X-Git-Url: https://git.mdrn.pl/pylucene.git/blobdiff_plain/a2e61f0c04805cfcb8706176758d1283c7e3a55c..aaeed5504b982cf3545252ab528713250aa33eed:/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/util/fst/FST.java

diff --git a/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/util/fst/FST.java b/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/util/fst/FST.java
new file mode 100644
index 0000000..f312e84
--- /dev/null
+++ b/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/util/fst/FST.java
@@ -0,0 +1,940 @@
+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.ArrayUtil;
+import org.apache.lucene.util.CodecUtil;
+import org.apache.lucene.util.fst.Builder.UnCompiledNode;
+
+// TODO: if FST is pure prefix trie we can do a more compact
+// job, ie, once we are at a 'suffix only', just store the
+// completion labels as a string not as a series of arcs.
+
+// NOTE: while the FST is able to represent a non-final
+// dead-end state (NON_FINAL_END_NODE=0), the layers above
+// (FSTEnum, Util) have problems with this!!
+
+/** Represents an FST using a compact byte[] format.
+ *  <p> The format is similar to what's used by Morfologik
+ *  (http://sourceforge.net/projects/morfologik).
+ *
+ *  <p><b>NOTE</b>: the FST cannot be larger than ~2.1 GB
+ *  because it uses int to address the byte[].
+ *
+ * @lucene.experimental
+ */
+public class FST<T> {
+  public static enum INPUT_TYPE {BYTE1, BYTE2, BYTE4};
+  public final INPUT_TYPE inputType;
+
+  private final static int BIT_FINAL_ARC = 1 << 0;
+  private final static int BIT_LAST_ARC = 1 << 1;
+  private final static int BIT_TARGET_NEXT = 1 << 2;
+  private final static int BIT_STOP_NODE = 1 << 3;
+  private final static int BIT_ARC_HAS_OUTPUT = 1 << 4;
+  private final static int BIT_ARC_HAS_FINAL_OUTPUT = 1 << 5;
+
+  // Arcs are stored as fixed-size (per entry) array, so
+  // that we can find an arc using binary search.  We do
+  // this when number of arcs is > NUM_ARCS_ARRAY:
+  private final static int BIT_ARCS_AS_FIXED_ARRAY = 1 << 6;
+
+  /**
+   * @see #shouldExpand(UnCompiledNode)
+   */
+  final static int FIXED_ARRAY_SHALLOW_DISTANCE = 3; // 0 => only root node.
+
+  /**
+   * @see #shouldExpand(UnCompiledNode)
+   */
+  final static int FIXED_ARRAY_NUM_ARCS_SHALLOW = 5;
+
+  /**
+   * @see #shouldExpand(UnCompiledNode)
+   */
+  final static int FIXED_ARRAY_NUM_ARCS_DEEP = 10;
+
+  private int[] bytesPerArc = new int[0];
+
+  // Increment version to change it
+  private final static String FILE_FORMAT_NAME = "FST";
+  private final static int VERSION_START = 0;
+
+  /** Changed numBytesPerArc for array'd case from byte to int. */
+  private final static int VERSION_INT_NUM_BYTES_PER_ARC = 1;
+
+  private final static int VERSION_CURRENT = VERSION_INT_NUM_BYTES_PER_ARC;
+
+  // Never serialized; just used to represent the virtual
+  // final node w/ no arcs:
+  private final static int FINAL_END_NODE = -1;
+
+  // Never serialized; just used to represent the virtual
+  // non-final node w/ no arcs:
+  private final static int NON_FINAL_END_NODE = 0;
+
+  // if non-null, this FST accepts the empty string and
+  // produces this output
+  T emptyOutput;
+  private byte[] emptyOutputBytes;
+
+  private byte[] bytes;
+  int byteUpto = 0;
+
+  private int startNode = -1;
+
+  public final Outputs<T> outputs;
+
+  private int lastFrozenNode;
+
+  private final T NO_OUTPUT;
+
+  public int nodeCount;
+  public int arcCount;
+  public int arcWithOutputCount;
+
+  // If arc has this label then that arc is final/accepted
