LUCENE-3830: use FST instead of recursive HashMaps for MappingCharFilter

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1334623 13f79535-47bb-0310-9956-ffa450edef68

lucene/core/src/java/org/apache/lucene/util/fst/CharSequenceOutputs.java

@@ -0,0 +1,145 @@
+package org.apache.lucene.util.fst;
+
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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.
+ */
+
+import java.io.IOException;
+
+import org.apache.lucene.store.DataInput;
+import org.apache.lucene.store.DataOutput;
+import org.apache.lucene.util.CharsRef;
+
+/**
+ * An FST {@link Outputs} implementation where each output
+ * is a sequence of characters.
+ *
+ * @lucene.experimental
+ */
+
+public final class CharSequenceOutputs extends Outputs<CharsRef> {
+
+  private final static CharsRef NO_OUTPUT = new CharsRef();
+  private final static CharSequenceOutputs singleton = new CharSequenceOutputs();
+
+  private CharSequenceOutputs() {
+  }
+
+  public static CharSequenceOutputs getSingleton() {
+    return singleton;
+  }
+
+  @Override
+  public CharsRef common(CharsRef output1, CharsRef output2) {
+    assert output1 != null;
+    assert output2 != null;
+
+    int pos1 = output1.offset;
+    int pos2 = output2.offset;
+    int stopAt1 = pos1 + Math.min(output1.length, output2.length);
+    while(pos1 < stopAt1) {
+      if (output1.chars[pos1] != output2.chars[pos2]) {
+        break;
+      }
+      pos1++;
+      pos2++;
+    }
+
+    if (pos1 == output1.offset) {
+      // no common prefix
+      return NO_OUTPUT;
+    } else if (pos1 == output1.offset + output1.length) {
+      // output1 is a prefix of output2
+      return output1;
+    } else if (pos2 == output2.offset + output2.length) {
+      // output2 is a prefix of output1
+      return output2;
+    } else {
+      return new CharsRef(output1.chars, output1.offset, pos1-output1.offset);
+    }
+  }
+
+  @Override
+  public CharsRef subtract(CharsRef output, CharsRef inc) {
+    assert output != null;
+    assert inc != null;
+    if (inc == NO_OUTPUT) {
+      // no prefix removed
+      return output;
+    } else if (inc.length == output.length) {
+      // entire output removed
+      return NO_OUTPUT;
+    } else {
+      assert inc.length < output.length: "inc.length=" + inc.length + " vs output.length=" + output.length;
+      assert inc.length > 0;
+      return new CharsRef(output.chars, output.offset + inc.length, output.length-inc.length);
+    }
+  }
+
+  @Override
+  public CharsRef add(CharsRef prefix, CharsRef output) {
+    assert prefix != null;
+    assert output != null;
+    if (prefix == NO_OUTPUT) {
+      return output;
+    } else if (output == NO_OUTPUT) {
+      return prefix;
+    } else {
+      assert prefix.length > 0;
+      assert output.length > 0;
+      CharsRef result = new CharsRef(prefix.length + output.length);
+      System.arraycopy(prefix.chars, prefix.offset, result.chars, 0, prefix.length);
+      System.arraycopy(output.chars, output.offset, result.chars, prefix.length, output.length);
+      result.length = prefix.length + output.length;
+      return result;
+    }
+  }
+
+  @Override
+  public void write(CharsRef prefix, DataOutput out) throws IOException {
+    assert prefix != null;
+    out.writeVInt(prefix.length);
+    // TODO: maybe UTF8?
+    for(int idx=0;idx<prefix.length;idx++) {
+      out.writeVInt(prefix.chars[prefix.offset+idx]);
+    }
+  }
+
+  @Override
+  public CharsRef read(DataInput in) throws IOException {
+    final int len = in.readVInt();
+    if (len == 0) {
+      return NO_OUTPUT;
+    } else {
+      final CharsRef output = new CharsRef(len);
+      for(int idx=0;idx<len;idx++) {
+        output.chars[idx] = (char) in.readVInt();
+      }
+      output.length = len;
+      return output;
+    }
+  }
+
+  @Override
+  public CharsRef getNoOutput() {
+    return NO_OUTPUT;
+  }
+
+  @Override
+  public String outputToString(CharsRef output) {
+    return output.toString();
+  }
+}