Add 'third_party/abseil_cpp/' from commit '768eb2ca2857342673fcd462792ce04b8bac3fa3' r/781

git-subtree-dir: third_party/abseil_cpp
git-subtree-mainline: ffb2ae54beb5796cd408fbe15d2d2da09ff37adf
git-subtree-split: 768eb2ca2857342673fcd462792ce04b8bac3fa3

1 files changed, 951 insertions, 0 deletions

diff --git a/third_party/abseil_cpp/absl/time/duration.cc b/third_party/abseil_cpp/absl/time/duration.cc
new file mode 100644
index 0000000000..d0f1aadbf2
--- /dev/null
+++ b/third_party/abseil_cpp/absl/time/duration.cc
@@ -0,0 +1,951 @@
+// Copyright 2017 The Abseil Authors.
+//
+// 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
+//
+//      https://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.
+
+// The implementation of the absl::Duration class, which is declared in
+// //absl/time.h.  This class behaves like a numeric type; it has no public
+// methods and is used only through the operators defined here.
+//
+// Implementation notes:
+//
+// An absl::Duration is represented as
+//
+//   rep_hi_ : (int64_t)  Whole seconds
+//   rep_lo_ : (uint32_t) Fractions of a second
+//
+// The seconds value (rep_hi_) may be positive or negative as appropriate.
+// The fractional seconds (rep_lo_) is always a positive offset from rep_hi_.
+// The API for Duration guarantees at least nanosecond resolution, which
+// means rep_lo_ could have a max value of 1B - 1 if it stored nanoseconds.
+// However, to utilize more of the available 32 bits of space in rep_lo_,
+// we instead store quarters of a nanosecond in rep_lo_ resulting in a max
+// value of 4B - 1.  This allows us to correctly handle calculations like
+// 0.5 nanos + 0.5 nanos = 1 nano.  The following example shows the actual
+// Duration rep using quarters of a nanosecond.
+//
+//    2.5 sec = {rep_hi_=2,  rep_lo_=2000000000}  // lo = 4 * 500000000
+//   -2.5 sec = {rep_hi_=-3, rep_lo_=2000000000}
+//
+// Infinite durations are represented as Durations with the rep_lo_ field set
+// to all 1s.
+//
+//   +InfiniteDuration:
+//     rep_hi_ : kint64max
+//     rep_lo_ : ~0U
+//
+//   -InfiniteDuration:
+//     rep_hi_ : kint64min
+//     rep_lo_ : ~0U
+//
+// Arithmetic overflows/underflows to +/- infinity and saturates.
+
+#if defined(_MSC_VER)
+#include <winsock2.h>  // for timeval
+#endif
+
+#include <algorithm>
+#include <cassert>
+#include <cctype>
+#include <cerrno>
+#include <cmath>
+#include <cstdint>
+#include <cstdlib>
+#include <cstring>
+#include <ctime>
+#include <functional>
+#include <limits>
+#include <string>
+
+#include "absl/base/casts.h"
+#include "absl/base/macros.h"
+#include "absl/numeric/int128.h"
+#include "absl/strings/strip.h"
+#include "absl/time/time.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+namespace {
+
+using time_internal::kTicksPerNanosecond;
+using time_internal::kTicksPerSecond;
+
+constexpr int64_t kint64max = std::numeric_limits<int64_t>::max();
+constexpr int64_t kint64min = std::numeric_limits<int64_t>::min();
+
+// Can't use std::isinfinite() because it doesn't exist on windows.
+inline bool IsFinite(double d) {
+  if (std::isnan(d)) return false;
+  return d != std::numeric_limits<double>::infinity() &&
+         d != -std::numeric_limits<double>::infinity();
+}
+
+inline bool IsValidDivisor(double d) {
+  if (std::isnan(d)) return false;
+  return d != 0.0;
+}
+
+// Can't use std::round() because it is only available in C++11.
+// Note that we ignore the possibility of floating-point over/underflow.
+template <typename Double>
+inline double Round(Double d) {
+  return d < 0 ? std::ceil(d - 0.5) : std::floor(d + 0.5);
+}
+
+// *sec may be positive or negative.  *ticks must be in the range
+// -kTicksPerSecond < *ticks < kTicksPerSecond.  If *ticks is negative it
+// will be normalized to a positive value by adjusting *sec accordingly.
+inline void NormalizeTicks(int64_t* sec, int64_t* ticks) {
+  if (*ticks < 0) {
+    --*sec;
+    *ticks += kTicksPerSecond;
+  }
+}
+
+// Makes a uint128 from the absolute value of the given scalar.
+inline uint128 MakeU128(int64_t a) {
+  uint128 u128 = 0;
+  if (a < 0) {
+    ++u128;
+    ++a;  // Makes it safe to negate 'a'
+    a = -a;
+  }
+  u128 += static_cast<uint64_t>(a);
+  return u128;
+}
+
+// Makes a uint128 count of ticks out of the absolute value of the Duration.