+  public static final int END_LABEL = -1;
+
+  private Arc<T> cachedRootArcs[];
+
+  public final static class Arc<T> {
+    public int label;
+    public T output;
+
+    int target;
+
+    byte flags;
+    public T nextFinalOutput;
+    int nextArc;
+
+    // This is non-zero if current arcs are fixed array:
+    int posArcsStart;
+    int bytesPerArc;
+    int arcIdx;
+    int numArcs;
+
+    /** Returns this */
+    public Arc<T> copyFrom(Arc<T> other) {
+      label = other.label;
+      target = other.target;
+      flags = other.flags;
+      output = other.output;
+      nextFinalOutput = other.nextFinalOutput;
+      nextArc = other.nextArc;
+      if (other.bytesPerArc != 0) {
+        bytesPerArc = other.bytesPerArc;
+        posArcsStart = other.posArcsStart;
+        arcIdx = other.arcIdx;
+        numArcs = other.numArcs;
+      } else {
+        bytesPerArc = 0;
+      }
+      return this;
+    }
+
+    boolean flag(int flag) {
+      return FST.flag(flags, flag);
+    }
+
+    public boolean isLast() {
+      return flag(BIT_LAST_ARC);
+    }
+
+    public boolean isFinal() {
+      return flag(BIT_FINAL_ARC);
+    }
+  };
+
+  static boolean flag(int flags, int bit) {
+    return (flags & bit) != 0;
+  }
+
+  private final BytesWriter writer;
+
+  // make a new empty FST, for building
+  public FST(INPUT_TYPE inputType, Outputs<T> outputs) {
+    this.inputType = inputType;
+    this.outputs = outputs;
+    bytes = new byte[128];
+    NO_OUTPUT = outputs.getNoOutput();
+    
+    writer = new BytesWriter();
+
+    emptyOutput = null;
+  }
+
+  // create an existing FST
+  public FST(DataInput in, Outputs<T> outputs) throws IOException {
+    this.outputs = outputs;
+    writer = null;
+    CodecUtil.checkHeader(in, FILE_FORMAT_NAME, VERSION_INT_NUM_BYTES_PER_ARC, VERSION_INT_NUM_BYTES_PER_ARC);
+    if (in.readByte() == 1) {
+      // accepts empty string
+      int numBytes = in.readVInt();
+      // messy
+      bytes = new byte[numBytes];
+      in.readBytes(bytes, 0, numBytes);
+      emptyOutput = outputs.read(getBytesReader(numBytes-1));
+    } else {
+      emptyOutput = null;
+    }
+    final byte t = in.readByte();
+    switch(t) {
+      case 0:
+        inputType = INPUT_TYPE.BYTE1;
+        break;
+      case 1:
+        inputType = INPUT_TYPE.BYTE2;
+        break;
+      case 2:
+        inputType = INPUT_TYPE.BYTE4;
+        break;
+    default:
+      throw new IllegalStateException("invalid input type " + t);
+    }
+    startNode = in.readVInt();
+    nodeCount = in.readVInt();
+    arcCount = in.readVInt();
+    arcWithOutputCount = in.readVInt();
+
+    bytes = new byte[in.readVInt()];
+    in.readBytes(bytes, 0, bytes.length);
+    NO_OUTPUT = outputs.getNoOutput();
+
+    cacheRootArcs();
+  }
+
+  public INPUT_TYPE getInputType() {
+    return inputType;
+  }
+
+  /** Returns bytes used to represent the FST */
+  public int sizeInBytes() {
+    return bytes.length;
+  }
+
+  void finish(int startNode) throws IOException {
+    if (startNode == FINAL_END_NODE && emptyOutput != null) {
+      startNode = 0;
+    }
+    if (this.startNode != -1) {
+      throw new IllegalStateException("already finished");
+    }
+    byte[] finalBytes = new byte[writer.posWrite];
+    System.arraycopy(bytes, 0, finalBytes, 0, writer.posWrite);
+    bytes = finalBytes;
+    this.startNode = startNode;
+
+    cacheRootArcs();
+  }
+
+  // Caches first 128 labels
+  @SuppressWarnings("unchecked")
+  private void cacheRootArcs() throws IOException {
+    cachedRootArcs = (FST.Arc<T>[]) new FST.Arc[0x80];
