Add samplingTime mode to nanobench

tools/timer/SysTimer_mach.cpp

Index: tools/timer/SysTimer_mach.cpp
diff --git a/tools/timer/SysTimer_mach.cpp b/tools/timer/SysTimer_mach.cpp
index aca12dee5203afb2109aa47d6d7b8a23c183e129..9716988a04284d75f89fc51dd56dc63858fe9d56 100644
--- a/tools/timer/SysTimer_mach.cpp
+++ b/tools/timer/SysTimer_mach.cpp
@@ -39,6 +39,16 @@ static double interval_in_ms(time_value_t start_clock, time_value_t end_clock) {
     return duration_clock;
 }
 
+static double wall_interval_in_ms(uint64_t elapsed) {
+    mach_timebase_info_data_t sTimebaseInfo;
+    if (KERN_SUCCESS != mach_timebase_info(&sTimebaseInfo)) {
+        return 0;
+    } else {
+        uint64_t elapsedNano = elapsed * sTimebaseInfo.numer / sTimebaseInfo.denom;
+        return elapsedNano / 1000000.0;
+    }
+}
+
 void SysTimer::startWall() {
     fStartWall = mach_absolute_time();
 }
@@ -54,13 +64,10 @@ double SysTimer::endCpu() {
 
 double SysTimer::endWall() {
     uint64_t end_wall = mach_absolute_time();
+    return wall_interval_in_ms(end_wall - fStartWall);
+}
 
-    uint64_t elapsed = end_wall - fStartWall;
-    mach_timebase_info_data_t sTimebaseInfo;
-    if (KERN_SUCCESS != mach_timebase_info(&sTimebaseInfo)) {
-        return 0;
-    } else {
-        uint64_t elapsedNano = elapsed * sTimebaseInfo.numer / sTimebaseInfo.denom;
-        return elapsedNano / 1000000.0;
-    }
+double GetTimeMs() {
+    static const uint64_t launchTime = mach_absolute_time();
+    return wall_interval_in_ms(mach_absolute_time() - launchTime);
 }