win: add equivalent of gettimeofday

util/win/time.cc

+// Copyright 2015 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,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "util/win/time.h"
+
+#include <inttypes.h>
+#include <windows.h>
+
+namespace crashpad {
+
+void GetTimeOfDay(timeval* tv) {

[Mark Mentovai, 2015/02/20 18:15:33]

Maybe we want to do this in compat as gettimeofday() instead of here. That would
make more sense if there were cross-platform callers. If there aren’t, this is
fine.

[scottmg, 2015/02/20 19:27:56]

There isn't at the moment, so I'll leave it here. We can always move it later.

+  FILETIME filetime;
+  GetSystemTimeAsFileTime(&filetime);
+  uint64_t t = (static_cast<uint64_t>(filetime.dwHighDateTime) << 32) |
+               filetime.dwLowDateTime;
+  t /= 10;  // 100 nanosecond intervals to microseconds.
+  // 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 = 11644473600;

[Mark Mentovai, 2015/02/20 18:15:33]

This would be more convincing if it did the math in-line: (369 * 365 + 89) * (24
* 60 * 60).

(You could use 86400 for the last term, I recognize it and you did mention it in
the comment.)

[scottmg, 2015/02/20 19:27:56]

Done.

+  const uint64_t kMicrosecondsPerSecond = 1000000;

[Mark Mentovai, 2015/02/20 18:15:33]

Counting zeroes is hard, use 1E6.

[scottmg, 2015/02/20 19:27:56]

Done.

+  t -= kNumSecondsFrom1601To1970 * kMicrosecondsPerSecond;

[Mark Mentovai, 2015/02/20 18:15:33]

DCHECK_GE(t, kNumSecondsFrom1601To1970) before subtracting.

[scottmg, 2015/02/20 19:27:56]

Done.

+  tv->tv_sec = static_cast<long>(t / kMicrosecondsPerSecond);
+  tv->tv_usec = static_cast<long>(t % kMicrosecondsPerSecond);
+}
+
+}  // namespace crashpad