+    final FST.Arc<T> arc = new FST.Arc<T>();
+    getFirstArc(arc);
+    final BytesReader in = getBytesReader(0);
+    if (targetHasArcs(arc)) {
+      readFirstRealArc(arc.target, arc);
+      while(true) {
+        assert arc.label != END_LABEL;
+        if (arc.label < cachedRootArcs.length) {
+          cachedRootArcs[arc.label] = new Arc<T>().copyFrom(arc);
+        } else {
+          break;
+        }
+        if (arc.isLast()) {
+          break;
+        }
+        readNextRealArc(arc, in);
+      }
+    }
+  }
+
+  void setEmptyOutput(T v) throws IOException {
+    if (emptyOutput != null) {
+      emptyOutput = outputs.merge(emptyOutput, v);
+    } else {
+      emptyOutput = v;
+    }
+
+    // TODO: this is messy -- replace with sillyBytesWriter; maybe make
+    // bytes private
+    final int posSave = writer.posWrite;
+    outputs.write(emptyOutput, writer);
+    emptyOutputBytes = new byte[writer.posWrite-posSave];
+
+    // reverse
+    final int stopAt = (writer.posWrite - posSave)/2;
+    int upto = 0;
+    while(upto < stopAt) {
+      final byte b = bytes[posSave + upto];
+      bytes[posSave+upto] = bytes[writer.posWrite-upto-1];
+      bytes[writer.posWrite-upto-1] = b;
+      upto++;
+    }
+    System.arraycopy(bytes, posSave, emptyOutputBytes, 0, writer.posWrite-posSave);
+    writer.posWrite = posSave;
+  }
+
+  public void save(DataOutput out) throws IOException {
+    if (startNode == -1) {
+      throw new IllegalStateException("call finish first");
+    }
+    CodecUtil.writeHeader(out, FILE_FORMAT_NAME, VERSION_CURRENT);
+    // TODO: really we should encode this as an arc, arriving
+    // to the root node, instead of special casing here:
+    if (emptyOutput != null) {
+      out.writeByte((byte) 1);
+      out.writeVInt(emptyOutputBytes.length);
+      out.writeBytes(emptyOutputBytes, 0, emptyOutputBytes.length);
+    } else {
+      out.writeByte((byte) 0);
+    }
+    final byte t;
+    if (inputType == INPUT_TYPE.BYTE1) {
+      t = 0;
+    } else if (inputType == INPUT_TYPE.BYTE2) {
+      t = 1;
+    } else {
+      t = 2;
+    }
+    out.writeByte(t);
+    out.writeVInt(startNode);
+    out.writeVInt(nodeCount);
+    out.writeVInt(arcCount);
+    out.writeVInt(arcWithOutputCount);
+    out.writeVInt(bytes.length);
+    out.writeBytes(bytes, 0, bytes.length);
+  }
+
+  private void writeLabel(int v) throws IOException {
+    assert v >= 0: "v=" + v;
+    if (inputType == INPUT_TYPE.BYTE1) {
+      assert v <= 255: "v=" + v;
+      writer.writeByte((byte) v);
+    } else if (inputType == INPUT_TYPE.BYTE2) {
+      assert v <= 65535: "v=" + v;
+      writer.writeVInt(v);
+    } else {
+      //writeInt(v);
+      writer.writeVInt(v);
+    }
+  }
+
+  int readLabel(DataInput in) throws IOException {
+    final int v;
+    if (inputType == INPUT_TYPE.BYTE1) {
+      v = in.readByte()&0xFF;
+    } else { 
+      v = in.readVInt();
+    }
+    return v;
+  }
+
+  // returns true if the node at this address has any
+  // outgoing arcs
+  public boolean targetHasArcs(Arc<T> arc) {
+    return arc.target > 0;
+  }
+
+  // serializes new node by appending its bytes to the end
+  // of the current byte[]
+  int addNode(Builder.UnCompiledNode<T> node) throws IOException {
+    //System.out.println("FST.addNode pos=" + posWrite + " numArcs=" + node.numArcs);
+    if (node.numArcs == 0) {
+      if (node.isFinal) {
+        return FINAL_END_NODE;
+      } else {
+        return NON_FINAL_END_NODE;
+      }
+    }
+
+    int startAddress = writer.posWrite;
