org.apache.xerces.utils
Class StringHasher

java.lang.Object
  |
  +--org.apache.xerces.utils.StringHasher

public final class StringHasher

extends java.lang.Object

Algorithm used to hash char arrays (strings). This class was created after it was discovered that parsing some documents was unexpectedly slow due to many different strings hashing to the same 32-bit value using the java.lang.String hash algorithm. The trick seems to be the shift of the top eight bits of the hashcode back down to the bottom to keep them from being rolled out.

Version:

Constructor Summary

StringHasher()

Method Summary

static int	finishHash(int hashcode) finish hashing a partically completed character hashcode
static int	hashChar(int hashcode, int ch) generate partially completed character hashcode.
static int	hashChars(char[] chars, int offset, int length) generate a hashcode for a character array
static int	hashString(java.lang.String str, int strLength) generate a hashcode for a String

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

StringHasher

public StringHasher()

Method Detail

hashString

public static int hashString(java.lang.String str,
                             int strLength)

generate a hashcode for a String

Parameters:

str - the String to hash

strLength - the length of the String to hash

Returns:

hashcode for the String

hashChars

public static int hashChars(char[] chars,
                            int offset,
                            int length)

generate a hashcode for a character array

Parameters:

chars - the array to hash

offset - the offset to start hashing

length - the length of characters to hash

Returns:

hashcode for the character array

hashChar

public static int hashChar(int hashcode,
                           int ch)

generate partially completed character hashcode. this is mean to be iterated over individual characters in order to generate a full hash value

Parameters:

hashcode - a partially completed character hashcode

ch - the character to hash

Returns:

a partially completed character hashcode

See Also:

finishHash(int)

finishHash

public static int finishHash(int hashcode)

finish hashing a partically completed character hashcode

Parameters:

hashcode - a partially completed character hashcode

Returns:

a character hashcode

See Also:

hashChar(int,int)