Update #0 - First Release

sources/main/java/com/google/common/base/SmallCharMatcher.java

@@ -0,0 +1,155 @@
+/*
+ * Copyright (C) 2012 The Guava Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.common.base;
+
+import java.util.BitSet;
+
+import com.google.common.annotations.GwtIncompatible;
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.CharMatcher.FastMatcher;
+
+/**
+ * An immutable version of CharMatcher for smallish sets of characters that uses
+ * a hash table with linear probing to check for matches.
+ *
+ * @author Christopher Swenson
+ */
+@GwtIncompatible("no precomputation is done in GWT")
+final class SmallCharMatcher extends FastMatcher {
+	static final int MAX_SIZE = 1023;
+	private final char[] table;
+	private final boolean containsZero;
+	private final long filter;
+
+	private SmallCharMatcher(char[] table, long filter, boolean containsZero, String description) {
+		super(description);
+		this.table = table;
+		this.filter = filter;
+		this.containsZero = containsZero;
+	}
+
+	private static final int C1 = 0xcc9e2d51;
+	private static final int C2 = 0x1b873593;
+
+	/*
+	 * This method was rewritten in Java from an intermediate step of the Murmur
+	 * hash function in
+	 * http://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp, which
+	 * contained the following header:
+	 *
+	 * MurmurHash3 was written by Austin Appleby, and is placed in the public
+	 * domain. The author hereby disclaims copyright to this source code.
+	 */
+	static int smear(int hashCode) {
+		return C2 * Integer.rotateLeft(hashCode * C1, 15);
+	}
+
+	private boolean checkFilter(int c) {
+		return 1 == (1 & (filter >> c));
+	}
+
+	// This is all essentially copied from ImmutableSet, but we have to duplicate
+	// because
+	// of dependencies.
+
+	// Represents how tightly we can pack things, as a maximum.
+	private static final double DESIRED_LOAD_FACTOR = 0.5;
+
+	/**
+	 * Returns an array size suitable for the backing array of a hash table that
+	 * uses open addressing with linear probing in its implementation. The returned
+	 * size is the smallest power of two that can hold setSize elements with the
+	 * desired load factor.
+	 */
+	@VisibleForTesting
+	static int chooseTableSize(int setSize) {
+		if (setSize == 1) {
+			return 2;
+		}
+		// Correct the size for open addressing to match desired load factor.
+		// Round up to the next highest power of 2.
+		int tableSize = Integer.highestOneBit(setSize - 1) << 1;
+		while (tableSize * DESIRED_LOAD_FACTOR < setSize) {
+			tableSize <<= 1;
+		}
+		return tableSize;
+	}
+
+	static CharMatcher from(BitSet chars, String description) {
+		// Compute the filter.
+		long filter = 0;
+		int size = chars.cardinality();
+		boolean containsZero = chars.get(0);
+		// Compute the hash table.
+		char[] table = new char[chooseTableSize(size)];
+		int mask = table.length - 1;
+		for (int c = chars.nextSetBit(0); c != -1; c = chars.nextSetBit(c + 1)) {
+			// Compute the filter at the same time.
+			filter |= 1L << c;
+			int index = smear(c) & mask;
+			while (true) {
+				// Check for empty.
+				if (table[index] == 0) {
+					table[index] = (char) c;
+					break;
+				}
+				// Linear probing.
+				index = (index + 1) & mask;
+			}
+		}
+		return new SmallCharMatcher(table, filter, containsZero, description);
+	}
+
+	@Override
+	public boolean matches(char c) {
+		if (c == 0) {
+			return containsZero;
+		}
+		if (!checkFilter(c)) {
+			return false;
+		}
+		int mask = table.length - 1;
+		int startingIndex = smear(c) & mask;
+		int index = startingIndex;
+		do {
+			// Check for empty.
+			if (table[index] == 0) {
+				return false;
+				// Check for match.
+			} else if (table[index] == c) {
+				return true;
+			} else {
+				// Linear probing.
+				index = (index + 1) & mask;
+			}
+			// Check to see if we wrapped around the whole table.
+		} while (index != startingIndex);
+		return false;
+	}
+
+	@Override
+	void setBits(BitSet table) {
+		if (containsZero) {
+			table.set(0);
+		}
+		for (char c : this.table) {
+			if (c != 0) {
+				table.set(c);
+			}
+		}
+	}
+}