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Posted to commits@xerces.apache.org by mr...@apache.org on 2012/07/05 03:40:27 UTC
svn commit: r1357443 -
/xerces/xml-commons/trunk/java/external/src/javax/xml/namespace/QName.java
Author: mrglavas
Date: Thu Jul 5 01:40:27 2012
New Revision: 1357443
URL: http://svn.apache.org/viewvc?rev=1357443&view=rev
Log:
Enhancing the QName.hashCode() algorithm to make it more resistant to collisions. The hash function is randomly selected from a large family of possible functions when the class is loaded. Added a system property (javax.xml.namespace.QName.useCompatibleHashCodeAlgorithm) so that users can restore the old behaviour if they require it for some reason.
Modified:
xerces/xml-commons/trunk/java/external/src/javax/xml/namespace/QName.java
Modified: xerces/xml-commons/trunk/java/external/src/javax/xml/namespace/QName.java
URL: http://svn.apache.org/viewvc/xerces/xml-commons/trunk/java/external/src/javax/xml/namespace/QName.java?rev=1357443&r1=1357442&r2=1357443&view=diff
==============================================================================
--- xerces/xml-commons/trunk/java/external/src/javax/xml/namespace/QName.java (original)
+++ xerces/xml-commons/trunk/java/external/src/javax/xml/namespace/QName.java Thu Jul 5 01:40:27 2012
@@ -24,6 +24,7 @@ import java.io.ObjectInputStream;
import java.io.Serializable;
import java.security.AccessController;
import java.security.PrivilegedAction;
+import java.util.Random;
import javax.xml.XMLConstants;
@@ -102,6 +103,51 @@ public class QName implements Serializab
// If 1.0 use compatibility serialVersionUID
serialVersionUID = !"1.0".equals(compatPropValue) ? defaultSerialVersionUID : compatabilitySerialVersionUID;
}
+
+ private static final int MULTIPLIERS_SIZE = 1 << 5;
+ private static final int MULTIPLIERS_MASK = MULTIPLIERS_SIZE - 1;
+
+ private static final int[] hashMultipliers;
+ private static final boolean useDefaultHashCodeAlgorithm;
+ static {
+ boolean _useDefaultHashAlgorithm;
+ try {
+ // use a privileged block for reading a system property
+ String valueUseDefaultHashCodeAlgorithm = (String) AccessController.doPrivileged(
+ new PrivilegedAction() {
+ public Object run() {
+ return System.getProperty("javax.xml.namespace.QName.useCompatibleHashCodeAlgorithm");
+ }
+ }
+ );
+ _useDefaultHashAlgorithm = (valueUseDefaultHashCodeAlgorithm != null && valueUseDefaultHashCodeAlgorithm.equals("1.0")) ? false : true;
+ }
+ catch (Exception exception) {
+ // use default if any Exceptions
+ _useDefaultHashAlgorithm = true;
+ }
+ useDefaultHashCodeAlgorithm = _useDefaultHashAlgorithm;
+ if (useDefaultHashCodeAlgorithm) {
+ hashMultipliers = new int[MULTIPLIERS_SIZE + 1];
+ final int [] PRIMES = {
+ 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59,
+ 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137,
+ 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227,
+ 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313,
+ 317, 331, 337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397, 401, 409, 419,
+ 421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499, 503, 509,
+ 521, 523, 541, 547, 557, 563, 569, 571, 577, 587, 593, 599, 601, 607, 613, 617,
+ 619, 631, 641, 643, 647, 653, 659, 661, 673, 677, 683, 691, 701, 709, 719, 727};
+ // Randomly select multipliers from a set of prime numbers.
+ final Random r = new Random();
+ for (int i = 0; i < hashMultipliers.length; ++i) {
+ hashMultipliers[i] = PRIMES[r.nextInt(PRIMES.length)];
+ }
+ }
+ else {
+ hashMultipliers = null;
+ }
+ }
/**
* <p>Namespace URI of this <code>QName</code>.</p>
@@ -119,6 +165,11 @@ public class QName implements Serializab
private String prefix;
/**
+ * <p>Hash code for this <code>QName<code>.</p>
+ */
+ private transient int hashCode;
+
+ /**
* <p><code>String</code> representation of this <code>QName</code>.</p>
*/
private transient String qNameAsString;
@@ -348,7 +399,17 @@ public class QName implements Serializab
* @return hash code for this <code>QName</code> <code>Object</code>
*/
public final int hashCode() {
- return namespaceURI.hashCode() ^ localPart.hashCode();
+ int _hashCode = hashCode;
+ if (_hashCode == 0) {
+ if (useDefaultHashCodeAlgorithm) {
+ _hashCode = hash(localPart) + hash(namespaceURI) * hashMultipliers[MULTIPLIERS_SIZE];
+ }
+ else {
+ _hashCode = namespaceURI.hashCode() ^ localPart.hashCode();
+ }
+ hashCode = _hashCode;
+ }
+ return _hashCode;
}
/**
@@ -493,4 +554,17 @@ public class QName implements Serializab
prefix = XMLConstants.DEFAULT_NS_PREFIX;
}
}
+
+ /*
+ * Compute hash code of a string using randomly selected multipliers.
+ */
+ private static int hash(String symbol) {
+ int code = 0;
+ final int length = symbol.length();
+ final int[] multipliers = hashMultipliers;
+ for (int i = 0; i < length; ++i) {
+ code = code * multipliers[i & MULTIPLIERS_MASK] + symbol.charAt(i);
+ }
+ return code;
+ }
}
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