+inline uint128 MakeU128Ticks(Duration d) {
+  int64_t rep_hi = time_internal::GetRepHi(d);
+  uint32_t rep_lo = time_internal::GetRepLo(d);
+  if (rep_hi < 0) {
+    ++rep_hi;
+    rep_hi = -rep_hi;
+    rep_lo = kTicksPerSecond - rep_lo;
+  }
+  uint128 u128 = static_cast<uint64_t>(rep_hi);
+  u128 *= static_cast<uint64_t>(kTicksPerSecond);
+  u128 += rep_lo;
+  return u128;
+}
+
+// Breaks a uint128 of ticks into a Duration.
+inline Duration MakeDurationFromU128(uint128 u128, bool is_neg) {
+  int64_t rep_hi;
+  uint32_t rep_lo;
+  const uint64_t h64 = Uint128High64(u128);
+  const uint64_t l64 = Uint128Low64(u128);
+  if (h64 == 0) {  // fastpath
+    const uint64_t hi = l64 / kTicksPerSecond;
+    rep_hi = static_cast<int64_t>(hi);
+    rep_lo = static_cast<uint32_t>(l64 - hi * kTicksPerSecond);
+  } else {
+    // kMaxRepHi64 is the high 64 bits of (2^63 * kTicksPerSecond).
+    // Any positive tick count whose high 64 bits are >= kMaxRepHi64
+    // is not representable as a Duration.  A negative tick count can
+    // have its high 64 bits == kMaxRepHi64 but only when the low 64
+    // bits are all zero, otherwise it is not representable either.
+    const uint64_t kMaxRepHi64 = 0x77359400UL;
+    if (h64 >= kMaxRepHi64) {
+      if (is_neg && h64 == kMaxRepHi64 && l64 == 0) {
+        // Avoid trying to represent -kint64min below.
+        return time_internal::MakeDuration(kint64min);
+      }
+      return is_neg ? -InfiniteDuration() : InfiniteDuration();
+    }
+    const uint128 kTicksPerSecond128 = static_cast<uint64_t>(kTicksPerSecond);
+    const uint128 hi = u128 / kTicksPerSecond128;
+    rep_hi = static_cast<int64_t>(Uint128Low64(hi));
+    rep_lo =
+        static_cast<uint32_t>(Uint128Low64(u128 - hi * kTicksPerSecond128));
+  }
+  if (is_neg) {
+    rep_hi = -rep_hi;
+    if (rep_lo != 0) {
+      --rep_hi;
+      rep_lo = kTicksPerSecond - rep_lo;
+    }
+  }
+  return time_internal::MakeDuration(rep_hi, rep_lo);
+}
+
+// Convert between int64_t and uint64_t, preserving representation. This
+// allows us to do arithmetic in the unsigned domain, where overflow has
+// well-defined behavior. See operator+=() and operator-=().
+//
+// C99 7.20.1.1.1, as referenced by C++11 18.4.1.2, says, "The typedef
+// name intN_t designates a signed integer type with width N, no padding
+// bits, and a two's complement representation." So, we can convert to
+// and from the corresponding uint64_t value using a bit cast.
+inline uint64_t EncodeTwosComp(int64_t v) {
+  return absl::bit_cast<uint64_t>(v);
+}
+inline int64_t DecodeTwosComp(uint64_t v) { return absl::bit_cast<int64_t>(v); }
+
+// Note: The overflow detection in this function is done using greater/less *or
+// equal* because kint64max/min is too large to be represented exactly in a
+// double (which only has 53 bits of precision). In order to avoid assigning to
+// rep->hi a double value that is too large for an int64_t (and therefore is
+// undefined), we must consider computations that equal kint64max/min as a
+// double as overflow cases.
+inline bool SafeAddRepHi(double a_hi, double b_hi, Duration* d) {
+  double c = a_hi + b_hi;
+  if (c >= static_cast<double>(kint64max)) {
+    *d = InfiniteDuration();
+    return false;
+  }
+  if (c <= static_cast<double>(kint64min)) {
+    *d = -InfiniteDuration();
+    return false;
+  }
+  *d = time_internal::MakeDuration(c, time_internal::GetRepLo(*d));
+  return true;
+}
+
+// A functor that's similar to std::multiplies<T>, except this returns the max
+// T value instead of overflowing. This is only defined for uint128.
+template <typename Ignored>
+struct SafeMultiply {
+  uint128 operator()(uint128 a, uint128 b) const {
+    // b hi is always zero because it originated as an int64_t.
+    assert(Uint128High64(b) == 0);
+    // Fastpath to avoid the expensive overflow check with division.
