update ceph source to reef 18.1.2

[ceph.git] / ceph / src / jaegertracing / opentelemetry-cpp / sdk / src / common / fast_random_number_generator.h

diff --git a/ceph/src/jaegertracing/opentelemetry-cpp/sdk/src/common/fast_random_number_generator.h b/ceph/src/jaegertracing/opentelemetry-cpp/sdk/src/common/fast_random_number_generator.h
new file mode 100644 (file)
index 0000000..9887f2f
--- /dev/null
+++ b/ceph/src/jaegertracing/opentelemetry-cpp/sdk/src/common/fast_random_number_generator.h
@@ -0,0 +1,82 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+#pragma once
+
+#include <array>
+#include <cstdint>
+#include <limits>
+
+#include "opentelemetry/version.h"
+
+OPENTELEMETRY_BEGIN_NAMESPACE
+namespace sdk
+{
+namespace common
+{
+/**
+ * Profiling shows that random number generation can be a significant cost of
+ * span generation. This provides a faster random number generator than
+ * std::mt19937_64; and since we don't care about the other beneficial random
+ * number properties that std:mt19937_64 provides for this application, it's a
+ * entirely appropriate replacement.
+ *
+ * Note for Windows users - please make sure that NOMINMAX is defined, e.g.
+ *
+ * ...
+ * #define NOMINMAX
+ * #include <Windows.h>
+ * ...
+ *
+ * See:
+ * https://stackoverflow.com/questions/13416418/define-nominmax-using-stdmin-max
+ *
+ */
+class FastRandomNumberGenerator
+{
+public:
+  using result_type = uint64_t;
+
+  FastRandomNumberGenerator() noexcept = default;
+
+  template <class SeedSequence>
+  FastRandomNumberGenerator(SeedSequence &seed_sequence) noexcept
+  {
+    seed(seed_sequence);
+  }
+
+  uint64_t operator()() noexcept
+  {
+    // Uses the xorshift128p random number generation algorithm described in
+    // https://en.wikipedia.org/wiki/Xorshift
+    auto &state_a = state_[0];
+    auto &state_b = state_[1];
+    auto t        = state_a;
+    auto s        = state_b;
+    state_a       = s;
+    t ^= t << 23;        // a
+    t ^= t >> 17;        // b
+    t ^= s ^ (s >> 26);  // c
+    state_b = t;
+    return t + s;
+  }
+
+  // RandomNumberGenerator concept functions required from standard library.
+  // See http://www.cplusplus.com/reference/random/mt19937/
+  template <class SeedSequence>
+  void seed(SeedSequence &seed_sequence) noexcept
+  {
+    seed_sequence.generate(reinterpret_cast<uint32_t *>(state_.data()),
+                           reinterpret_cast<uint32_t *>(state_.data() + state_.size()));
+  }
+
+  static constexpr uint64_t min() noexcept { return 0; }
+
+  static constexpr uint64_t max() noexcept { return std::numeric_limits<uint64_t>::max(); }
+
+private:
+  std::array<uint64_t, 2> state_{};
+};
+}  // namespace common
+}  // namespace sdk
+OPENTELEMETRY_END_NAMESPACE