+    //System.out.println("  startAddr=" + startAddress);
+
+    final boolean doFixedArray = shouldExpand(node);
+    final int fixedArrayStart;
+    if (doFixedArray) {
+      if (bytesPerArc.length < node.numArcs) {
+        bytesPerArc = new int[ArrayUtil.oversize(node.numArcs, 1)];
+      }
+      // write a "false" first arc:
+      writer.writeByte((byte) BIT_ARCS_AS_FIXED_ARRAY);
+      writer.writeVInt(node.numArcs);
+      // placeholder -- we'll come back and write the number
+      // of bytes per arc (int) here:
+      // TODO: we could make this a vInt instead
+      writer.writeInt(0);
+      fixedArrayStart = writer.posWrite;
+      //System.out.println("  do fixed arcs array arcsStart=" + fixedArrayStart);
+    } else {
+      fixedArrayStart = 0;
+    }
+
+    nodeCount++;
+    arcCount += node.numArcs;
+    
+    final int lastArc = node.numArcs-1;
+
+    int lastArcStart = writer.posWrite;
+    int maxBytesPerArc = 0;
+    for(int arcIdx=0;arcIdx<node.numArcs;arcIdx++) {
+      final Builder.Arc<T> arc = node.arcs[arcIdx];
+      final Builder.CompiledNode target = (Builder.CompiledNode) arc.target;
+      int flags = 0;
+
+      if (arcIdx == lastArc) {
+        flags += BIT_LAST_ARC;
+      }
+
+      if (lastFrozenNode == target.address && !doFixedArray) {
+        flags += BIT_TARGET_NEXT;
+      }
+
+      if (arc.isFinal) {
+        flags += BIT_FINAL_ARC;
+        if (arc.nextFinalOutput != NO_OUTPUT) {
+          flags += BIT_ARC_HAS_FINAL_OUTPUT;
+        }
+      } else {
+        assert arc.nextFinalOutput == NO_OUTPUT;
+      }
+
+      boolean targetHasArcs = target.address > 0;
+
+      if (!targetHasArcs) {
+        flags += BIT_STOP_NODE;
+      }
+
+      if (arc.output != NO_OUTPUT) {
+        flags += BIT_ARC_HAS_OUTPUT;
+      }
+
+      writer.writeByte((byte) flags);
+      writeLabel(arc.label);
+
+      //System.out.println("  write arc: label=" + arc.label + " flags=" + flags);
+
+      if (arc.output != NO_OUTPUT) {
+        outputs.write(arc.output, writer);
+        arcWithOutputCount++;
+      }
+      if (arc.nextFinalOutput != NO_OUTPUT) {
+        outputs.write(arc.nextFinalOutput, writer);
+      }
+
+      if (targetHasArcs && (doFixedArray || lastFrozenNode != target.address)) {
+        assert target.address > 0;
+        writer.writeInt(target.address);
+      }
+
+      // just write the arcs "like normal" on first pass,
+      // but record how many bytes each one took, and max
+      // byte size:
+      if (doFixedArray) {
+        bytesPerArc[arcIdx] = writer.posWrite - lastArcStart;
+        lastArcStart = writer.posWrite;
+        maxBytesPerArc = Math.max(maxBytesPerArc, bytesPerArc[arcIdx]);
+        //System.out.println("    bytes=" + bytesPerArc[arcIdx]);
+      }
+    }
+
+    // TODO: if arc'd arrays will be "too wasteful" by some
+    // measure, eg if arcs have vastly different sized
+    // outputs, then we should selectively disable array for
+    // such cases
+
+    if (doFixedArray) {
+      assert maxBytesPerArc > 0;
+      // 2nd pass just "expands" all arcs to take up a fixed
+      // byte size
+      final int sizeNeeded = fixedArrayStart + node.numArcs * maxBytesPerArc;
+      bytes = ArrayUtil.grow(bytes, sizeNeeded);
+      // TODO: we could make this a vInt instead
+      bytes[fixedArrayStart-4] = (byte) (maxBytesPerArc >> 24);
+      bytes[fixedArrayStart-3] = (byte) (maxBytesPerArc >> 16);
+      bytes[fixedArrayStart-2] = (byte) (maxBytesPerArc >> 8);
+      bytes[fixedArrayStart-1] = (byte) maxBytesPerArc;
+