+    if (Uint128High64(a) == 0) {
+      return (((Uint128Low64(a) | Uint128Low64(b)) >> 32) == 0)
+                 ? static_cast<uint128>(Uint128Low64(a) * Uint128Low64(b))
+                 : a * b;
+    }
+    return b == 0 ? b : (a > kuint128max / b) ? kuint128max : a * b;
+  }
+};
+
+// Scales (i.e., multiplies or divides, depending on the Operation template)
+// the Duration d by the int64_t r.
+template <template <typename> class Operation>
+inline Duration ScaleFixed(Duration d, int64_t r) {
+  const uint128 a = MakeU128Ticks(d);
+  const uint128 b = MakeU128(r);
+  const uint128 q = Operation<uint128>()(a, b);
+  const bool is_neg = (time_internal::GetRepHi(d) < 0) != (r < 0);
+  return MakeDurationFromU128(q, is_neg);
+}
+
+// Scales (i.e., multiplies or divides, depending on the Operation template)
+// the Duration d by the double r.
+template <template <typename> class Operation>
+inline Duration ScaleDouble(Duration d, double r) {
+  Operation<double> op;
+  double hi_doub = op(time_internal::GetRepHi(d), r);
+  double lo_doub = op(time_internal::GetRepLo(d), r);
+
+  double hi_int = 0;
+  double hi_frac = std::modf(hi_doub, &hi_int);
+
+  // Moves hi's fractional bits to lo.
+  lo_doub /= kTicksPerSecond;
+  lo_doub += hi_frac;
+
+  double lo_int = 0;
+  double lo_frac = std::modf(lo_doub, &lo_int);
+
+  // Rolls lo into hi if necessary.
+  int64_t lo64 = Round(lo_frac * kTicksPerSecond);
+
+  Duration ans;
+  if (!SafeAddRepHi(hi_int, lo_int, &ans)) return ans;
+  int64_t hi64 = time_internal::GetRepHi(ans);
+  if (!SafeAddRepHi(hi64, lo64 / kTicksPerSecond, &ans)) return ans;
+  hi64 = time_internal::GetRepHi(ans);
+  lo64 %= kTicksPerSecond;
+  NormalizeTicks(&hi64, &lo64);
+  return time_internal::MakeDuration(hi64, lo64);
+}
+
+// Tries to divide num by den as fast as possible by looking for common, easy
+// cases. If the division was done, the quotient is in *q and the remainder is
+// in *rem and true will be returned.
+inline bool IDivFastPath(const Duration num, const Duration den, int64_t* q,
+                         Duration* rem) {
+  // Bail if num or den is an infinity.
+  if (time_internal::IsInfiniteDuration(num) ||
+      time_internal::IsInfiniteDuration(den))
+    return false;
+
+  int64_t num_hi = time_internal::GetRepHi(num);
+  uint32_t num_lo = time_internal::GetRepLo(num);
+  int64_t den_hi = time_internal::GetRepHi(den);
+  uint32_t den_lo = time_internal::GetRepLo(den);
+
+  if (den_hi == 0 && den_lo == kTicksPerNanosecond) {
+    // Dividing by 1ns
+    if (num_hi >= 0 && num_hi < (kint64max - kTicksPerSecond) / 1000000000) {
+      *q = num_hi * 1000000000 + num_lo / kTicksPerNanosecond;
+      *rem = time_internal::MakeDuration(0, num_lo % den_lo);
+      return true;
+    }
+  } else if (den_hi == 0 && den_lo == 100 * kTicksPerNanosecond) {
+    // Dividing by 100ns (common when converting to Universal time)
+    if (num_hi >= 0 && num_hi < (kint64max - kTicksPerSecond) / 10000000) {
+      *q = num_hi * 10000000 + num_lo / (100 * kTicksPerNanosecond);
+      *rem = time_internal::MakeDuration(0, num_lo % den_lo);
+      return true;
+    }
+  } else if (den_hi == 0 && den_lo == 1000 * kTicksPerNanosecond) {
+    // Dividing by 1us
+    if (num_hi >= 0 && num_hi < (kint64max - kTicksPerSecond) / 1000000) {
+      *q = num_hi * 1000000 + num_lo / (1000 * kTicksPerNanosecond);
+      *rem = time_internal::MakeDuration(0, num_lo % den_lo);
+      return true;
+    }
+  } else if (den_hi == 0 && den_lo == 1000000 * kTicksPerNanosecond) {
+    // Dividing by 1ms
+    if (num_hi >= 0 && num_hi < (kint64max - kTicksPerSecond) / 1000) {
+      *q = num_hi * 1000 + num_lo / (1000000 * kTicksPerNanosecond);
+      *rem = time_internal::MakeDuration(0, num_lo % den_lo);
+      return true;
+    }
+  } else if (den_hi > 0 && den_lo == 0) {
+    // Dividing by positive multiple of 1s
+    if (num_hi >= 0) {
+      if (den_hi == 1) {
+        *q = num_hi;
+        *rem = time_internal::MakeDuration(0, num_lo);
+        return true;
+      }
+      *q = num_hi / den_hi;
+      *rem = time_internal::MakeDuration(num_hi % den_hi, num_lo);
+      return true;
+    }
+    if (num_lo != 0) {
+      num_hi += 1;
+    }
+    int64_t quotient = num_hi / den_hi;
+    int64_t rem_sec = num_hi % den_hi;
+    if (rem_sec > 0) {
+      rem_sec -= den_hi;
+      quotient += 1;
+    }
+    if (num_lo != 0) {
+      rem_sec -= 1;
+    }
+    *q = quotient;
+    *rem = time_internal::MakeDuration(rem_sec, num_lo);
+    return true;
+  }
+
+  return false;
+}
+
+}  // namespace
+
+namespace time_internal {
+
+// The 'satq' argument indicates whether the quotient should saturate at the
+// bounds of int64_t.  If it does saturate, the difference will spill over to
+// the remainder.  If it does not saturate, the remainder remain accurate,
+// but the returned quotient will over/underflow int64_t and should not be used.
