SkTime::GetNSecs()

src/core/SkTime.cpp

Index: src/core/SkTime.cpp
diff --git a/src/core/SkTime.cpp b/src/core/SkTime.cpp
index fa6c04447de0ade9f8bfaf927151215d6eec85ec..86a0685c70af27703490024f15bf80ff5aef5152 100644
--- a/src/core/SkTime.cpp
+++ b/src/core/SkTime.cpp
@@ -5,6 +5,7 @@
  * found in the LICENSE file.
  */
 
+#include "SkOncePtr.h"
 #include "SkString.h"
 #include "SkTime.h"
 
@@ -22,3 +23,38 @@ void SkTime::DateTime::toISO8601(SkString* dst) const {
                     timeZoneMinutes);
     }
 }
+
+#if defined(_MSC_VER)
+    // TODO: try std::chrono again with MSVC 2015?
+    #include <intrin.h>
+    SK_DECLARE_STATIC_ONCE_PTR(double, ns_per_tick);
+    double SkTime::GetNSecs() {
+        uint64_t ticks = __rdtsc();
+        return ticks * *ns_per_tick.get([]{
+            LARGE_INTEGER khz;  // The docs say this returns Hz, but it returns KHz.
+            QueryPerformanceFrequency(&khz);
+            return new double(1e6 / khz.QuadPart);
+        });
+    }
+#elif defined(__MACH__)
+    // TODO: fold into std::chrono when available?
+    #include <mach/mach_time.h>
+    SK_DECLARE_STATIC_ONCE_PTR(double, ns_per_tick);
+    double SkTime::GetNSecs() {
+        uint64_t ticks = mach_absolute_time();
+        return ticks * *ns_per_tick.get([]{
+            mach_timebase_info_data_t timebase;
+            (void)mach_timebase_info(&timebase);
+            return new double(timebase.numer * 1.0 / timebase.denom);
+        });
+    }
+#else
+    // This std::chrono code looks great on Linux and Android,
+    // but MSVC 2013 returned mostly garbage (0ns times, etc).
+    #include <chrono>
+    double SkTime::GetNSecs() {
+        auto now = std::chrono::high_resolution_clock::now();
+        std::chrono::duration<double, std::nano> ns = now.time_since_epoch();
+        return ns.count();
+    }
+#endif