+      // expand the arcs in place, backwards
+      int srcPos = writer.posWrite;
+      int destPos = fixedArrayStart + node.numArcs*maxBytesPerArc;
+      writer.posWrite = destPos;
+      for(int arcIdx=node.numArcs-1;arcIdx>=0;arcIdx--) {
+        //System.out.println("  repack arcIdx=" + arcIdx + " srcPos=" + srcPos + " destPos=" + destPos);
+        destPos -= maxBytesPerArc;
+        srcPos -= bytesPerArc[arcIdx];
+        if (srcPos != destPos) {
+          assert destPos > srcPos;
+          System.arraycopy(bytes, srcPos, bytes, destPos, bytesPerArc[arcIdx]);
+        }
+      }
+    }
+
+    // reverse bytes in-place; we do this so that the
+    // "BIT_TARGET_NEXT" opto can work, ie, it reads the
+    // node just before the current one
+    final int endAddress = lastFrozenNode = writer.posWrite - 1;
+
+    int left = startAddress;
+    int right = endAddress;
+    while (left < right) {
+      final byte b = bytes[left];
+      bytes[left++] = bytes[right];
+      bytes[right--] = b;
+    }
+
+    return endAddress;
+  }
+
+  /** Fills virtual 'start' arc, ie, an empty incoming arc to
+   *  the FST's start node */
+  public Arc<T> getFirstArc(Arc<T> arc) {
+    if (emptyOutput != null) {
+      arc.flags = BIT_FINAL_ARC | BIT_LAST_ARC;
+      arc.nextFinalOutput = emptyOutput;
+    } else {
+      arc.flags = BIT_LAST_ARC;
+      arc.nextFinalOutput = NO_OUTPUT;
+    }
+    arc.output = NO_OUTPUT;
+
+    // If there are no nodes, ie, the FST only accepts the
+    // empty string, then startNode is 0, and then readFirstTargetArc
+    arc.target = startNode;
+    return arc;
+  }
+
+  /** Follows the <code>follow</code> arc and reads the last
+   *  arc of its target; this changes the provided
+   *  <code>arc</code> (2nd arg) in-place and returns it.
+   * 
+   * @return Returns the second argument
+   * (<code>arc</code>). */
+  public Arc<T> readLastTargetArc(Arc<T> follow, Arc<T> arc) throws IOException {
+    //System.out.println("readLast");
+    if (!targetHasArcs(follow)) {
+      //System.out.println("  end node");
+      assert follow.isFinal();
+      arc.label = END_LABEL;
+      arc.output = follow.nextFinalOutput;
+      arc.flags = BIT_LAST_ARC;
+      return arc;
+    } else {
+      final BytesReader in = getBytesReader(follow.target);
+      arc.flags = in.readByte();
+      if (arc.flag(BIT_ARCS_AS_FIXED_ARRAY)) {
+        // array: jump straight to end
+        arc.numArcs = in.readVInt();
+        arc.bytesPerArc = in.readInt();
+        //System.out.println("  array numArcs=" + arc.numArcs + " bpa=" + arc.bytesPerArc);
+        arc.posArcsStart = in.pos;
+        arc.arcIdx = arc.numArcs - 2;
+      } else {
+        // non-array: linear scan
+        arc.bytesPerArc = 0;
+        //System.out.println("  scan");
+        while(!arc.isLast()) {
+          // skip this arc:
+          readLabel(in);
+          if (arc.flag(BIT_ARC_HAS_OUTPUT)) {
+            outputs.read(in);
+          }
+          if (arc.flag(BIT_ARC_HAS_FINAL_OUTPUT)) {
+            outputs.read(in);
+          }
+          if (arc.flag(BIT_STOP_NODE)) {
+          } else if (arc.flag(BIT_TARGET_NEXT)) {
+          } else {
+            in.pos -= 4;
+          }
+          arc.flags = in.readByte();
+        }
+        arc.nextArc = in.pos+1;
+      }
+      readNextRealArc(arc, in);
+      assert arc.isLast();
+      return arc;
+    }
+  }
+
+  /**
+   * Follow the <code>follow</code> arc and read the first arc of its target;
+   * this changes the provided <code>arc</code> (2nd arg) in-place and returns
+   * it.