+int64_t IDivDuration(bool satq, const Duration num, const Duration den,
+                   Duration* rem) {
+  int64_t q = 0;
+  if (IDivFastPath(num, den, &q, rem)) {
+    return q;
+  }
+
+  const bool num_neg = num < ZeroDuration();
+  const bool den_neg = den < ZeroDuration();
+  const bool quotient_neg = num_neg != den_neg;
+
+  if (time_internal::IsInfiniteDuration(num) || den == ZeroDuration()) {
+    *rem = num_neg ? -InfiniteDuration() : InfiniteDuration();
+    return quotient_neg ? kint64min : kint64max;
+  }
+  if (time_internal::IsInfiniteDuration(den)) {
+    *rem = num;
+    return 0;
+  }
+
+  const uint128 a = MakeU128Ticks(num);
+  const uint128 b = MakeU128Ticks(den);
+  uint128 quotient128 = a / b;
+
+  if (satq) {
+    // Limits the quotient to the range of int64_t.
+    if (quotient128 > uint128(static_cast<uint64_t>(kint64max))) {
+      quotient128 = quotient_neg ? uint128(static_cast<uint64_t>(kint64min))
+                                 : uint128(static_cast<uint64_t>(kint64max));
+    }
+  }
+
+  const uint128 remainder128 = a - quotient128 * b;
+  *rem = MakeDurationFromU128(remainder128, num_neg);
+
+  if (!quotient_neg || quotient128 == 0) {
+    return Uint128Low64(quotient128) & kint64max;
+  }
+  // The quotient needs to be negated, but we need to carefully handle
+  // quotient128s with the top bit on.
+  return -static_cast<int64_t>(Uint128Low64(quotient128 - 1) & kint64max) - 1;
+}
+
+}  // namespace time_internal
+
+//
+// Additive operators.
+//
+
+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_;
+  rep_hi_ =
+      DecodeTwosComp(EncodeTwosComp(rep_hi_) + EncodeTwosComp(rhs.rep_hi_));
+  if (rep_lo_ >= kTicksPerSecond - rhs.rep_lo_) {
+    rep_hi_ = DecodeTwosComp(EncodeTwosComp(rep_hi_) + 1);
+    rep_lo_ -= kTicksPerSecond;
+  }
+  rep_lo_ += rhs.rep_lo_;
+  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;
+}
+
+Duration& Duration::operator-=(Duration rhs) {
+  if (time_internal::IsInfiniteDuration(*this)) return *this;
+  if (time_internal::IsInfiniteDuration(rhs)) {
+    return *this = rhs.rep_hi_ >= 0 ? -InfiniteDuration() : InfiniteDuration();
+  }
+  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_) - 1);
+    rep_lo_ += kTicksPerSecond;
+  }
+  rep_lo_ -= rhs.rep_lo_;
+  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;
+}
+
+//
+// Multiplicative operators.
+//
+
+Duration& Duration::operator*=(int64_t r) {
+  if (time_internal::IsInfiniteDuration(*this)) {
+    const bool is_neg = (r < 0) != (rep_hi_ < 0);
+    return *this = is_neg ? -InfiniteDuration() : InfiniteDuration();
+  }
+  return *this = ScaleFixed<SafeMultiply>(*this, r);
+}
+
+Duration& Duration::operator*=(double r) {
+  if (time_internal::IsInfiniteDuration(*this) || !IsFinite(r)) {
+    const bool is_neg = (std::signbit(r) != 0) != (rep_hi_ < 0);
+    return *this = is_neg ? -InfiniteDuration() : InfiniteDuration();
+  }
+  return *this = ScaleDouble<std::multiplies>(*this, r);
+}
+
+Duration& Duration::operator/=(int64_t r) {
+  if (time_internal::IsInfiniteDuration(*this) || r == 0) {
+    const bool is_neg = (r < 0) != (rep_hi_ < 0);
+    return *this = is_neg ? -InfiniteDuration() : InfiniteDuration();
+  }
+  return *this = ScaleFixed<std::divides>(*this, r);
+}
+
+Duration& Duration::operator/=(double r) {
+  if (time_internal::IsInfiniteDuration(*this) || !IsValidDivisor(r)) {
+    const bool is_neg = (std::signbit(r) != 0) != (rep_hi_ < 0);
+    return *this = is_neg ? -InfiniteDuration() : InfiniteDuration();
+  }
+  return *this = ScaleDouble<std::divides>(*this, r);
+}
+
+Duration& Duration::operator%=(Duration rhs) {
+  time_internal::IDivDuration(false, *this, rhs, this);
+  return *this;
+}
+
+double FDivDuration(Duration num, Duration den) {
+  // Arithmetic with infinity is sticky.
