Index: compiler-rt/lib/fuzzer/FuzzerDriver.cpp
===================================================================
--- compiler-rt/lib/fuzzer/FuzzerDriver.cpp
+++ compiler-rt/lib/fuzzer/FuzzerDriver.cpp
@@ -867,7 +867,7 @@
   }
 
   if (Flags.fork)
-    FuzzWithFork(F->GetMD().GetRand(), Options, Args, *Inputs, Flags.fork);
+    FuzzWithFork(F->GetMD().GetRand(), Options, Args, *Inputs, Flags.fork, Flags.NumCorpuses);
 
   if (Flags.merge)
     Merge(F, Options, Args, *Inputs, Flags.merge_control_file);
Index: compiler-rt/lib/fuzzer/FuzzerFlags.def
===================================================================
--- compiler-rt/lib/fuzzer/FuzzerFlags.def
+++ compiler-rt/lib/fuzzer/FuzzerFlags.def
@@ -56,6 +56,7 @@
 FUZZER_FLAG_INT(max_total_time, 0, "If positive, indicates the maximal total "
                                    "time in seconds to run the fuzzer.")
 FUZZER_FLAG_INT(help, 0, "Print help.")
+FUZZER_FLAG_INT(NumCorpuses, 1, "FOR fork mode. Divide the main corpus into N parts according to size.")
 FUZZER_FLAG_INT(fork, 0, "Experimental mode where fuzzing happens "
                 "in a subprocess")
 FUZZER_FLAG_INT(ignore_timeouts, 1, "Ignore timeouts in fork mode")
Index: compiler-rt/lib/fuzzer/FuzzerFork.h
===================================================================
--- compiler-rt/lib/fuzzer/FuzzerFork.h
+++ compiler-rt/lib/fuzzer/FuzzerFork.h
@@ -18,7 +18,7 @@
 namespace fuzzer {
 void FuzzWithFork(Random &Rand, const FuzzingOptions &Options,
                   const Vector<std::string> &Args,
-                  const Vector<std::string> &CorpusDirs, int NumJobs);
+                  const Vector<std::string> &CorpusDirs, int NumJobs, int NumCorpuses);
 } // namespace fuzzer
 
 #endif // LLVM_FUZZER_FORK_H
Index: compiler-rt/lib/fuzzer/FuzzerFork.cpp
===================================================================
--- compiler-rt/lib/fuzzer/FuzzerFork.cpp
+++ compiler-rt/lib/fuzzer/FuzzerFork.cpp
@@ -95,6 +95,7 @@
   Set<uint32_t> Features, Cov;
   Set<std::string> FilesWithDFT;
   Vector<std::string> Files;
+  Vector<std::size_t> FilesSizes;
   Random *Rand;
   std::chrono::system_clock::time_point ProcessStartTime;
   int Verbosity = 0;
@@ -114,7 +115,7 @@
         .count();
   }
 
-  FuzzJob *CreateNewJob(size_t JobId) {
+  FuzzJob *CreateNewJob(size_t JobId, int NumCorpuses) {
     Command Cmd(Args);
     Cmd.removeFlag("fork");
     Cmd.removeFlag("runs");
@@ -135,11 +136,26 @@
     std::string Seeds;
     if (size_t CorpusSubsetSize =
             std::min(Files.size(), (size_t)sqrt(Files.size() + 2))) {
+      size_t AverageSize = Files.size() / NumCorpuses + 1;
       auto Time1 = std::chrono::system_clock::now();
+      size_t StartIndex = ( (JobId-1) % NumCorpuses ) *  AverageSize;
       for (size_t i = 0; i < CorpusSubsetSize; i++) {
-        auto &SF = Files[Rand->SkewTowardsLast(Files.size())];
-        Seeds += (Seeds.empty() ? "" : ",") + SF;
-        CollectDFT(SF);
+        //size_t j = Rand->SkewTowardsLast(AverageSize);
+        std::random_device rd; 
+	std::mt19937 randomseed(rd()); 
+	std::uniform_int_distribution<> rand(0,AverageSize);
+	size_t j = rand(randomseed);
+        size_t m = j + StartIndex;
+        if (m < Files.size()) {
+                auto &SF = Files[m];
+		Seeds += (Seeds.empty() ? "" : ",") + SF;
+		CollectDFT(SF);
+        }
+        else  {
+                auto &SF = Files[rand(randomseed)];
+		Seeds += (Seeds.empty() ? "" : ",") + SF;
+		CollectDFT(SF);
+        }
       }
       auto Time2 = std::chrono::system_clock::now();
       auto DftTimeInSeconds = duration_cast<seconds>(Time2 - Time1).count();
@@ -179,7 +195,7 @@
     return Job;
   }
 
