From 005cd3b630fcf0f3870f426a0db5e54400a59ef9 Mon Sep 17 00:00:00 2001
From: Johannes Stoelp <johannes.stoelp@gmail.com>
Date: Mon, 3 Jul 2023 22:17:34 +0200
Subject: timer: add simple linux watchclock timer

---
 Makefile      |  1 +
 test/timer.cc | 28 ++++++++++++++++++++++++++++
 timer.h       | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 81 insertions(+)
 create mode 100644 test/timer.cc
 create mode 100644 timer.h

diff --git a/Makefile b/Makefile
index 97ca475..ceaa80e 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,6 @@
 TEST += bitfield
 TEST += option
+TEST += timer
 
 # -- INTERNALS -----------------------------------------------------------------
 
diff --git a/test/timer.cc b/test/timer.cc
new file mode 100644
index 0000000..078c4bb
--- /dev/null
+++ b/test/timer.cc
@@ -0,0 +1,28 @@
+#include <timer.h>
+#include <unistd.h>
+#include <cstdio>
+
+int main() {
+  timer::timer T;
+
+  const auto show_time = [&T]() {
+    std::fprintf(stderr, "usec=%f msec=%f sec=%f\n", T.as_usec(), T.as_msec(),
+                 T.as_sec());
+  };
+
+  {
+    puts("Sleep 100ms");
+    timer::scoped_timer s{T};
+    usleep(100 * 1000);
+  }
+  show_time();
+
+  {
+    puts("Sleep 500ms");
+    timer::scoped_timer s{T};
+    usleep(500 * 1000);
+  }
+  show_time();
+
+  return 0;
+}
diff --git a/timer.h b/timer.h
new file mode 100644
index 0000000..933c02c
--- /dev/null
+++ b/timer.h
@@ -0,0 +1,52 @@
+#include <cstdint>
+#include <ctime>
+
+namespace timer {
+struct timer {
+  constexpr timer() = default;
+
+  void start() {
+    clock_gettime(kClock, &m_start);
+  }
+
+  void stop() {
+    timespec end;
+    clock_gettime(kClock, &end);
+
+    m_nanos += ((end.tv_sec - m_start.tv_sec) * 1000000000ull) +
+               (end.tv_nsec - m_start.tv_nsec);
+  }
+
+  constexpr double as_sec() const {
+    return as_msec() / 1000.0;
+  }
+
+  constexpr double as_msec() const {
+    return as_usec() / 1000.0;
+  }
+
+  constexpr double as_usec() const {
+    return static_cast<double>(m_nanos) / 1000.0;
+  }
+
+ private:
+  static constexpr clockid_t kClock = CLOCK_MONOTONIC_RAW;
+
+  timespec m_start{};
+  std::uint64_t m_nanos{0};
+};
+
+struct scoped_timer {
+  explicit scoped_timer(timer& t) : m_timer(t) {
+    m_timer.start();
+  }
+
+  ~scoped_timer() {
+    m_timer.stop();
+  }
+
+ private:
+  timer& m_timer;
+};
+
+}  // namespace timer
-- 
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