+  if (time_internal::IsInfiniteDuration(num) || den == ZeroDuration()) {
+    return (num < ZeroDuration()) == (den < ZeroDuration())
+               ? std::numeric_limits<double>::infinity()
+               : -std::numeric_limits<double>::infinity();
+  }
+  if (time_internal::IsInfiniteDuration(den)) return 0.0;
+
+  double a =
+      static_cast<double>(time_internal::GetRepHi(num)) * kTicksPerSecond +
+      time_internal::GetRepLo(num);
+  double b =
+      static_cast<double>(time_internal::GetRepHi(den)) * kTicksPerSecond +
+      time_internal::GetRepLo(den);
+  return a / b;
+}
+
+//
+// Trunc/Floor/Ceil.
+//
+
+Duration Trunc(Duration d, Duration unit) {
+  return d - (d % unit);
+}
+
+Duration Floor(const Duration d, const Duration unit) {
+  const absl::Duration td = Trunc(d, unit);
+  return td <= d ? td : td - AbsDuration(unit);
+}
+
+Duration Ceil(const Duration d, const Duration unit) {
+  const absl::Duration td = Trunc(d, unit);
+  return td >= d ? td : td + AbsDuration(unit);
+}
+
+//
+// Factory functions.
+//
+
+Duration DurationFromTimespec(timespec ts) {
+  if (static_cast<uint64_t>(ts.tv_nsec) < 1000 * 1000 * 1000) {
+    int64_t ticks = ts.tv_nsec * kTicksPerNanosecond;
+    return time_internal::MakeDuration(ts.tv_sec, ticks);
+  }
+  return Seconds(ts.tv_sec) + Nanoseconds(ts.tv_nsec);
+}
+
+Duration DurationFromTimeval(timeval tv) {
+  if (static_cast<uint64_t>(tv.tv_usec) < 1000 * 1000) {
+    int64_t ticks = tv.tv_usec * 1000 * kTicksPerNanosecond;
+    return time_internal::MakeDuration(tv.tv_sec, ticks);
+  }
+  return Seconds(tv.tv_sec) + Microseconds(tv.tv_usec);
+}
+
+//
+// Conversion to other duration types.
+//
+
+int64_t ToInt64Nanoseconds(Duration d) {
+  if (time_internal::GetRepHi(d) >= 0 &&
+      time_internal::GetRepHi(d) >> 33 == 0) {
+    return (time_internal::GetRepHi(d) * 1000 * 1000 * 1000) +
+           (time_internal::GetRepLo(d) / kTicksPerNanosecond);
+  }
+  return d / Nanoseconds(1);
+}
+int64_t ToInt64Microseconds(Duration d) {
+  if (time_internal::GetRepHi(d) >= 0 &&
+      time_internal::GetRepHi(d) >> 43 == 0) {
+    return (time_internal::GetRepHi(d) * 1000 * 1000) +
+           (time_internal::GetRepLo(d) / (kTicksPerNanosecond * 1000));
+  }
+  return d / Microseconds(1);
+}
+int64_t ToInt64Milliseconds(Duration d) {
+  if (time_internal::GetRepHi(d) >= 0 &&
+      time_internal::GetRepHi(d) >> 53 == 0) {
+    return (time_internal::GetRepHi(d) * 1000) +
+           (time_internal::GetRepLo(d) / (kTicksPerNanosecond * 1000 * 1000));
+  }
+  return d / Milliseconds(1);
+}
+int64_t ToInt64Seconds(Duration d) {
+  int64_t hi = time_internal::GetRepHi(d);
+  if (time_internal::IsInfiniteDuration(d)) return hi;
+  if (hi < 0 && time_internal::GetRepLo(d) != 0) ++hi;
+  return hi;
+}
+int64_t ToInt64Minutes(Duration d) {
+  int64_t hi = time_internal::GetRepHi(d);
+  if (time_internal::IsInfiniteDuration(d)) return hi;
+  if (hi < 0 && time_internal::GetRepLo(d) != 0) ++hi;
+  return hi / 60;
+}
+int64_t ToInt64Hours(Duration d) {
+  int64_t hi = time_internal::GetRepHi(d);
+  if (time_internal::IsInfiniteDuration(d)) return hi;
+  if (hi < 0 && time_internal::GetRepLo(d) != 0) ++hi;
+  return hi / (60 * 60);
+}
+