+   * 
+   * @return Returns the second argument (<code>arc</code>).
+   */
+  public Arc<T> readFirstTargetArc(Arc<T> follow, Arc<T> arc) throws IOException {
+    //int pos = address;
+    //System.out.println("    readFirstTarget follow.target=" + follow.target + " isFinal=" + follow.isFinal());
+    if (follow.isFinal()) {
+      // Insert "fake" final first arc:
+      arc.label = END_LABEL;
+      arc.output = follow.nextFinalOutput;
+      if (follow.target <= 0) {
+        arc.flags = BIT_LAST_ARC;
+      } else {
+        arc.flags = 0;
+        arc.nextArc = follow.target;
+      }
+      //System.out.println("    insert isFinal; nextArc=" + follow.target + " isLast=" + arc.isLast() + " output=" + outputs.outputToString(arc.output));
+      return arc;
+    } else {
+      return readFirstRealArc(follow.target, arc);
+    }
+  }
+
+  // Not private because NodeHash needs access:
+  Arc<T> readFirstRealArc(int address, Arc<T> arc) throws IOException {
+
+    final BytesReader in = getBytesReader(address);
+
+    arc.flags = in.readByte();
+
+    if (arc.flag(BIT_ARCS_AS_FIXED_ARRAY)) {
+      //System.out.println("  fixedArray");
+      // this is first arc in a fixed-array
+      arc.numArcs = in.readVInt();
+      arc.bytesPerArc = in.readInt();
+      arc.arcIdx = -1;
+      arc.nextArc = arc.posArcsStart = in.pos;
+      //System.out.println("  bytesPer=" + arc.bytesPerArc + " numArcs=" + arc.numArcs + " arcsStart=" + pos);
+    } else {
+      arc.nextArc = address;
+      arc.bytesPerArc = 0;
+    }
+    return readNextRealArc(arc, in);
+  }
+
+  /**
+   * Checks if <code>arc</code>'s target state is in expanded (or vector) format. 
+   * 
+   * @return Returns <code>true</code> if <code>arc</code> points to a state in an
+   * expanded array format.
+   */
+  boolean isExpandedTarget(Arc<T> follow) throws IOException {
+    if (!targetHasArcs(follow)) {
+      return false;
+    } else {
+      final BytesReader in = getBytesReader(follow.target);
+      final byte b = in.readByte();
+      return (b & BIT_ARCS_AS_FIXED_ARRAY) != 0;
+    }
+  }
+
+  /** In-place read; returns the arc. */
+  public Arc<T> readNextArc(Arc<T> arc) throws IOException {
+    if (arc.label == END_LABEL) {
+      // This was a fake inserted "final" arc
+      if (arc.nextArc <= 0) {
+        // This arc went to virtual final node, ie has no outgoing arcs
+        return null;
+      }
+      return readFirstRealArc(arc.nextArc, arc);
+    } else {
+      return readNextRealArc(arc, getBytesReader(0));
+    }
+  }
+
+  /** Peeks at next arc's label; does not alter arc.  Do
+   *  not call this if arc.isLast()! */
+  public int readNextArcLabel(Arc<T> arc) throws IOException {
+    assert !arc.isLast();
+
+    final BytesReader in;
+    if (arc.label == END_LABEL) {
+      //System.out.println("    nextArc fake " + arc.nextArc);
+      in = getBytesReader(arc.nextArc);
+      byte flags = bytes[in.pos];
+      if (flag(flags, BIT_ARCS_AS_FIXED_ARRAY)) {
+        //System.out.println("    nextArc fake array");
+        in.pos--;
+        in.readVInt();
+        in.readInt();
+      }
+    } else {
+      if (arc.bytesPerArc != 0) {
+        //System.out.println("    nextArc real array");
+        // arcs are at fixed entries
+        in = getBytesReader(arc.posArcsStart - (1+arc.arcIdx)*arc.bytesPerArc);
+      } else {
+        // arcs are packed
+        //System.out.println("    nextArc real packed");
+        in = getBytesReader(arc.nextArc);
+      }
+    }
