of the
* method, used the length of the data (ex.: 8 bytes).
* @return
*/
public static int superFastHash(long data, int hash) {
int tmp;
//int rem;
//if (len <= 0) {
// return 0;
//}
//rem = len & 3;
//len >>= 2;
//Main Loop
for (int i = 0; i < 4; i += 2) {
// Get lower 16 bits
hash += get16BitsAligned(data, i);
// Calculate some random value with second-lower 16 bits
tmp = (get16BitsAligned(data, i + 1) << 11) ^ hash;
hash = (hash << 16) ^ tmp;
// At this point, it would advance the data, but since it is restricted
// to longs (64-bit values), it is unnecessary).
hash += hash >> 11;
}
// Handle end cases //
// There are no end cases, main loop is done in chuncks of 32 bits.
// Force "avalanching" of final 127 bits //
hash ^= hash << 3;
hash += hash >> 5;
hash ^= hash << 4;
hash += hash >> 17;
hash ^= hash << 25;
hash += hash >> 6;
return hash;
}
/**
* Returns 16 bits from the long number.
*
* @param data
* @param offset one of 0 to 3
* @return
*/
public static int get16BitsAligned(long data, int offset) {
// Normalize offset
offset = offset%4;
//System.out.println("offset:"+offset);
// Align the mask
long mask = MASK_16_BITS << 16*offset;
//System.out.println("Mask:"+Long.toHexString(mask));
//System.out.println("Data:"+Long.toHexString(data));
// Get the bits
long result = data & mask;
// Put bits in position
return (int) (result >>> (16*offset));
}
}