+double ToDoubleNanoseconds(Duration d) {
+  return FDivDuration(d, Nanoseconds(1));
+}
+double ToDoubleMicroseconds(Duration d) {
+  return FDivDuration(d, Microseconds(1));
+}
+double ToDoubleMilliseconds(Duration d) {
+  return FDivDuration(d, Milliseconds(1));
+}
+double ToDoubleSeconds(Duration d) {
+  return FDivDuration(d, Seconds(1));
+}
+double ToDoubleMinutes(Duration d) {
+  return FDivDuration(d, Minutes(1));
+}
+double ToDoubleHours(Duration d) {
+  return FDivDuration(d, Hours(1));
+}
+
+timespec ToTimespec(Duration d) {
+  timespec ts;
+  if (!time_internal::IsInfiniteDuration(d)) {
+    int64_t rep_hi = time_internal::GetRepHi(d);
+    uint32_t rep_lo = time_internal::GetRepLo(d);
+    if (rep_hi < 0) {
+      // Tweak the fields so that unsigned division of rep_lo
+      // maps to truncation (towards zero) for the timespec.
+      rep_lo += kTicksPerNanosecond - 1;
+      if (rep_lo >= kTicksPerSecond) {
+        rep_hi += 1;
+        rep_lo -= kTicksPerSecond;
+      }
+    }
+    ts.tv_sec = rep_hi;
+    if (ts.tv_sec == rep_hi) {  // no time_t narrowing
+      ts.tv_nsec = rep_lo / kTicksPerNanosecond;
+      return ts;
+    }
+  }
+  if (d >= ZeroDuration()) {
+    ts.tv_sec = std::numeric_limits<time_t>::max();
+    ts.tv_nsec = 1000 * 1000 * 1000 - 1;
+  } else {
+    ts.tv_sec = std::numeric_limits<time_t>::min();
+    ts.tv_nsec = 0;
+  }
+  return ts;
+}
+
+timeval ToTimeval(Duration d) {
+  timeval tv;
+  timespec ts = ToTimespec(d);
+  if (ts.tv_sec < 0) {
+    // Tweak the fields so that positive division of tv_nsec
+    // maps to truncation (towards zero) for the timeval.
+    ts.tv_nsec += 1000 - 1;
+    if (ts.tv_nsec >= 1000 * 1000 * 1000) {
+      ts.tv_sec += 1;
+      ts.tv_nsec -= 1000 * 1000 * 1000;
+    }
+  }
+  tv.tv_sec = ts.tv_sec;
+  if (tv.tv_sec != ts.tv_sec) {  // narrowing
+    if (ts.tv_sec < 0) {
+      tv.tv_sec = std::numeric_limits<decltype(tv.tv_sec)>::min();
+      tv.tv_usec = 0;
+    } else {
+      tv.tv_sec = std::numeric_limits<decltype(tv.tv_sec)>::max();
+      tv.tv_usec = 1000 * 1000 - 1;
+    }
+    return tv;
+  }
+  tv.tv_usec = static_cast<int>(ts.tv_nsec / 1000);  // suseconds_t
+  return tv;
+}
+
+std::chrono::nanoseconds ToChronoNanoseconds(Duration d) {
+  return time_internal::ToChronoDuration<std::chrono::nanoseconds>(d);
+}
+std::chrono::microseconds ToChronoMicroseconds(Duration d) {
+  return time_internal::ToChronoDuration<std::chrono::microseconds>(d);
+}
+std::chrono::milliseconds ToChronoMilliseconds(Duration d) {
+  return time_internal::ToChronoDuration<std::chrono::milliseconds>(d);
+}
+std::chrono::seconds ToChronoSeconds(Duration d) {
+  return time_internal::ToChronoDuration<std::chrono::seconds>(d);
+}
+std::chrono::minutes ToChronoMinutes(Duration d) {
+  return time_internal::ToChronoDuration<std::chrono::minutes>(d);
+}
+std::chrono::hours ToChronoHours(Duration d) {
+  return time_internal::ToChronoDuration<std::chrono::hours>(d);
+}
+
+//
+// To/From string formatting.
+//
+
+namespace {
+
+// Formats a positive 64-bit integer in the given field width.  Note that
+// it is up to the caller of Format64() to ensure that there is sufficient
+// space before ep to hold the conversion.
