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+// Copyright 2019 The Amber Authors.
+//
+// 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.
+
+#include "samples/timestamp.h"
+
+#include <cassert>
+
+#if defined(_WIN32) || defined(_WIN64)
+#define SAMPLE_PLATFORM_WINDOWS 1
+#define SAMPLE_PLATFORM_POSIX 0
+#elif defined(__linux__) || defined(__APPLE__)
+#define SAMPLE_PLATFORM_POSIX 1
+#define SAMPLE_PLATFORM_WINDOWS 0
+#endif
+
+#if SAMPLE_PLATFORM_WINDOWS
+#include <windows.h>
+#elif SAMPLE_PLATFORM_POSIX
+#include <time.h>
+#else
+#error "Unknown platform"
+#endif
+
+namespace timestamp {
+
+uint64_t SampleGetTimestampNs() {
+  uint64_t timestamp = 0;
+
+#if SAMPLE_PLATFORM_WINDOWS
+
+  LARGE_INTEGER tick_per_seconds;
+  if (!QueryPerformanceFrequency(&tick_per_seconds)) {
+    return 0;
+  }
+  LARGE_INTEGER ticks;
+  if (!QueryPerformanceCounter(&ticks)) {
+    return 0;
+  }
+  double tick_duration_ns = static_cast<double>(1.0e9) /
+                            static_cast<double>(tick_per_seconds.QuadPart);
+  timestamp = uint64_t(static_cast<double>(ticks.QuadPart) * tick_duration_ns);
+
+#elif SAMPLE_PLATFORM_POSIX
+
+  struct timespec time;
+  if (clock_gettime(CLOCK_MONOTONIC, &time)) {
+    return 0;
+  }
+  timestamp = static_cast<uint64_t>((time.tv_sec * 1000000000) + time.tv_nsec);
+
+#else
+#error "Implement timestamp::SampleGetTimestampNs"
+#endif
+
+  return timestamp;
+}
+
+}  // namespace timestamp