win: Fix ClockMonotonicNanoseconds()

util/misc/clock_win.cc

 // Copyright 2014 The Crashpad Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 21 matching lines @@
 
 }  // namespace
 
 namespace crashpad {
 
 uint64_t ClockMonotonicNanoseconds() {
   LARGE_INTEGER time;
   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);
 }
 
 }  // namespace crashpad