Properly handle supported types in std::uniform_int_distribution.

Fixes #209.

test/test_utils.hpp

@@ -125,6 +125,22 @@ inline __half operator-(__half const& lhs, __half const& rhs) {
 
 #endif // defined(AL_HAS_ROCM) && defined(AL_HAS_NCCL)
 
+// It turns out that, per the C++ standard, std::uniform_int_distribution
+// is only defined for a subset of integer types, and using an unsupported
+// type is undefined behavior. In libstdc++, everything seems to just
+// work, but libc++ throws a compile error. This works around that.
+namespace internal {
+template <typename T> struct IsRngIntType : std::false_type {};
+template <> struct IsRngIntType<short> : std::true_type {};
+template <> struct IsRngIntType<unsigned short> : std::true_type {};
+template <> struct IsRngIntType<int> : std::true_type {};
+template <> struct IsRngIntType<unsigned int> : std::true_type {};
+template <> struct IsRngIntType<long> : std::true_type {};
+template <> struct IsRngIntType<unsigned long> : std::true_type {};
+template <> struct IsRngIntType<long long> : std::true_type {};
+template <> struct IsRngIntType<unsigned long long> : std::true_type {};
+}
+
 /** Helper for generating random data. */
 template <typename T, typename Generator,
           std::enable_if_t<std::is_floating_point<T>::value, bool> = true>
@@ -133,11 +149,30 @@ T gen_random_val(Generator& g) {
   return rng(g);
 }
 template <typename T, typename Generator,
-          std::enable_if_t<std::is_integral<T>::value, bool> = true>
+          std::enable_if_t<std::is_integral<T>::value
+                           && internal::IsRngIntType<T>::value, bool> = true>
 T gen_random_val(Generator& g) {
   std::uniform_int_distribution<T> rng;
   return rng(g);
 }
+template <typename T, typename Generator,
+          std::enable_if_t<std::is_integral<T>::value
+                           && !internal::IsRngIntType<T>::value
+                           && std::is_signed<T>::value, bool> = true>
+T gen_random_val(Generator& g) {
+  static_assert(sizeof(T) <= sizeof(short), "Type too large");
+  std::uniform_int_distribution<short> rng;
+  return static_cast<T>(rng(g));
+}
+template <typename T, typename Generator,
+          std::enable_if_t<std::is_integral<T>::value
+                           && !internal::IsRngIntType<T>::value
+                           && std::is_unsigned<T>::value, bool> = true>
+T gen_random_val(Generator& g) {
+  static_assert(sizeof(T) <= sizeof(short), "Type too large");
+  std::uniform_int_distribution<short> rng;
+  return static_cast<T>(rng(g));
+}
 
 /** Helper for generating random vectors. */
 template <typename T>