+    // skip flags
+    in.readByte();
+    return readLabel(in);
+  }
+
+  Arc<T> readNextRealArc(Arc<T> arc, final BytesReader in) throws IOException {
+    // this is a continuing arc in a fixed array
+    if (arc.bytesPerArc != 0) {
+      // arcs are at fixed entries
+      arc.arcIdx++;
+      assert arc.arcIdx < arc.numArcs;
+      in.pos = arc.posArcsStart - arc.arcIdx*arc.bytesPerArc;
+    } else {
+      // arcs are packed
+      in.pos = arc.nextArc;
+    }
+    arc.flags = in.readByte();
+    arc.label = readLabel(in);
+
+    if (arc.flag(BIT_ARC_HAS_OUTPUT)) {
+      arc.output = outputs.read(in);
+    } else {
+      arc.output = outputs.getNoOutput();
+    }
+
+    if (arc.flag(BIT_ARC_HAS_FINAL_OUTPUT)) {
+      arc.nextFinalOutput = outputs.read(in);
+    } else {
+      arc.nextFinalOutput = outputs.getNoOutput();
+    }
+
+    if (arc.flag(BIT_STOP_NODE)) {
+      if (arc.flag(BIT_FINAL_ARC)) {
+        arc.target = FINAL_END_NODE;
+      } else {
+        arc.target = NON_FINAL_END_NODE;
+      }
+      arc.nextArc = in.pos;
+    } else if (arc.flag(BIT_TARGET_NEXT)) {
+      arc.nextArc = in.pos;
+      if (!arc.flag(BIT_LAST_ARC)) {
+        if (arc.bytesPerArc == 0) {
+          // must scan
+          seekToNextNode(in);
+        } else {
+          in.pos = arc.posArcsStart - arc.bytesPerArc * arc.numArcs;
+        }
+      }
+      arc.target = in.pos;
+    } else {
+      arc.target = in.readInt();
+      arc.nextArc = in.pos;
+    }
+
+    return arc;
+  }
+
+  /** Finds an arc leaving the incoming arc, replacing the arc in place.
+   *  This returns null if the arc was not found, else the incoming arc. */
+  public Arc<T> findTargetArc(int labelToMatch, Arc<T> follow, Arc<T> arc) throws IOException {
+    assert cachedRootArcs != null;
+    // Short-circuit if this arc is in the root arc cache:
+    if (follow.target == startNode && labelToMatch != END_LABEL && labelToMatch < cachedRootArcs.length) {
+      final Arc<T> result = cachedRootArcs[labelToMatch];
+      if (result == null) {
+        return result;
+      } else {
+        arc.copyFrom(result);
+        return arc;
+      }
+    }
+ 
+    if (labelToMatch == END_LABEL) {
+      if (follow.isFinal()) {
+        arc.output = follow.nextFinalOutput;
+        arc.label = END_LABEL;
+        return arc;
+      } else {
+        return null;
+      }
+    }
+
+    if (!targetHasArcs(follow)) {
+      return null;
+    }
+
+    // TODO: maybe make an explicit thread state that holds
+    // reusable stuff eg BytesReader:
+    final BytesReader in = getBytesReader(follow.target);
+
+    // System.out.println("fta label=" + (char) labelToMatch);
+
+    if ((in.readByte() & BIT_ARCS_AS_FIXED_ARRAY) != 0) {
+      // Arcs are full array; do binary search:
+      arc.numArcs = in.readVInt();
+      //System.out.println("  bs " + arc.numArcs);
+      arc.bytesPerArc = in.readInt();
+      arc.posArcsStart = in.pos;
+      int low = 0;
+      int high = arc.numArcs-1;
+      while (low <= high) {
+        //System.out.println("    cycle");
+        int mid = (low + high) >>> 1;
+        in.pos = arc.posArcsStart - arc.bytesPerArc*mid - 1;
+        int midLabel = readLabel(in);
+        final int cmp = midLabel - labelToMatch;
+        if (cmp < 0)
+          low = mid + 1;
+        else if (cmp > 0)
+          high = mid - 1;
+        else {
+          arc.arcIdx = mid-1;
+          //System.out.println("    found!");
+          return readNextRealArc(arc, in);
+        }
+      }
+