+char* Format64(char* ep, int width, int64_t v) {
+  do {
+    --width;
+    *--ep = '0' + (v % 10);  // contiguous digits
+  } while (v /= 10);
+  while (--width >= 0) *--ep = '0';  // zero pad
+  return ep;
+}
+
+// Helpers for FormatDuration() that format 'n' and append it to 'out'
+// followed by the given 'unit'.  If 'n' formats to "0", nothing is
+// appended (not even the unit).
+
+// A type that encapsulates how to display a value of a particular unit. For
+// values that are displayed with fractional parts, the precision indicates
+// where to round the value. The precision varies with the display unit because
+// a Duration can hold only quarters of a nanosecond, so displaying information
+// beyond that is just noise.
+//
+// For example, a microsecond value of 42.00025xxxxx should not display beyond 5
+// fractional digits, because it is in the noise of what a Duration can
+// represent.
+struct DisplayUnit {
+  const char* abbr;
+  int prec;
+  double pow10;
+};
+const DisplayUnit kDisplayNano = {"ns", 2, 1e2};
+const DisplayUnit kDisplayMicro = {"us", 5, 1e5};
+const DisplayUnit kDisplayMilli = {"ms", 8, 1e8};
+const DisplayUnit kDisplaySec = {"s", 11, 1e11};
+const DisplayUnit kDisplayMin = {"m", -1, 0.0};   // prec ignored
+const DisplayUnit kDisplayHour = {"h", -1, 0.0};  // prec ignored
+
+void AppendNumberUnit(std::string* out, int64_t n, DisplayUnit unit) {
+  char buf[sizeof("2562047788015216")];  // hours in max duration
+  char* const ep = buf + sizeof(buf);
+  char* bp = Format64(ep, 0, n);
+  if (*bp != '0' || bp + 1 != ep) {
+    out->append(bp, ep - bp);
+    out->append(unit.abbr);
+  }
+}
+
+// Note: unit.prec is limited to double's digits10 value (typically 15) so it
+// always fits in buf[].
+void AppendNumberUnit(std::string* out, double n, DisplayUnit unit) {
+  constexpr int kBufferSize = std::numeric_limits<double>::digits10;
+  const int prec = std::min(kBufferSize, unit.prec);
+  char buf[kBufferSize];  // also large enough to hold integer part
+  char* ep = buf + sizeof(buf);
+  double d = 0;
+  int64_t frac_part = Round(std::modf(n, &d) * unit.pow10);
+  int64_t int_part = d;
+  if (int_part != 0 || frac_part != 0) {
+    char* bp = Format64(ep, 0, int_part);  // always < 1000
+    out->append(bp, ep - bp);
+    if (frac_part != 0) {
+      out->push_back('.');
+      bp = Format64(ep, prec, frac_part);
+      while (ep[-1] == '0') --ep;
+      out->append(bp, ep - bp);
+    }
+    out->append(unit.abbr);
+  }
+}
+
+}  // namespace
+
+// From Go's doc at https://golang.org/pkg/time/#Duration.String
+//   [FormatDuration] returns a string representing the duration in the
+//   form "72h3m0.5s". Leading zero units are omitted.  As a special
+//   case, durations less than one second format use a smaller unit
+//   (milli-, micro-, or nanoseconds) to ensure that the leading digit
+//   is non-zero.  The zero duration formats as 0, with no unit.
+std::string FormatDuration(Duration d) {
+  const Duration min_duration = Seconds(kint64min);
+  if (d == min_duration) {
+    // Avoid needing to negate kint64min by directly returning what the
+    // following code should produce in that case.
+    return "-2562047788015215h30m8s";
+  }
+  std::string s;
+  if (d < ZeroDuration()) {
+    s.append("-");
+    d = -d;
+  }
+  if (d == InfiniteDuration()) {
+    s.append("inf");
+  } else if (d < Seconds(1)) {
+    // Special case for durations with a magnitude < 1 second.  The duration
+    // is printed as a fraction of a single unit, e.g., "1.2ms".
+    if (d < Microseconds(1)) {
+      AppendNumberUnit(&s, FDivDuration(d, Nanoseconds(1)), kDisplayNano);
+    } else if (d < Milliseconds(1)) {
+      AppendNumberUnit(&s, FDivDuration(d, Microseconds(1)), kDisplayMicro);
+    } else {
+      AppendNumberUnit(&s, FDivDuration(d, Milliseconds(1)), kDisplayMilli);
+    }
+  } else {
+    AppendNumberUnit(&s, IDivDuration(d, Hours(1), &d), kDisplayHour);
+    AppendNumberUnit(&s, IDivDuration(d, Minutes(1), &d), kDisplayMin);
+    AppendNumberUnit(&s, FDivDuration(d, Seconds(1)), kDisplaySec);
+  }
+  if (s.empty() || s == "-") {
+    s = "0";
+  }
+  return s;
+}
+
+namespace {
+
+// A helper for ParseDuration() that parses a leading number from the given
+// string and stores the result in *int_part/*frac_part/*frac_scale.  The
+// given string pointer is modified to point to the first unconsumed char.
