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authorGravatar Abseil Team <absl-team@google.com>2017-10-10 17:07:46 -0700
committerGravatar Gennadiy Rozental <rogeeff@gmail.com>2017-10-11 11:01:17 -0400
commit029795a9b5281379f892fbbe3f9a400d5a33f5cc (patch)
treeb461dbd4c1e212917a0f849e1e0dfc4c036f7ee7 /absl/time/time.h
parent962e9931d546cd6f062894e15283cea02c7d3220 (diff)
Changes imported from Abseil "staging" branch:
- 3e05f2c346a9faf07088c49d590d49a9199e7edd Simplify Duration's operator-() by Jorg Brown <jorg@google.com> - 3c4942375a6d17e887bb6ab7cf2d0e763d58a511 Rewrite `noexcept(noexcept(allocator_type()))` to instead... by Matt Calabrese <calabrese@google.com> - 02f35a684201a6aa9f70e8b0a041993676f2d230 Fix comment on remove_prefix since the function is not re... by Abseil Team <absl-team@google.com> - ceb40aba8031e0ccec9cd49da844882df100c56f Fix mutex_test under TSAN. by Derek Mauro <dmauro@google.com> - 7bd12e7ddc5d074e1b9c9f037879211fa1d81f8c Slight wording tweaks for "adopting" wrappers by Abseil Team <absl-team@google.com> - c3580afe092e0357d40b1769314f36da1b887c65 Internal cleanup. by Greg Miller <jgm@google.com> GitOrigin-RevId: 3e05f2c346a9faf07088c49d590d49a9199e7edd Change-Id: If3df72fba3803398cfcbb323fb4cb84ec55511aa
Diffstat (limited to 'absl/time/time.h')
-rw-r--r--absl/time/time.h37
1 files changed, 17 insertions, 20 deletions
diff --git a/absl/time/time.h b/absl/time/time.h
index 093f168d..c01977b0 100644
--- a/absl/time/time.h
+++ b/absl/time/time.h
@@ -1126,8 +1126,10 @@ constexpr Duration OppositeInfinity(Duration d) {
: MakeDuration(std::numeric_limits<int64_t>::min(), ~0U);
}
-// Returns (-n)-1 (equivalently -(n+1)) without overflowing on any input value.
+// Returns (-n)-1 (equivalently -(n+1)) without avoidable overflow.
constexpr int64_t NegateAndSubtractOne(int64_t n) {
+ // Note: Good compilers will optimize this expression to ~n when using
+ // a two's-complement representation (which is required for int64_t).
return (n < 0) ? -(n + 1) : (-n) - 1;
}
@@ -1232,31 +1234,26 @@ constexpr bool operator==(Duration lhs, Duration rhs) {
constexpr Duration operator-(Duration d) {
// This is a little interesting because of the special cases.
//
- // Infinities stay infinite, and just change direction.
+ // If rep_lo_ is zero, we have it easy; it's safe to negate rep_hi_, we're
+ // dealing with an integral number of seconds, and the only special case is
+ // the maximum negative finite duration, which can't be negated.
//
- // The maximum negative finite duration can't be negated (at least, not
- // on a two's complement machine), so we return infinity for that case.
- // Next we dispatch the case where rep_lo_ is zero, observing that it's
- // safe to negate rep_hi_ in this case because it's not int64_t-min (or
- // else we'd have handled it above, returning InfiniteDuration()).
+ // Infinities stay infinite, and just change direction.
//
// Finally we're in the case where rep_lo_ is non-zero, and we can borrow
// a second's worth of ticks and avoid overflow (as negating int64_t-min + 1
// is safe).
- return time_internal::IsInfiniteDuration(d)
- ? time_internal::OppositeInfinity(d)
- : (time_internal::GetRepHi(d) ==
- std::numeric_limits<int64_t>::min() &&
- time_internal::GetRepLo(d) == 0)
+ return time_internal::GetRepLo(d) == 0
+ ? time_internal::GetRepHi(d) == std::numeric_limits<int64_t>::min()
? InfiniteDuration()
- : (time_internal::GetRepLo(d) == 0)
- ? time_internal::MakeDuration(
- -time_internal::GetRepHi(d))
- : time_internal::MakeDuration(
- time_internal::NegateAndSubtractOne(
- time_internal::GetRepHi(d)),
- time_internal::kTicksPerSecond -
- time_internal::GetRepLo(d));
+ : time_internal::MakeDuration(-time_internal::GetRepHi(d))
+ : time_internal::IsInfiniteDuration(d)
+ ? time_internal::OppositeInfinity(d)
+ : time_internal::MakeDuration(
+ time_internal::NegateAndSubtractOne(
+ time_internal::GetRepHi(d)),
+ time_internal::kTicksPerSecond -
+ time_internal::GetRepLo(d));
}
constexpr Duration Nanoseconds(int64_t n) {