win: Fix ClockMonotonicNanoseconds()

util/misc/clock_win.cc

Index: util/misc/clock_win.cc
diff --git a/util/misc/clock_win.cc b/util/misc/clock_win.cc
index 731e98d4ee29da76306d598f4ee02ec64cffa99d..7231205decef22842a4a65745dcfe268ed40e0c6 100644
--- a/util/misc/clock_win.cc
+++ b/util/misc/clock_win.cc
@@ -39,7 +39,7 @@ uint64_t ClockMonotonicNanoseconds() {
   QueryPerformanceCounter(&time);
   int64_t frequency = QpcFrequency();
   int64_t whole_seconds = time.QuadPart / frequency;
-  int64_t leftover_ticks = time.QuadPart / (whole_seconds * frequency);
+  int64_t leftover_ticks = time.QuadPart % frequency;

[scottmg, 2015/11/05 18:49:58]

frequency = 10, time.QuadPart = 98

whole_seconds = 98 / 10 = 9
leftover_ticks_old = 98 / 90 = 0
leftover_ticks_new = 98 % 10 = 8

result_nano = 9 * to_nano + 8 * to_nano / freq

Yup, no idea what I was doing. :/

[Mark Mentovai, 2015/11/05 18:58:10]

scottmg wrote:
I think you meant - instead of / on this line, but the % is just as good if not
better.

   const int64_t kNanosecondsPerSecond = static_cast<const int64_t>(1E9);
   return (whole_seconds * kNanosecondsPerSecond) +
          ((leftover_ticks * kNanosecondsPerSecond) / frequency);