Get rid of tail padding within `absl::Duration`. This reduces memory usage needs when storing duration in containers (e.g. `vector<absl::Duration>` uses 25% less memory), and allows classes with `absl::Duration` fields to fit other stuff in memory previously used by tail padding (e.g. `std::optional<absl::Duration>` is now 16 bytes instead of 24).
PiperOrigin-RevId: 506568782
Change-Id: Ic9e077f02a80da013fb2d312aff77761b970c07a
diff --git a/absl/time/duration.cc b/absl/time/duration.cc
index b915d74..911e80f 100644
--- a/absl/time/duration.cc
+++ b/absl/time/duration.cc
@@ -407,18 +407,16 @@
Duration& Duration::operator+=(Duration rhs) {
if (time_internal::IsInfiniteDuration(*this)) return *this;
if (time_internal::IsInfiniteDuration(rhs)) return *this = rhs;
- const int64_t orig_rep_hi = rep_hi_.Get();
- rep_hi_ = DecodeTwosComp(EncodeTwosComp(rep_hi_.Get()) +
- EncodeTwosComp(rhs.rep_hi_.Get()));
+ const int64_t orig_rep_hi = rep_hi_;
+ rep_hi_ =
+ DecodeTwosComp(EncodeTwosComp(rep_hi_) + EncodeTwosComp(rhs.rep_hi_));
if (rep_lo_ >= kTicksPerSecond - rhs.rep_lo_) {
- rep_hi_ = DecodeTwosComp(EncodeTwosComp(rep_hi_.Get()) + 1);
+ rep_hi_ = DecodeTwosComp(EncodeTwosComp(rep_hi_) + 1);
rep_lo_ -= kTicksPerSecond;
}
rep_lo_ += rhs.rep_lo_;
- if (rhs.rep_hi_.Get() < 0 ? rep_hi_.Get() > orig_rep_hi
- : rep_hi_.Get() < orig_rep_hi) {
- return *this =
- rhs.rep_hi_.Get() < 0 ? -InfiniteDuration() : InfiniteDuration();
+ if (rhs.rep_hi_ < 0 ? rep_hi_ > orig_rep_hi : rep_hi_ < orig_rep_hi) {
+ return *this = rhs.rep_hi_ < 0 ? -InfiniteDuration() : InfiniteDuration();
}
return *this;
}
@@ -426,21 +424,18 @@
Duration& Duration::operator-=(Duration rhs) {
if (time_internal::IsInfiniteDuration(*this)) return *this;
if (time_internal::IsInfiniteDuration(rhs)) {
- return *this = rhs.rep_hi_.Get() >= 0 ? -InfiniteDuration()
- : InfiniteDuration();
+ return *this = rhs.rep_hi_ >= 0 ? -InfiniteDuration() : InfiniteDuration();
}
- const int64_t orig_rep_hi = rep_hi_.Get();
- rep_hi_ = DecodeTwosComp(EncodeTwosComp(rep_hi_.Get()) -
- EncodeTwosComp(rhs.rep_hi_.Get()));
+ const int64_t orig_rep_hi = rep_hi_;
+ rep_hi_ =
+ DecodeTwosComp(EncodeTwosComp(rep_hi_) - EncodeTwosComp(rhs.rep_hi_));
if (rep_lo_ < rhs.rep_lo_) {
- rep_hi_ = DecodeTwosComp(EncodeTwosComp(rep_hi_.Get()) - 1);
+ rep_hi_ = DecodeTwosComp(EncodeTwosComp(rep_hi_) - 1);
rep_lo_ += kTicksPerSecond;
}
rep_lo_ -= rhs.rep_lo_;
- if (rhs.rep_hi_.Get() < 0 ? rep_hi_.Get() < orig_rep_hi
- : rep_hi_.Get() > orig_rep_hi) {
- return *this = rhs.rep_hi_.Get() >= 0 ? -InfiniteDuration()
- : InfiniteDuration();
+ if (rhs.rep_hi_ < 0 ? rep_hi_ < orig_rep_hi : rep_hi_ > orig_rep_hi) {
+ return *this = rhs.rep_hi_ >= 0 ? -InfiniteDuration() : InfiniteDuration();
}
return *this;
}
@@ -451,7 +446,7 @@
Duration& Duration::operator*=(int64_t r) {
if (time_internal::IsInfiniteDuration(*this)) {
- const bool is_neg = (r < 0) != (rep_hi_.Get() < 0);
+ const bool is_neg = (r < 0) != (rep_hi_ < 0);
return *this = is_neg ? -InfiniteDuration() : InfiniteDuration();
}
return *this = ScaleFixed<SafeMultiply>(*this, r);
@@ -459,7 +454,7 @@
Duration& Duration::operator*=(double r) {
if (time_internal::IsInfiniteDuration(*this) || !IsFinite(r)) {
- const bool is_neg = std::signbit(r) != (rep_hi_.Get() < 0);
+ const bool is_neg = (std::signbit(r) != 0) != (rep_hi_ < 0);
return *this = is_neg ? -InfiniteDuration() : InfiniteDuration();
}
return *this = ScaleDouble<std::multiplies>(*this, r);
@@ -467,7 +462,7 @@
Duration& Duration::operator/=(int64_t r) {
if (time_internal::IsInfiniteDuration(*this) || r == 0) {
- const bool is_neg = (r < 0) != (rep_hi_.Get() < 0);
+ const bool is_neg = (r < 0) != (rep_hi_ < 0);
return *this = is_neg ? -InfiniteDuration() : InfiniteDuration();
}
return *this = ScaleFixed<std::divides>(*this, r);
@@ -475,7 +470,7 @@
Duration& Duration::operator/=(double r) {
if (time_internal::IsInfiniteDuration(*this) || !IsValidDivisor(r)) {
- const bool is_neg = std::signbit(r) != (rep_hi_.Get() < 0);
+ const bool is_neg = (std::signbit(r) != 0) != (rep_hi_ < 0);
return *this = is_neg ? -InfiniteDuration() : InfiniteDuration();
}
return *this = ScaleDouble<std::divides>(*this, r);
diff --git a/absl/time/duration_test.cc b/absl/time/duration_test.cc
index 84224f4..b7abf4b 100644
--- a/absl/time/duration_test.cc
+++ b/absl/time/duration_test.cc
@@ -16,9 +16,8 @@
#include <winsock2.h> // for timeval
#endif
-#include <array>
-#include <cfloat>
#include <chrono> // NOLINT(build/c++11)
+#include <cfloat>
#include <cmath>
#include <cstdint>
#include <ctime>
@@ -1854,11 +1853,4 @@
#undef TEST_PARSE_ROUNDTRIP
}
-TEST(Duration, NoPadding) {
- // Should match the size of a struct with uint32_t alignment and no padding.
