Backport ceil, floor, round from C++17 std::chrono

[folly.git] / folly / Chrono.h

diff --git a/folly/Chrono.h b/folly/Chrono.h
new file mode 100644 (file)
index 0000000..852a74b
--- /dev/null
+++ b/folly/Chrono.h
@@ -0,0 +1,154 @@
+/*
+ * Copyright 2017 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <chrono>
+#include <type_traits>
+
+/***
+ *  include or backport:
+ *  * std::chrono::ceil
+ *  * std::chrono::floor
+ *  * std::chrono::round
+ */
+
+#if __cpp_lib_chrono >= 201510 || _MSC_VER
+
+namespace folly {
+namespace chrono {
+
+/* using override */ using std::chrono::ceil;
+/* using override */ using std::chrono::floor;
+/* using override */ using std::chrono::round;
+}
+}
+
+#else
+
+namespace folly {
+namespace chrono {
+
+namespace detail {
+
+//  from: http://en.cppreference.com/w/cpp/chrono/duration/ceil, CC-BY-SA
+template <typename T>
+struct is_duration : std::false_type {};
+template <typename Rep, typename Period>
+struct is_duration<std::chrono::duration<Rep, Period>> : std::true_type {};
+
+template <typename To, typename Duration>
+constexpr To ceil_impl(Duration const& d, To const& t) {
+  return t < d ? t + To{1} : t;
+}
+
+template <typename To, typename Duration>
+constexpr To floor_impl(Duration const& d, To const& t) {
+  return t > d ? t - To{1} : t;
+}
+
+template <typename To, typename Diff>
+constexpr To round_impl(To const& t0, To const& t1, Diff diff0, Diff diff1) {
+  return diff0 < diff1 ? t0 : diff1 < diff0 ? t1 : t0.count() & 1 ? t1 : t0;
+}
+
+template <typename To, typename Duration>
+constexpr To round_impl(Duration const& d, To const& t0, To const& t1) {
+  return round_impl(t0, t1, d - t0, t1 - d);
+}
+
+template <typename To, typename Duration>
+constexpr To round_impl(Duration const& d, To const& t0) {
+  return round_impl(d, t0, t0 + To{1});
+}
+}
+
+//  mimic: std::chrono::ceil, C++17
+//  from: http://en.cppreference.com/w/cpp/chrono/duration/ceil, CC-BY-SA
+template <
+    typename To,
+    typename Rep,
+    typename Period,
+    typename = typename std::enable_if<detail::is_duration<To>::value>::type>
+constexpr To ceil(std::chrono::duration<Rep, Period> const& d) {
+  return detail::ceil_impl(d, std::chrono::duration_cast<To>(d));
+}
+
+//  mimic: std::chrono::ceil, C++17
+//  from: http://en.cppreference.com/w/cpp/chrono/time_point/ceil, CC-BY-SA
+template <
+    typename To,
+    typename Clock,
+    typename Duration,
+    typename = typename std::enable_if<detail::is_duration<To>::value>::type>
+constexpr std::chrono::time_point<Clock, To> ceil(
+    std::chrono::time_point<Clock, Duration> const& tp) {
+  return std::chrono::time_point<Clock, To>{ceil<To>(tp.time_since_epoch())};
+}
+
+//  mimic: std::chrono::floor, C++17
+//  from: http://en.cppreference.com/w/cpp/chrono/duration/floor, CC-BY-SA
+template <
+    typename To,
+    typename Rep,
+    typename Period,
+    typename = typename std::enable_if<detail::is_duration<To>::value>::type>
+constexpr To floor(std::chrono::duration<Rep, Period> const& d) {
+  return detail::floor_impl(d, std::chrono::duration_cast<To>(d));
+}
+
+//  mimic: std::chrono::floor, C++17
+//  from: http://en.cppreference.com/w/cpp/chrono/time_point/floor, CC-BY-SA
+template <
+    typename To,
+    typename Clock,
+    typename Duration,
+    typename = typename std::enable_if<detail::is_duration<To>::value>::type>
+constexpr std::chrono::time_point<Clock, To> floor(
+    std::chrono::time_point<Clock, Duration> const& tp) {
+  return std::chrono::time_point<Clock, To>{floor<To>(tp.time_since_epoch())};
+}
+
+//  mimic: std::chrono::round, C++17
+//  from: http://en.cppreference.com/w/cpp/chrono/duration/round, CC-BY-SA
+template <
+    typename To,
+    typename Rep,
+    typename Period,
+    typename = typename std::enable_if<
+        detail::is_duration<To>::value &&
+        !std::chrono::treat_as_floating_point<typename To::rep>::value>::type>
+constexpr To round(std::chrono::duration<Rep, Period> const& d) {
+  return detail::round_impl(d, floor<To>(d));
+}
+
+//  mimic: std::chrono::round, C++17
+//  from: http://en.cppreference.com/w/cpp/chrono/time_point/round, CC-BY-SA
+template <
+    typename To,
+    typename Clock,
+    typename Duration,
+    typename = typename std::enable_if<
+        detail::is_duration<To>::value &&
+        !std::chrono::treat_as_floating_point<typename To::rep>::value>::type>
+constexpr std::chrono::time_point<Clock, To> round(
+    std::chrono::time_point<Clock, Duration> const& tp) {
+  return std::chrono::time_point<Clock, To>{round<To>(tp.time_since_epoch())};
+}
+}
+}
+
+#endif