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;
        // Align the mask
        long mask = MASK_16_BITS << 16*offset;

        // Get the bits
        long result = data & mask;

        // Put bits in position
        return (int) (result >>> (16*offset));


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