Add samplingTime mode to nanobench

tools/timer/SysTimer_windows.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include "SysTimer_windows.h"
 
 #include <intrin.h>
 
@@ skipping 20 matching lines @@
 
 double SysTimer::endCpu() {
     ULONGLONG end_cpu = win_cpu_time();
     return static_cast<double>(end_cpu - fStartCpu) / 10000.0L;
 }
 
 // On recent Intel chips (roughly, "has Core or Atom in its name") __rdtsc will always tick
 // at the CPU's maximum rate, even while power management clocks the CPU up and down.
 // That's great, because it makes measuring wall time super simple.
 
+static double ticks_to_ms(unsigned _int64 ticks) {
+    // This seems to, weirdly, give the CPU frequency in kHz.  That's exactly what we want!
+    LARGE_INTEGER freq_khz;
+    QueryPerformanceFrequency(&freq_khz);
+
+    return static_cast<double>(ticks) / static_cast<double>(freq_khz.QuadPart);
+}
+
 void SysTimer::startWall() {
     fStartWall = __rdtsc();
 }
 
 double SysTimer::endWall() {
     unsigned __int64 end = __rdtsc();
+    return ticks_to_ms(end - fStartWall);
+}
 
-    // This seems to, weirdly, give the CPU frequency in kHz.  That's exactly what we want!
-    LARGE_INTEGER freq_khz;
-    QueryPerformanceFrequency(&freq_khz);
-
-    return static_cast<double>(end - fStartWall) / static_cast<double>(freq_khz.QuadPart);
+double GetTimeMs() {
+    static const unsigned __int64 launchTime = __rdtsc();
+    return ticks_to_ms(__rdtsc() - launchTime);
 }