diff options
Diffstat (limited to 'absl/time/time.h')
| -rw-r--r-- | absl/time/time.h | 37 |
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) { |