gw.util.fingerprint.FP64 Maven / Gradle / Ivy
/*
* Copyright 2014 Guidewire Software, Inc.
*/
package gw.util.fingerprint;
import java.io.IOException;
import java.io.InputStream;
import java.nio.ByteBuffer;
public final class FP64
{
private long _fp;
/** Initializes this object to the fingerprint of the empty string. */
public FP64() {
_fp = IrredPoly;
}
/**
* Initializes this fingerprint to a copy of fp,
* which must be non-null.
*/
public FP64(FP64 fp) {
_fp = fp._fp;
}
/**
* Initializes this object to the fingerprint of the String
* s, which must be non-null.
*/
public FP64(String s) {
this();
extend(s);
}
/**
* Initializes this object to the fingerprint of the character
* array chars, which must be non-null.
*/
public FP64(char[] chars) {
this();
extend(chars, 0, chars.length);
}
/**
* Initializes this object to the fingerprint of the characters
* chars[start]..chars[start+length-1].
*/
public FP64(char[] chars, int start, int length) {
this();
extend(chars, start, length);
}
/**
* Initializes this object to the fingerprint of the byte
* array bytes, which must be non-null.
*/
public FP64(byte[] bytes) {
this();
extend(bytes, 0, bytes.length);
}
/**
* Initializes this object to the fingerprint of the bytes
* bytes[start]..bytes[start+length-1].
*/
public FP64(byte[] bytes, int start, int length) {
this();
extend(bytes, start, length);
}
/**
* Initializes this object to the fingerprint of the bytes
* in stream, which must be non-null.
*
* @throws IOException
* if an error is encountered reading stream.
*/
public FP64(InputStream stream) throws IOException {
this();
extend(stream);
}
/**
* Initializes this object to the fingerprint of the bytes
* in buffer, which must be non-null.
*
* @throws IOException
* if an error is encountered reading stream.
*/
public FP64(ByteBuffer buffer) throws IOException {
this();
extend(buffer);
}
/**
* Returns the value of this fingerprint as a newly-allocated array
* of 8 bytes.
*
* Important: If the output of this function is subsequently
* fingerprinted, the probabilistic guarantee is lost. That is,
* there is a much higher liklihood of fingerprint collisions if
* fingerprint values are themselves fingerprinted in any way.
*/
public byte[] toBytes() {
return toBytes(new byte[8]);
}
/**
* Returns the value of this fingerprint as an 8-byte array.
* Unlike {@link #toBytes()}, this variant does not perform
* an allocation. Instead, the client passes in a buffer into
* which the fingerprint value is written. This can be used
* to get the values of a set of fingerprints without having
* to perform an allocation for each one.
*
* @param buff
* The buffer into which the bytes will be written. This
* array is required to be non-null and exactly 8 bytes in
* length. This buffer is returned.
*/
public byte[] toBytes(/*INOUT*/ byte[] buff) {
assert buff != null;
assert(buff.length == 8) : "buff argument not an array of length 8";
long val = _fp;
for (int i = 0; i < buff.length; i++) {
buff[i] = (byte) (val & 0xFF);
val >>>= 8;
}
return buff;
}
private static final String LEADING_ZEROS = "0000000000000000";
/**
* Returns the value of this fingerprint as an unsigned integer encoded
* in base 16 (hexideicmal), padded with leading zeros to a total length
* of 16 characters.
*
* Important: If the output of this function is subsequently
* fingerprinted, the probabilistic guarantee is lost. That is,
* there is a much higher liklihood of fingerprint collisions if
* fingerprint values are themselves fingerprinted in any way.
*/
public String toHexString() {
String res = Long.toHexString(_fp);
int len = res.length();
if (len < 16) {
res = LEADING_ZEROS.substring(len) + res;
assert res.length() == 16;
}
return res;
}
/**
* Extends this fingerprint by the characters of the String
* s, which must be non-null.
*
* @return
* the resulting fingerprint.
*/
public FP64 extend(String s) {
final int len = s.length();
for (int i = 0; i < len; i++) {
extend(s.charAt(i));
}
return this;
}
/**
* Extends this fingerprint by the characters
* chars[start]..chars[start+length-1].
*
* @return
* the resulting fingerprint.
*/
public FP64 extend(char[] chars) {
extend(chars, 0, chars.length);
return this;
}
/**
* Extends this fingerprint by the characters
* chars[start]..chars[start+length-1].
*
* @return
* the resulting fingerprint.
*/
public FP64 extend(char[] chars, int start, int len) {
int end = start + len;
for (int i = start; i < end; i++) {
extend(chars[i]);
}
return this;
}
/**
* Extends this fingerprint by the bytes
* bytes[offset]..bytes[offset+length-1].
*
* @return
* the resulting fingerprint.
*/
public FP64 extend(byte[] bytes, int start, int len) {
int end = start + len;
for (int i = start; i < end; i++) {
extend(bytes[i]);
}
return this;
}
/**
* Extends this fingerprint by the bytes
*
* @return
* the resulting fingerprint.
*/
public FP64 extend(byte[] bytes) {
for (byte aByte : bytes) {
extend(aByte);
}
return this;
}
/**
* Extends this fingerprint by the integer i.
*
* @return
* the resulting fingerprint.
