util/win/time.cc: Add and use FiletimeToMicroseconds()

util/win/time.cc

Index: util/win/time.cc
diff --git a/util/win/time.cc b/util/win/time.cc
index 8e4760bb13cd92ad700a357fb4f83fea0120fe11..1665b9c6efbb9b25746576694d84c52374c31744 100644
--- a/util/win/time.cc
+++ b/util/win/time.cc
@@ -24,34 +24,36 @@ namespace {
 
 const uint64_t kMicrosecondsPerSecond = static_cast<uint64_t>(1E6);
 
-timeval MicrosecondsToTimeval(uint64_t t) {
+uint64_t FiletimeToMicroseconds(const FILETIME& filetime) {
+  uint64_t t = (static_cast<uint64_t>(filetime.dwHighDateTime) << 32) |
+               filetime.dwLowDateTime;
+  return t / 10;  // 100 nanosecond intervals to microseconds.
+}
+
+timeval MicrosecondsToTimeval(uint64_t microseconds) {
   timeval tv;
-  tv.tv_sec = static_cast<long>(t / kMicrosecondsPerSecond);
-  tv.tv_usec = static_cast<long>(t % kMicrosecondsPerSecond);
+  tv.tv_sec = static_cast<long>(microseconds / kMicrosecondsPerSecond);
+  tv.tv_usec = static_cast<long>(microseconds % kMicrosecondsPerSecond);
   return tv;
 }
 
 }  // namespace
 
 timeval FiletimeToTimevalEpoch(const FILETIME& filetime) {
-  uint64_t t = (static_cast<uint64_t>(filetime.dwHighDateTime) << 32) |
-               filetime.dwLowDateTime;
-  t /= 10;  // 100 nanosecond intervals to microseconds.
+  uint64_t microseconds = FiletimeToMicroseconds(filetime);
+
   // Windows epoch is 1601-01-01, and FILETIME ticks are 100 nanoseconds.
   // 1601 to 1970 is 369 years + 89 leap days = 134774 days * 86400 seconds per
   // day. It's not entirely clear, but it appears that these are solar seconds,
   // not SI seconds, so there are no leap seconds to be considered.
   const uint64_t kNumSecondsFrom1601To1970 = (369 * 365 + 89) * 86400ULL;
-  DCHECK_GE(t, kNumSecondsFrom1601To1970 * kMicrosecondsPerSecond);
-  t -= kNumSecondsFrom1601To1970 * kMicrosecondsPerSecond;
-  return MicrosecondsToTimeval(t);
+  DCHECK_GE(microseconds, kNumSecondsFrom1601To1970 * kMicrosecondsPerSecond);
+  microseconds -= kNumSecondsFrom1601To1970 * kMicrosecondsPerSecond;
+  return MicrosecondsToTimeval(microseconds);
 }
 
 timeval FiletimeToTimevalInterval(const FILETIME& filetime) {
-  uint64_t t = (static_cast<uint64_t>(filetime.dwHighDateTime) << 32) |
-               filetime.dwLowDateTime;
-  t /= 10;  // 100 nanosecond intervals to microseconds.
-  return MicrosecondsToTimeval(t);
+  return MicrosecondsToTimeval(FiletimeToMicroseconds(filetime));
 }
 
 void GetTimeOfDay(timeval* tv) {