vendor/llvm/llvm-trunk-r321017

1 files changed, 97 insertions, 0 deletions

diff --git a/include/llvm/FuzzMutate/Random.h b/include/llvm/FuzzMutate/Random.h
new file mode 100644
index 000000000000..3a5f46a07554
--- /dev/null
+++ b/include/llvm/FuzzMutate/Random.h
@@ -0,0 +1,97 @@
+//===--- Random.h - Utilities for random sampling -------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Utilities for random sampling.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_FUZZMUTATE_RANDOM_H
+#define LLVM_FUZZMUTATE_RANDOM_H
+
+#include <random>
+#include "llvm/Support/raw_ostream.h"
+namespace llvm {
+
+/// Return a uniformly distributed random value between \c Min and \c Max
+template <typename T, typename GenT> T uniform(GenT &Gen, T Min, T Max) {
+  return std::uniform_int_distribution<T>(Min, Max)(Gen);
+}
+
+/// Return a uniformly distributed random value of type \c T
+template <typename T, typename GenT> T uniform(GenT &Gen) {
+  return uniform<T>(Gen, std::numeric_limits<T>::min(),
+                    std::numeric_limits<T>::max());
+}
+
+/// Randomly selects an item by sampling into a set with an unknown number of
+/// elements, which may each be weighted to be more likely choices.
+template <typename T, typename GenT> class ReservoirSampler {
+  GenT &RandGen;
+  typename std::remove_const<T>::type Selection = {};
+  uint64_t TotalWeight = 0;
+
+public:
+  ReservoirSampler(GenT &RandGen) : RandGen(RandGen) {}
+
+  uint64_t totalWeight() const { return TotalWeight; }
+  bool isEmpty() const { return TotalWeight == 0; }
+
+  const T &getSelection() const {
+    assert(!isEmpty() && "Nothing selected");
+    return Selection;
+  }
+
+  explicit operator bool() const { return !isEmpty();}
+  const T &operator*() const { return getSelection(); }
+
+  /// Sample each item in \c Items with unit weight
+  template <typename RangeT> ReservoirSampler &sample(RangeT &&Items) {
+    for (auto &I : Items)
+      sample(I, 1);
+    return *this;
+  }
+
+  /// Sample a single item with the given weight.
+  ReservoirSampler &sample(const T &Item, uint64_t Weight) {
+    if (!Weight)
+      // If the weight is zero, do nothing.
+      return *this;
+    TotalWeight += Weight;
+    // Consider switching from the current element to this one.
+    if (uniform<uint64_t>(RandGen, 1, TotalWeight) <= Weight)
+      Selection = Item;
+    return *this;
+  }
+};
+
+template <typename GenT, typename RangeT,
+          typename ElT = typename std::remove_reference<
+              decltype(*std::begin(std::declval<RangeT>()))>::type>
+ReservoirSampler<ElT, GenT> makeSampler(GenT &RandGen, RangeT &&Items) {
+  ReservoirSampler<ElT, GenT> RS(RandGen);
+  RS.sample(Items);
+  return RS;
+}
+
+template <typename GenT, typename T>
+ReservoirSampler<T, GenT> makeSampler(GenT &RandGen, const T &Item,
+                                      uint64_t Weight) {
+  ReservoirSampler<T, GenT> RS(RandGen);
+  RS.sample(Item, Weight);
+  return RS;
+}
+
+template <typename T, typename GenT>
+ReservoirSampler<T, GenT> makeSampler(GenT &RandGen) {
+  return ReservoirSampler<T, GenT>(RandGen);
+}
+
+} // End llvm namespace
+
+#endif // LLVM_FUZZMUTATE_RANDOM_H