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Rhino is an open-source implementation of JavaScript written entirely in Java. It is typically embedded into Java applications to provide scripting to end users.
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/* -*- Mode: java; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

package org.mozilla.classfile;

/**
 * A super block is defined as a contiguous chunk of code with a single entry
 * point and multiple exit points (therefore ending in an unconditional jump
 * or the end of the method). This is used to emulate OpenJDK's compiler, which
 * outputs stack map frames at the start of every super block except the method
 * start.
 */
final class SuperBlock {
  SuperBlock(int index, int start, int end, int[] initialLocals) {
    this.index = index;
    this.start = start;
    this.end = end;
    locals = new int[initialLocals.length];
    System.arraycopy(initialLocals, 0, locals, 0, initialLocals.length);
    stack = new int[0];
    isInitialized = false;
    isInQueue = false;
  }

  int getIndex() {
    return index;
  }

  int[] getLocals() {
    int[] copy = new int[locals.length];
    System.arraycopy(locals, 0, copy, 0, locals.length);
    return copy;
  }

  /**
   * Get a copy of the super block's locals without any trailing TOP types.
   *
   * This is useful for actual writing stack maps; during the computation of
   * stack map types, all local arrays have the same size; the max locals for
   * the method. In addition, DOUBLE and LONG types have trailing TOP types
   * because they occupy two words. For writing purposes, these are not
   * useful.
   */
  int[] getTrimmedLocals() {
    int last = locals.length - 1;
    // Exclude all of the trailing TOPs not bound to a DOUBLE/LONG
    while (last >= 0 && locals[last] == TypeInfo.TOP &&
        !TypeInfo.isTwoWords(locals[last - 1])) {
      last--;
    }
    last++;
    // Exclude trailing TOPs following a DOUBLE/LONG
    int size = last;
    for (int i = 0; i < last; i++) {
      if (TypeInfo.isTwoWords(locals[i])) {
        size--;
      }
    }
    int[] copy = new int[size];
    for (int i = 0, j = 0; i < size; i++, j++) {
      copy[i] = locals[j];
      if (TypeInfo.isTwoWords(locals[j])) {
        j++;
      }
    }
    return copy;
  }

  int[] getStack() {
    int[] copy = new int[stack.length];
    System.arraycopy(stack, 0, copy, 0, stack.length);
    return copy;
  }

  boolean merge(int[] locals, int localsTop, int[] stack, int stackTop,
      ConstantPool pool) {
    if (!isInitialized) {
      System.arraycopy(locals, 0, this.locals, 0, localsTop);
      this.stack = new int[stackTop];
      System.arraycopy(stack, 0, this.stack, 0, stackTop);
      isInitialized = true;
      return true;
    } else if (this.locals.length == localsTop &&
        this.stack.length == stackTop) {
      boolean localsChanged = mergeState(this.locals, locals, localsTop,
          pool);
      boolean stackChanged = mergeState(this.stack, stack, stackTop,
          pool);
      return localsChanged || stackChanged;
    } else {
      if (ClassFileWriter.StackMapTable.DEBUGSTACKMAP) {
        System.out.println("bad merge");
        System.out.println("current type state:");
        TypeInfo.print(this.locals, this.stack, pool);
        System.out.println("incoming type state:");
        TypeInfo.print(locals, localsTop, stack, stackTop, pool);
      }
      throw new IllegalArgumentException("bad merge attempt");
    }
  }

  /**
   * Merge an operand stack or local variable array with incoming state.
   *
   * They are treated the same way; by this point, it should already be
   * ensured that the array sizes are the same, which is the only additional
   * constraint that is imposed on merging operand stacks (the local variable
   * array is always the same size).
   */
  private static boolean mergeState(int[] current, int[] incoming, int size,
      ConstantPool pool) {
    boolean changed = false;
    for (int i = 0; i < size; i++) {
      int currentType = current[i];

      current[i] = TypeInfo.merge(current[i], incoming[i], pool);
      if (currentType != current[i]) {
        changed = true;
      }
    }
    return changed;
  }

  int getStart() {
    return start;
  }

  int getEnd() {
    return end;
  }

  @Override
  public String toString() {
    return "sb " + index;
  }

  boolean isInitialized() {
    return isInitialized;
  }

  void setInitialized(boolean b) {
    isInitialized = b;
  }

  boolean isInQueue() {
    return isInQueue;
  }

  void setInQueue(boolean b) {
    isInQueue = b;
  }

  private int index;
  private int start;
  private int end;
  private int[] locals;
  private int[] stack;
  private boolean isInitialized;
  private boolean isInQueue;
}