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 java.util.List;
  import java.util.Random;
  
  public class InstructionSwapper 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 swapInsnIdx;
      public int swapWithInsnIdx;
  
      @Override
      public String getString() {
        StringBuilder builder = new StringBuilder();
        builder.append(swapInsnIdx).append(" ");
        builder.append(swapWithInsnIdx);
        return builder.toString();
      }
  
      @Override
      public void parseString(String[] elements) {
        swapInsnIdx = Integer.parseInt(elements[2]);
        swapWithInsnIdx = Integer.parseInt(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 InstructionSwapper() { }
  
    public InstructionSwapper(Random rng, MutationStats stats, List<Mutation> mutations) {
      super(rng, stats, mutations);
      likelihood = 80;
    }
  
    @Override
    protected boolean canMutate(MutatableCode mutatableCode) {
      if (mutatableCode.getInstructionCount() == 1) {
        // Cannot swap one instruction.
        Log.debug("Cannot swap insns in a method with only one.");
        return false;
      }
      return true;
    }
  
    @Override
    protected Mutation generateMutation(MutatableCode mutatableCode) {
      int swapInsnIdx = 0;
      int swapWithInsnIdx = 0;
  
      boolean foundFirstInsn = false;
      boolean foundSecondInsn = false;
  
      while (!foundFirstInsn || !foundSecondInsn) {
        // Look for the first insn.
        while (!foundFirstInsn) {
          swapInsnIdx = rng.nextInt(mutatableCode.getInstructionCount());
          MInsn toBeSwapped = mutatableCode.getInstructionAt(swapInsnIdx);
          foundFirstInsn = true;
          if (toBeSwapped.insn.justRaw) {
            foundFirstInsn = false;
          }
        }
  
        // Look for the second insn.
        int secondInsnAttempts = 0;
        while (!foundSecondInsn) {
          int delta = rng.nextInt(5) - 1;
  
          if (delta == 0) {
            continue;
          }
  
          swapWithInsnIdx = swapInsnIdx + delta;
          foundSecondInsn = true;
  
          // Check insn is in valid range.
          if (swapWithInsnIdx < 0) {
            foundSecondInsn = false;
          } else if (swapWithInsnIdx >= mutatableCode.getInstructionCount()) {
            foundSecondInsn = false;
          }
  
          // Finally, check if we're swapping with a raw insn.
          if (foundSecondInsn) {
            if (mutatableCode.getInstructionAt(swapWithInsnIdx).insn.justRaw) {
              foundSecondInsn = false;
            }
          }
  
          // If we've checked 10 times for an insn to swap with,
          // and still found nothing, then try a new first insn.
          if (!foundSecondInsn) {
            secondInsnAttempts++;
            if (secondInsnAttempts == 10) {
              foundFirstInsn = false;
              break;
            }
          }
        }
      }
  
      AssociatedMutation mutation = new AssociatedMutation();
      mutation.setup(this.getClass(), mutatableCode);
      mutation.swapInsnIdx = swapInsnIdx;
      mutation.swapWithInsnIdx = swapWithInsnIdx;
      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;
  
      MInsn toBeSwapped = mutatableCode.getInstructionAt(mutation.swapInsnIdx);
      MInsn swappedWith = mutatableCode.getInstructionAt(mutation.swapWithInsnIdx);
  
      Log.info("Swapping " + toBeSwapped + " with " + swappedWith);
  
      stats.incrementStat("Swapped two instructions");
  
      mutatableCode.swapInstructionsByIndex(mutation.swapInsnIdx, mutation.swapWithInsnIdx);
  
      Log.info("Now " + swappedWith + " is swapped with " + toBeSwapped);
    }
  }
  