*/
public FP64 extend(int i) {
extend((byte)((i >>> 24) & 0xFF));
extend((byte)((i >>> 16) & 0xFF));
extend((byte)((i >>> 8) & 0xFF));
extend((byte)((i) & 0xFF));
return this;
}
/**
* Extends this fingerprint by the integer i.
*
* @return
* the resulting fingerprint.
*/
public FP64 extend(long i) {
extend((byte)((i >>> 52) & 0xFF));
extend((byte)((i >>> 48) & 0xFF));
extend((byte)((i >>> 40) & 0xFF));
extend((byte)((i >>> 32) & 0xFF));
extend((byte)((i >>> 24) & 0xFF));
extend((byte)((i >>> 16) & 0xFF));
extend((byte)((i >>> 8) & 0xFF));
extend((byte)((i) & 0xFF));
return this;
}
/**
* Extends this fingerprint by the character c.
*
* @return
* the resulting fingerprint.
*/
public FP64 extend(char c) {
byte b1 = (byte)(c & 0xff);
extend(b1);
byte b2 = (byte) (c >>> 8);
// NOTE pdalbora 23-Jul-2009 -- The following check is intentional. We don't extend the high order byte when it's
// zero, in order to avoid "weakening" the fingerprint of primarily ASCII data by adding unnecessary bits. The
// tradeoff for doing this is that two characters in the low order byte range (<= 0x00FF) will be
// indistinguishable from the corresponding character in the high order byte range (> 0x00FF). For example, the
// character sequence (0x0022, 0x0021) will have the same fingerprint as the character sequence (0x2122). However,
// it would be highly unlikely for this to happen, as ASCII data and non-ASCII data are unlikely to mix together.
// Even in the case where such a sequence pair occurred in two strings, the likelihood of it yielding a collision
// would be very low, when there other characters in the strings.
if (b2 != 0) {
extend(b2);
}
return this;
}
/**
* Extends this fingerprint by the byte b.
*
* @return
* the resulting fingerprint.
*/
public FP64 extend(byte b) {
_fp = (_fp >>> 8) ^ ByteModTable[(b ^ (int)_fp) & 0xFF];
return this;
}
/**
* Extends this fingerprint by the bytes of the stream
* stream, which must be non-null.
*
* @return
* the resulting fingerprint.
*
* @throws IOException
* if an error is encountered reading stream.
*/
public FP64 extend(InputStream stream) throws IOException {
int b;
while ((b = stream.read()) != -1) {
extend((byte) b);
}
return this;
}
public FP64 extend(ByteBuffer buffer) throws IOException {
if (buffer.hasArray()) {
byte[] bytes = buffer.array();
return extend(bytes, 0, bytes.length);
} else {
while (buffer.hasRemaining()) {
extend(buffer.get());
}
}
return this;
}
@Override
public int hashCode() {
return ((int) _fp) ^ ((int)(_fp >>> 32));
}
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (!(obj instanceof FP64)) {
return false;
}
return _fp == ((FP64) obj)._fp;
}
/* This class provides methods that construct fingerprints of
strings of bytes via operations in GF[2^64]. GF[2^64] is represented
as the set polynomials of degree 64 with coefficients in Z(2),
modulo an irreducible polynomial P of degree 64. The internal
representation is a 64-bit Java value of type "long".
Let g(S) be the string obtained from S by prepending the byte 0x80
and appending eight 0x00 bytes. Let f(S) be the polynomial
associated to the string g(S) viewed as a polynomial with
coefficients in the field Z(2). The fingerprint of S is simply
the value f(S) modulo P.
The irreducible polynomial p used as a modulus is
3 7 11 13 16 19 20 24 26 28
1 + x + x + x + x + x + x + x + x + x + x
29 30 36 37 38 41 42 45 46 48
+ x + x + x + x + x + x + x + x + x + x
50 51 52 54 56 57 59 61 62 64
+ x + x + x + x + x + x + x + x + x + x
IrredPoly is its representation. */
// implementation constants
// polynomials are represented with the coefficient for x^0
// in the most significant bit
private static final long Zero = 0L;
private static final long One = 0x8000000000000000L;
private static final long IrredPoly = 0x911498AE0E66BAD6L;
private static final long X63 = 0x1L; // coefficient of x^63
/* This is the table used for extending fingerprints. The
* value ByteModTable[i] is the value to XOR into the finger-
* print value when the byte with value "i" is shifted from
* the top-most byte in the fingerprint. */
private static long[] ByteModTable;
// Initialization code
static {
// Maximum power needed == 64 + 8
int plength = 72;
long[] powerTable = new long[plength];
long t = One;
for (int i = 0; i < plength; i++) {
powerTable[i] = t;
//System.out.println("pow[" + i + "] = " + Long.toHexString(t));
// t = t * x
long mask = ((t & X63) != 0) ? IrredPoly : 0;
t = (t >>> 1) ^ mask;
}
// group bit-wise overflows into bytes
ByteModTable = new long[256];
for (int j = 0; j < ByteModTable.length; j++) {
long v = Zero;
for (int k = 0; k < 9; k++) {
if ((j & (1L << k)) != 0) {
v ^= powerTable[(plength - 1) - k];
}
}
ByteModTable[j] = v;
//System.out.println("ByteModTable[" + j + "] = " + Long.toHexString(v));
}
}
public long getRawFingerprint()
{
return _fp;
}
public String toString() {
return "" + _fp;
}
}