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      1 //===- FuzzerCrossOver.cpp - Cross over two test inputs -------------------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 // Cross over test inputs.
     10 //===----------------------------------------------------------------------===//
     11 
     12 #include "FuzzerDefs.h"
     13 #include "FuzzerMutate.h"
     14 #include "FuzzerRandom.h"
     15 #include <cstring>
     16 
     17 namespace fuzzer {
     18 
     19 // Cross Data1 and Data2, store the result (up to MaxOutSize bytes) in Out.
     20 size_t MutationDispatcher::CrossOver(const uint8_t *Data1, size_t Size1,
     21                                      const uint8_t *Data2, size_t Size2,
     22                                      uint8_t *Out, size_t MaxOutSize) {
     23   assert(Size1 || Size2);
     24   MaxOutSize = Rand(MaxOutSize) + 1;
     25   size_t OutPos = 0;
     26   size_t Pos1 = 0;
     27   size_t Pos2 = 0;
     28   size_t *InPos = &Pos1;
     29   size_t InSize = Size1;
     30   const uint8_t *Data = Data1;
     31   bool CurrentlyUsingFirstData = true;
     32   while (OutPos < MaxOutSize && (Pos1 < Size1 || Pos2 < Size2)) {
     33     // Merge a part of Data into Out.
     34     size_t OutSizeLeft = MaxOutSize - OutPos;
     35     if (*InPos < InSize) {
     36       size_t InSizeLeft = InSize - *InPos;
     37       size_t MaxExtraSize = std::min(OutSizeLeft, InSizeLeft);
     38       size_t ExtraSize = Rand(MaxExtraSize) + 1;
     39       memcpy(Out + OutPos, Data + *InPos, ExtraSize);
     40       OutPos += ExtraSize;
     41       (*InPos) += ExtraSize;
     42     }
     43     // Use the other input data on the next iteration.
     44     InPos  = CurrentlyUsingFirstData ? &Pos2 : &Pos1;
     45     InSize = CurrentlyUsingFirstData ? Size2 : Size1;
     46     Data   = CurrentlyUsingFirstData ? Data2 : Data1;
     47     CurrentlyUsingFirstData = !CurrentlyUsingFirstData;
     48   }
     49   return OutPos;
     50 }
     51 
     52 }  // namespace fuzzer
     53