+      return null;
+    }
+
+    // Linear scan
+    readFirstTargetArc(follow, arc);
+    while(true) {
+      //System.out.println("  non-bs cycle");
+      // TODO: we should fix this code to not have to create
+      // object for the output of every arc we scan... only
+      // for the matching arc, if found
+      if (arc.label == labelToMatch) {
+        //System.out.println("    found!");
+        return arc;
+      } else if (arc.label > labelToMatch) {
+        return null;
+      } else if (arc.isLast()) {
+        return null;
+      } else {
+        readNextArc(arc);
+      }
+    }
+  }
+
+  private void seekToNextNode(BytesReader in) throws IOException {
+
+    while(true) {
+
+      final int flags = in.readByte();
+      readLabel(in);
+
+      if (flag(flags, BIT_ARC_HAS_OUTPUT)) {
+        outputs.read(in);
+      }
+
+      if (flag(flags, BIT_ARC_HAS_FINAL_OUTPUT)) {
+        outputs.read(in);
+      }
+
+      if (!flag(flags, BIT_STOP_NODE) && !flag(flags, BIT_TARGET_NEXT)) {
+        in.readInt();
+      }
+
+      if (flag(flags, BIT_LAST_ARC)) {
+        return;
+      }
+    }
+  }
+
+  public int getNodeCount() {
+    // 1+ in order to count the -1 implicit final node
+    return 1+nodeCount;
+  }
+  
+  public int getArcCount() {
+    return arcCount;
+  }
+
+  public int getArcWithOutputCount() {
+    return arcWithOutputCount;
+  }
+  
+  /**
+   * Nodes will be expanded if their depth (distance from the root node) is
+   * &lt;= this value and their number of arcs is &gt;=
+   * {@link #FIXED_ARRAY_NUM_ARCS_SHALLOW}.
+   * 
+   * <p>
+   * Fixed array consumes more RAM but enables binary search on the arcs
+   * (instead of a linear scan) on lookup by arc label.
+   * 
+   * @return <code>true</code> if <code>node</code> should be stored in an
+   *         expanded (array) form.
+   * 
+   * @see #FIXED_ARRAY_NUM_ARCS_DEEP
+   * @see Builder.UnCompiledNode#depth
+   */
+  private boolean shouldExpand(UnCompiledNode<T> node) {
+    return (node.depth <= FIXED_ARRAY_SHALLOW_DISTANCE && node.numArcs >= FIXED_ARRAY_NUM_ARCS_SHALLOW) || 
+            node.numArcs >= FIXED_ARRAY_NUM_ARCS_DEEP;
+  }
+
+  // Non-static: writes to FST's byte[]
+  class BytesWriter extends DataOutput {
+    int posWrite;
+
+    public BytesWriter() {
+      // pad: ensure no node gets address 0 which is reserved to mean
+      // the stop state w/ no arcs
+      posWrite = 1;
+    }
+
+    @Override
+    public void writeByte(byte b) {
+      if (bytes.length == posWrite) {
+        bytes = ArrayUtil.grow(bytes);
+      }
+      assert posWrite < bytes.length: "posWrite=" + posWrite + " bytes.length=" + bytes.length;
+      bytes[posWrite++] = b;
+    }
+
+    @Override
+    public void writeBytes(byte[] b, int offset, int length) {
+      final int size = posWrite + length;
+      bytes = ArrayUtil.grow(bytes, size);
+      System.arraycopy(b, offset, bytes, posWrite, length);
+      posWrite += length;
+    }
+  }
+
+  final BytesReader getBytesReader(int pos) {
+    // TODO: maybe re-use via ThreadLocal?
+    return new BytesReader(pos);
+  }
+
+  // Non-static: reads byte[] from FST
+  final class BytesReader extends DataInput {
+    int pos;
+
+    public BytesReader(int pos) {
+      this.pos = pos;
+    }
+
+    @Override
+    public byte readByte() {
+      return bytes[pos--];
+    }
+
+    @Override
+    public void readBytes(byte[] b, int offset, int len) {
+      for(int i=0;i<len;i++) {
+        b[offset+i] = bytes[pos--];
+      }
+    }
+  }
+}