1 files changed, 89 insertions, 1 deletions

diff --git a/src/tools/fuzzing/random.h b/src/tools/fuzzing/random.h
index 156f248ca..845aa2fa5 100644
--- a/src/tools/fuzzing/random.h
+++ b/src/tools/fuzzing/random.h
@@ -18,8 +18,11 @@
 #define wasm_tools_fuzzing_random_h
 
 #include <cstdint>
+#include <map>
 #include <vector>
 
+#include "wasm-features.h"
+
 namespace wasm {
 
 class Random {
@@ -33,9 +36,13 @@ class Random {
   // After we finish the input, we start going through it again, but xoring
   // so it's not identical.
   int xorFactor = 0;
+  // Features used for picking among FeatureOptions.
+  FeatureSet features;
 
 public:
-  Random(std::vector<char>&& bytes);
+  Random(std::vector<char>&& bytes, FeatureSet features);
+  Random(std::vector<char>&& bytes)
+    : Random(std::move(bytes), FeatureSet::All) {}
 
   // Methods for getting random data.
   int8_t get();
@@ -55,6 +62,87 @@ public:
   uint32_t upToSquared(uint32_t x) { return upTo(upTo(x)); }
 
   bool finished() { return finishedInput; }
+
+  // Pick from a vector-like container
+  template<typename T> const typename T::value_type& pick(const T& vec) {
+    assert(!vec.empty());
+    auto index = upTo(vec.size());
+    return vec[index];
+  }
+
+  // Pick from a fixed list
+  template<typename T, typename... Args> T pick(T first, Args... args) {
+    auto num = sizeof...(Args) + 1;
+    auto temp = upTo(num);
+    return pickGivenNum<T>(temp, first, args...);
+  }
+
+  template<typename T> T pickGivenNum(size_t num, T first) {
+    assert(num == 0);
+    return first;
+  }
+
+// Trick to avoid a bug in GCC 7.x.
+// Upstream bug report: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82800
+#define GCC_VERSION                                                            \
+  (__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__)
+#if GCC_VERSION > 70000 && GCC_VERSION < 70300
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
+#endif
+
+  template<typename T, typename... Args>
+  T pickGivenNum(size_t num, T first, Args... args) {
+    if (num == 0) {
+      return first;
+    }
+    return pickGivenNum<T>(num - 1, args...);
+  }
+
+#if GCC_VERSION > 70000 && GCC_VERSION < 70300
+#pragma GCC diagnostic pop
+#endif
+
+  template<typename T> struct FeatureOptions {
+    template<typename... Ts>
+    FeatureOptions<T>& add(FeatureSet feature, T option, Ts... rest) {
+      options[feature].push_back(option);
+      return add(feature, rest...);
+    }
+
+    struct WeightedOption {
+      T option;
+      size_t weight;
+    };
+
+    template<typename... Ts>
+    FeatureOptions<T>&
+    add(FeatureSet feature, WeightedOption weightedOption, Ts... rest) {
+      for (size_t i = 0; i < weightedOption.weight; i++) {
+        options[feature].push_back(weightedOption.option);
+      }
+      return add(feature, rest...);
+    }
+
+    FeatureOptions<T>& add(FeatureSet feature) { return *this; }
+
+    std::map<FeatureSet, std::vector<T>> options;
+  };
+
+  template<typename T> std::vector<T> items(FeatureOptions<T>& picker) {
+    std::vector<T> matches;
+    for (const auto& item : picker.options) {
+      if (features.has(item.first)) {
+        matches.reserve(matches.size() + item.second.size());
+        matches.insert(matches.end(), item.second.begin(), item.second.end());
+      }
+    }
+    return matches;
+  }
+
+  template<typename T> const T pick(FeatureOptions<T>& picker) {
+    return pick(items(picker));
+  }
 };
 
 } // namespace wasm