myrabin.java

这是一个URL检索的算法

class MyRabin{

private static final int DEFAULT_IRREDUCIBLE_POLY = 0x0000008D;

   //public static final temp DEFAULT_HASH_FUNCTION =new temp(DEFAULT_IRREDUCIBLE_POLY);


    private static final int P_DEGREE = 32;
    private static final int X_P_DEGREE = 1 << (P_DEGREE - 1);
    private static final int READ_BUFFER_SIZE = 1024;

    private final int P= 0x0000008D;
    private  int[] table32, table40, table48, table56;

    private int hash1;

    MyRabin(){
    	
     final int[] mods = new int[P_DEGREE];

       mods[0] = P;
        for (int i = 1; i < P_DEGREE; i++) {
            final int lastMod = mods[i - 1];

            int thisMod = lastMod << 1;
            if ((lastMod & X_P_DEGREE) != 0) {
                thisMod ^= P;
            }
            mods[i] = thisMod;
        }


        table32 = new int[256];
        table40 = new int[256];
        table48 = new int[256];
        table56 = new int[256];

        for (int i = 0; i < 256; i++) {
            int c = i;
            for (int j = 0; j < 8 && c > 0; j++) {
                if ((c & 1) != 0) {
                    table32[i] ^= mods[j];
                    table40[i] ^= mods[j + 8];
                    table48[i] ^= mods[j + 16];
                    table56[i] ^= mods[j + 24];
                }
                c >>>= 1;
            }
        }
	
      	
    	}//endtemp2


    //private final temp rhf = temp.DEFAULT_HASH_FUNCTION;

   
    protected void engineUpdate(final byte[] input, final int offset, final int len) {
        hash1= hash(input, offset, len, hash1);
    }
    
    protected void engineUpdatec(final char[] input,final int offset,final int len){
    	hash1=hash(input);
    }
    

    protected byte[] engineDigest() {
        final byte[] buf = new byte[4];
        hashToBuf(buf, 0);
        engineReset();
        return buf;
    }

      
    protected void engineReset() {
        hash1= 0;
    }

    private void hashToBuf(final byte[] buf, final int offset) {
        buf[offset] = (byte) (hash1 >> 24);
        buf[offset + 1] = (byte) (hash1 >> 16);
        buf[offset + 2] = (byte) (hash1 >> 8);
        buf[offset + 3] = (byte) hash1;
    }
    
    
        private int computeWShifted(final int w) {
        return table32[w & 0xFF] ^
               table40[(w >>> 8) & 0xFF] ^
               table48[(w >>> 16) & 0xFF] ^
               table56[(w >>> 24) & 0xFF];
    }



    int hash(final byte[] A, final int offset, final int length, int w) {

        int s = offset;

        // First, process a few bytes so that the number of bytes remaining is a multiple of 4.
        // This makes the later loop easier.
        final int starterBytes = length % 4;
        if (starterBytes != 0) {
            final int max = offset + starterBytes;
            while (s < max) {
                w = (w << 8) ^ (A[s] & 0xFF);
                s++;
            }
        }

        final int max = offset + length;
        while (s < max) {
            w = computeWShifted(w) ^
                (A[s] << 24) ^
                ((A[s + 1] & 0xFF) << 16) ^
                ((A[s + 2] & 0xFF) << 8) ^
                (A[s + 3] & 0xFF);
            s += 4;
        }

        return w;
    }


public int hash(final char[] A) {

        int w, s;

        // If an odd number of characters, process the first char so that the number remaining
        // is a multiple of 2. This makes the later loop easier.
        if (A.length % 2 == 1) {
            w = A[0] & 0xFFFF;
            s = 1;
        } else {
            w = 0;
            s = 0;
        }

        while (s < A.length) {
            w = computeWShifted(w) ^ ((A[s] & 0xFFFF) << 16) ^ (A[s + 1] & 0xFFFF);
            s += 2;
        }

        return w;
    }

    
    

}