- using NoPadding = std::array<uint32_t, 3>;
- EXPECT_EQ(sizeof(NoPadding), sizeof(absl::Duration));
- EXPECT_EQ(alignof(NoPadding), alignof(absl::Duration));
-}
-
} // namespace
diff --git a/absl/time/time.h b/absl/time/time.h
index bf1007c..cc39008 100644
--- a/absl/time/time.h
+++ b/absl/time/time.h
@@ -84,7 +84,6 @@
#include <type_traits>
#include <utility>
-#include "absl/base/config.h"
#include "absl/base/macros.h"
#include "absl/strings/string_view.h"
#include "absl/time/civil_time.h"
@@ -215,7 +214,7 @@
template <typename H>
friend H AbslHashValue(H h, Duration d) {
- return H::combine(std::move(h), d.rep_hi_.Get(), d.rep_lo_);
+ return H::combine(std::move(h), d.rep_hi_, d.rep_lo_);
}
private:
@@ -224,73 +223,7 @@
friend constexpr Duration time_internal::MakeDuration(int64_t hi,
uint32_t lo);
constexpr Duration(int64_t hi, uint32_t lo) : rep_hi_(hi), rep_lo_(lo) {}
-
- // We store `hi_rep_` 4-byte rather than 8-byte aligned to avoid 4 bytes of
- // tail padding.
- class HiRep {
- public:
- // Default constructor default-initializes `hi_`, which has the same
- // semantics as default-initializing an `int64_t` (undetermined value).
- HiRep() = default;
-
- HiRep(const HiRep&) = default;
- HiRep& operator=(const HiRep&) = default;
-
- explicit constexpr HiRep(const int64_t value)
- : // C++17 forbids default-initialization in constexpr contexts. We can
- // remove this in C++20.
- lo_(0),
- hi_(0) {
- *this = value;
- }
-
- constexpr int64_t Get() const {
- const uint64_t unsigned_value =
- (static_cast<uint64_t>(hi_) << 32) | static_cast<uint64_t>(lo_);
- // `static_cast<int64_t>(unsigned_value)` is implementation-defined
- // before c++20. On all supported platforms the behaviour is that mandated
- // by c++20, i.e. "If the destination type is signed, [...] the result is
- // the unique value of the destination type equal to the source value
- // modulo 2^n, where n is the number of bits used to represent the
- // destination type."
- static_assert(
- (static_cast<int64_t>((std::numeric_limits<uint64_t>::max)()) ==
- int64_t{-1}) &&
- (static_cast<int64_t>(static_cast<uint64_t>(
- (std::numeric_limits<int64_t>::max)()) +
- 1) ==
- (std::numeric_limits<int64_t>::min)()),
- "static_cast<int64_t>(uint64_t) does not have c++20 semantics");
- return static_cast<int64_t>(unsigned_value);
- }
-
- constexpr HiRep& operator=(const int64_t value) {
- // "If the destination type is unsigned, the resulting value is the
- // smallest unsigned value equal to the source value modulo 2^n
- // where `n` is the number of bits used to represent the destination
- // type".
- const auto unsigned_value = static_cast<uint64_t>(value);
- hi_ = static_cast<uint32_t>(unsigned_value >> 32);
- lo_ = static_cast<uint32_t>(unsigned_value);
- return *this;
- }
-
- private:
- // Notes:
- // - Ideally we would use a `char[]` and `std::bitcast`, but the latter
- // does not exist (and is not constexpr in `absl`) before c++20.
- // - Order is optimized depending on endianness so that the compiler can
- // turn `Get()` (resp. `operator=()`) into a single 8-byte load (resp.
- // store).
-#if defined(ABSL_IS_BIG_ENDIAN) && ABSL_IS_BIG_ENDIAN
- uint32_t hi_;
- uint32_t lo_;
-#else
- uint32_t lo_;
- uint32_t hi_;
-#endif
- };
- HiRep rep_hi_;
+ int64_t rep_hi_;
uint32_t rep_lo_;
};
@@ -1558,7 +1491,7 @@
// Provide access to the Duration representation.
ABSL_ATTRIBUTE_CONST_FUNCTION constexpr int64_t GetRepHi(Duration d) {
- return d.rep_hi_.Get();
+ return d.rep_hi_;
}
ABSL_ATTRIBUTE_CONST_FUNCTION constexpr uint32_t GetRepLo(Duration d) {
return d.rep_lo_;
