add libfuzzer custom mutator, minor enhancements and fixes

custom_mutators/libfuzzer/FuzzerRandom.h

@@ -0,0 +1,38 @@
+//===- FuzzerRandom.h - Internal header for the Fuzzer ----------*- C++ -* ===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+// fuzzer::Random
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_FUZZER_RANDOM_H
+#define LLVM_FUZZER_RANDOM_H
+
+#include <random>
+
+namespace fuzzer {
+class Random : public std::minstd_rand {
+ public:
+  Random(unsigned int seed) : std::minstd_rand(seed) {}
+  result_type operator()() { return this->std::minstd_rand::operator()(); }
+  size_t Rand() { return this->operator()(); }
+  size_t RandBool() { return Rand() % 2; }
+  size_t SkewTowardsLast(size_t n) {
+    size_t T = this->operator()(n * n);
+    size_t Res = sqrt(T);
+    return Res;
+  }
+  size_t operator()(size_t n) { return n ? Rand() % n : 0; }
+  intptr_t operator()(intptr_t From, intptr_t To) {
+    assert(From < To);
+    intptr_t RangeSize = To - From + 1;
+    return operator()(RangeSize) + From;
+  }
+};
+
+}  // namespace fuzzer
+
+#endif  // LLVM_FUZZER_RANDOM_H