BenchSysTimer_mach drops all sub-ms precision. Fix that!

bench/BenchSysTimer_mach.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 "BenchSysTimer_mach.h"
 
 //Time
@@ skipping 53 matching lines @@
 double BenchSysTimer::endWall() {
     uint64_t end_wall = mach_absolute_time();
 
     uint64_t elapsed = end_wall - this->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;
+        return elapsedNano / 1000000.0;
     }
 }