-  void RunOneMergeJob(FuzzJob *Job) {
+  void RunOneMergeJob(FuzzJob *Job, int NumCorpuses) {
     auto Stats = ParseFinalStatsFromLog(Job->LogPath);
     NumRuns += Stats.number_of_executed_units;
 
@@ -219,7 +235,10 @@
       auto U = FileToVector(Path);
       auto NewPath = DirPlusFile(MainCorpusDir, Hash(U));
       WriteToFile(U, NewPath);
-      Files.push_back(NewPath);
+      long usz = U.size();
+      auto idx = std::upper_bound(FilesSizes.begin(), FilesSizes.end(), usz) - FilesSizes.begin(); 
+      FilesSizes.insert(FilesSizes.begin() + idx, usz);
+      Files.insert(Files.begin() + idx, NewPath);
     }
     Features.insert(NewFeatures.begin(), NewFeatures.end());
     Cov.insert(NewCov.begin(), NewCov.end());
@@ -284,7 +303,7 @@
 // This is just a skeleton of an experimental -fork=1 feature.
 void FuzzWithFork(Random &Rand, const FuzzingOptions &Options,
                   const Vector<std::string> &Args,
-                  const Vector<std::string> &CorpusDirs, int NumJobs) {
+                  const Vector<std::string> &CorpusDirs, int NumJobs, int NumCorpuses) {
   Printf("INFO: -fork=%d: fuzzing in separate process(s)\n", NumJobs);
 
   GlobalEnv Env;
@@ -312,8 +331,10 @@
     Env.MainCorpusDir = CorpusDirs[0];
 
   if (Options.KeepSeed) {
-    for (auto &File : SeedFiles)
+    for (auto &File : SeedFiles){
       Env.Files.push_back(File.File);
+      Env.FilesSizes.push_back(File.Size);
+    }
   } else {
     auto CFPath = DirPlusFile(Env.TempDir, "merge.txt");
     Set<uint32_t> NewFeatures, NewCov;
@@ -323,9 +344,15 @@
     Env.Cov.insert(NewFeatures.begin(), NewFeatures.end());
     RemoveFile(CFPath);
   }
+
+  for (auto &path : Env.Files) {
+	Env.FilesSizes.push_back(FileSize(path));
+  }
+
   Printf("INFO: -fork=%d: %zd seed inputs, starting to fuzz in %s\n", NumJobs,
          Env.Files.size(), Env.TempDir.c_str());
 
+
   int ExitCode = 0;
 
   JobQueue FuzzQ, MergeQ;
@@ -341,7 +368,7 @@
   Vector<std::thread> Threads;
   for (int t = 0; t < NumJobs; t++) {
     Threads.push_back(std::thread(WorkerThread, &FuzzQ, &MergeQ));
-    FuzzQ.Push(Env.CreateNewJob(JobId++));
+    FuzzQ.Push(Env.CreateNewJob(JobId++, NumCorpuses));
   }
 
   while (true) {
@@ -356,7 +383,7 @@
     }
     Fuzzer::MaybeExitGracefully();
 
-    Env.RunOneMergeJob(Job.get());
+    Env.RunOneMergeJob(Job.get(), NumCorpuses);
 
     // Continue if our crash is one of the ignorred ones.
     if (Options.IgnoreTimeouts && ExitCode == Options.TimeoutExitCode)
@@ -398,10 +425,25 @@
       StopJobs();
       break;
     }
-
-    FuzzQ.Push(Env.CreateNewJob(JobId++));
+    if (Env.Files.size() >= 1 && Env.Files.size() < 1600 )
+	    NumCorpuses = 16;
+    if (Env.Files.size() >= 1600 && Env.Files.size() < 3600 )
+	    NumCorpuses = 20;
+    if (Env.Files.size() >= 3600 && Env.Files.size() < 6400 )
+	    NumCorpuses = 24;
+    if (Env.Files.size() >= 6400 && Env.Files.size() < 8100 )
+	    NumCorpuses = 32;
+    if (Env.Files.size() >= 8100 && Env.Files.size() < 12000 )
+	    NumCorpuses = 36;
+    if (Env.Files.size() >= 12000 && Env.Files.size() < 16000 )
+	    NumCorpuses = 40;
+    if (Env.Files.size() >= 16000 && Env.Files.size() < 30000 )
+	    NumCorpuses = 60;
+    if(Env.Files.size() >= 30000)
+	    NumCorpuses = 80;
+
+    FuzzQ.Push(Env.CreateNewJob(JobId++, NumCorpuses));
   }
-
   for (auto &T : Threads)
     T.join();