+bool ConsumeDurationNumber(const char** dpp, const char* ep, int64_t* int_part,
+                           int64_t* frac_part, int64_t* frac_scale) {
+  *int_part = 0;
+  *frac_part = 0;
+  *frac_scale = 1;  // invariant: *frac_part < *frac_scale
+  const char* start = *dpp;
+  for (; *dpp != ep; *dpp += 1) {
+    const int d = **dpp - '0';  // contiguous digits
+    if (d < 0 || 10 <= d) break;
+
+    if (*int_part > kint64max / 10) return false;
+    *int_part *= 10;
+    if (*int_part > kint64max - d) return false;
+    *int_part += d;
+  }
+  const bool int_part_empty = (*dpp == start);
+  if (*dpp == ep || **dpp != '.') return !int_part_empty;
+
+  for (*dpp += 1; *dpp != ep; *dpp += 1) {
+    const int d = **dpp - '0';  // contiguous digits
+    if (d < 0 || 10 <= d) break;
+    if (*frac_scale <= kint64max / 10) {
+      *frac_part *= 10;
+      *frac_part += d;
+      *frac_scale *= 10;
+    }
+  }
+  return !int_part_empty || *frac_scale != 1;
+}
+
+// A helper for ParseDuration() that parses a leading unit designator (e.g.,
+// ns, us, ms, s, m, h) from the given string and stores the resulting unit
+// in "*unit".  The given string pointer is modified to point to the first
+// unconsumed char.
+bool ConsumeDurationUnit(const char** start, const char* end, Duration* unit) {
+  size_t size = end - *start;
+  switch (size) {
+    case 0:
+      return false;
+    default:
+      switch (**start) {
+        case 'n':
+          if (*(*start + 1) == 's') {
+            *start += 2;
+            *unit = Nanoseconds(1);
+            return true;
+          }
+          break;
+        case 'u':
+          if (*(*start + 1) == 's') {
+            *start += 2;
+            *unit = Microseconds(1);
+            return true;
+          }
+          break;
+        case 'm':
+          if (*(*start + 1) == 's') {
+            *start += 2;
+            *unit = Milliseconds(1);
+            return true;
+          }
+          break;
+        default:
+          break;
+      }
+      ABSL_FALLTHROUGH_INTENDED;
+    case 1:
+      switch (**start) {
+        case 's':
+          *unit = Seconds(1);
+          *start += 1;
+          return true;
+        case 'm':
+          *unit = Minutes(1);
+          *start += 1;
+          return true;
+        case 'h':
+          *unit = Hours(1);
+          *start += 1;
+          return true;
+        default:
+          return false;
+      }
+  }
+}
+
+}  // namespace
+
+// From Go's doc at https://golang.org/pkg/time/#ParseDuration
+//   [ParseDuration] parses a duration string. A duration string is
+//   a possibly signed sequence of decimal numbers, each with optional
+//   fraction and a unit suffix, such as "300ms", "-1.5h" or "2h45m".
+//   Valid time units are "ns", "us" "ms", "s", "m", "h".
+bool ParseDuration(absl::string_view dur_sv, Duration* d) {
+  int sign = 1;
+  if (absl::ConsumePrefix(&dur_sv, "-")) {
+    sign = -1;
+  } else {
+    absl::ConsumePrefix(&dur_sv, "+");
+  }
+  if (dur_sv.empty()) return false;
+
+  // Special case for a string of "0".
+  if (dur_sv == "0") {
+    *d = ZeroDuration();
+    return true;
+  }
+
+  if (dur_sv == "inf") {
+    *d = sign * InfiniteDuration();
+    return true;
+  }
+
+  const char* start = dur_sv.data();
+  const char* end = start + dur_sv.size();
+
+  Duration dur;
+  while (start != end) {
+    int64_t int_part;
+    int64_t frac_part;
+    int64_t frac_scale;
+    Duration unit;
+    if (!ConsumeDurationNumber(&start, end, &int_part, &frac_part,
+                               &frac_scale) ||
+        !ConsumeDurationUnit(&start, end, &unit)) {
+      return false;
+    }
+    if (int_part != 0) dur += sign * int_part * unit;
+    if (frac_part != 0) dur += sign * frac_part * unit / frac_scale;
+  }
+  *d = dur;
+  return true;
+}
+
+bool AbslParseFlag(absl::string_view text, Duration* dst, std::string*) {
+  return ParseDuration(text, dst);
+}
+
+std::string AbslUnparseFlag(Duration d) { return FormatDuration(d); }
+bool ParseFlag(const std::string& text, Duration* dst, std::string* ) {
+  return ParseDuration(text, dst);
+}
+
+std::string UnparseFlag(Duration d) { return FormatDuration(d); }
+
+ABSL_NAMESPACE_END
+}  // namespace absl