content: /*
   * Copyright (C) 2014 The Android Open Source Project
   *
   * 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 dexfuzz.program.mutators;
  
  import dexfuzz.Log;
  import dexfuzz.MutationStats;
  import dexfuzz.program.MInsn;
  import dexfuzz.program.MutatableCode;
  import dexfuzz.program.Mutation;
  import dexfuzz.rawdex.formats.ContainsConst;
  
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Random;
  
  public class ConstantValueChanger extends CodeMutator {
    /**
     * Every CodeMutator has an AssociatedMutation, representing the
     * mutation that this CodeMutator can perform, to allow separate
     * generateMutation() and applyMutation() phases, allowing serialization.
     */
    public static class AssociatedMutation extends Mutation {
      public int constInsnIdx;
      public long newConstant;
  
      @Override
      public String getString() {
        StringBuilder builder = new StringBuilder();
        builder.append(constInsnIdx).append(" ");
        builder.append(newConstant);
        return builder.toString();
      }
  
      @Override
      public void parseString(String[] elements) {
        constInsnIdx = Integer.parseInt(elements[2]);
        newConstant = Long.parseLong(elements[3]);
      }
    }
  
    // The following two methods are here for the benefit of MutationSerializer,
    // so it can create a CodeMutator and get the correct associated Mutation, as it
    // reads in mutations from a dump of mutations.
    @Override
    public Mutation getNewMutation() {
      return new AssociatedMutation();
    }
  
    public ConstantValueChanger() { }
  
    public ConstantValueChanger(Random rng, MutationStats stats, List<Mutation> mutations) {
      super(rng, stats, mutations);
      likelihood = 70;
    }
  
    // A cache that should only exist between generateMutation() and applyMutation(),
    // or be created at the start of applyMutation(), if we're reading in mutations from
    // a file.
    private List<MInsn> constInsns = null;
  
    private void generateCachedConstInsns(MutatableCode mutatableCode) {
      if (constInsns != null) {
        return;
      }
  
      constInsns = new ArrayList<MInsn>();
      for (MInsn mInsn : mutatableCode.getInstructions()) {
        if (mInsn.insn.info.format instanceof ContainsConst) {
          constInsns.add(mInsn);
        }
      }
    }
  
    @Override
    protected boolean canMutate(MutatableCode mutatableCode) {
      for (MInsn mInsn : mutatableCode.getInstructions()) {
        if (mInsn.insn.info.format instanceof ContainsConst) {
          return true;
        }
      }
  
      Log.debug("Method contains no const instructions.");
      return false;
    }
  
    @Override
    protected Mutation generateMutation(MutatableCode mutatableCode) {
      generateCachedConstInsns(mutatableCode);
  
      // Pick a random const instruction.
      int constInsnIdx = rng.nextInt(constInsns.size());
      MInsn constInsn = constInsns.get(constInsnIdx);
  
      // Get the constant.
      long oldConstant = ((ContainsConst)constInsn.insn.info.format).getConst(constInsn.insn);
  
      long newConstant = oldConstant;
  
      // Make a new constant.
      while (newConstant == oldConstant) {
        newConstant = rng.nextLong()
            % ((ContainsConst)constInsn.insn.info.format).getConstRange();
      }
  
      AssociatedMutation mutation = new AssociatedMutation();
      mutation.setup(this.getClass(), mutatableCode);
      mutation.constInsnIdx = constInsnIdx;
      mutation.newConstant = newConstant;
      return mutation;
    }
  
    @Override
    protected void applyMutation(Mutation uncastMutation) {
      // Cast the Mutation to our AssociatedMutation, so we can access its fields.
      AssociatedMutation mutation = (AssociatedMutation) uncastMutation;
      MutatableCode mutatableCode = mutation.mutatableCode;
  
      generateCachedConstInsns(mutatableCode);
  
      MInsn constInsn = constInsns.get(mutation.constInsnIdx);
  
      long oldConstant = ((ContainsConst)constInsn.insn.info.format).getConst(constInsn.insn);
  
      Log.info("Changed constant value #" + oldConstant + " to #" + mutation.newConstant
          + " in " + constInsn);
  
      stats.incrementStat("Changed constant value");
  
      // Set the new constant.
      ((ContainsConst)constInsn.insn.info.format).setConst(constInsn.insn, mutation.newConstant);
  
      // Clear cache.
      constInsns = null;
    }
  }
  