Export of internal Abseil changes.

--
7a6ff16a85beb730c172d5d25cf1b5e1be885c56 by Laramie Leavitt <lar@google.com>:

Internal change.

PiperOrigin-RevId: 254454546

--
ff8f9bafaefc26d451f576ea4a06d150aed63f6f by Andy Soffer <asoffer@google.com>:

Internal changes

PiperOrigin-RevId: 254451562

--
deefc5b651b479ce36f0b4ef203e119c0c8936f2 by CJ Johnson <johnsoncj@google.com>:

Account for subtracting unsigned values from the size of InlinedVector

PiperOrigin-RevId: 254450625

--
3c677316a27bcadc17e41957c809ca472d5fef14 by Andy Soffer <asoffer@google.com>:

Add C++17's std::make_from_tuple to absl/utility/utility.h

PiperOrigin-RevId: 254411573

--
4ee3536a918830eeec402a28fc31a62c7c90b940 by CJ Johnson <johnsoncj@google.com>:

Adds benchmark for the rest of the InlinedVector public API

PiperOrigin-RevId: 254408378

--
e5a21a00700ee83498ff1efbf649169756463ee4 by CJ Johnson <johnsoncj@google.com>:

Updates the definition of InlinedVector::shrink_to_fit() to be exception safe and adds exception safety tests for it.

PiperOrigin-RevId: 254401387

--
2ea82e72b86d82d78b4e4712a63a55981b53c64b by Laramie Leavitt <lar@google.com>:

Use absl::InsecureBitGen in place of std::mt19937
in tests absl/random/...distribution_test.cc

PiperOrigin-RevId: 254289444

--
fa099e02c413a7ffda732415e8105cad26a90337 by Andy Soffer <asoffer@google.com>:

Internal changes

PiperOrigin-RevId: 254286334

--
ce34b7f36933b30cfa35b9c9a5697a792b5666e4 by Andy Soffer <asoffer@google.com>:

Internal changes

PiperOrigin-RevId: 254273059

--
6f9c473da7c2090c2e85a37c5f00622e8a912a89 by Jorg Brown <jorg@google.com>:

Change absl::container_internal::CompressedTuple to instantiate its
internal Storage class with the name of the type it's holding, rather
than the name of the Tuple.  This is not an externally-visible change,
other than less compiler memory is used and less debug information is
generated.

PiperOrigin-RevId: 254269285

--
8bd3c186bf2fc0c55d8a2dd6f28a5327502c9fba by Andy Soffer <asoffer@google.com>:

Adding short-hand IntervalClosed for IntervalClosedClosed and IntervalOpen for
IntervalOpenOpen.

PiperOrigin-RevId: 254252419

--
ea957f99b6a04fccd42aa05605605f3b44b1ecfd by Abseil Team <absl-team@google.com>:

Do not directly use __SIZEOF_INT128__.

In order to avoid linker errors when building with clang-cl (__fixunsdfti, __udivti3 and __fixunssfti are undefined), this CL uses ABSL_HAVE_INTRINSIC_INT128 which is not defined for clang-cl.

PiperOrigin-RevId: 254250739

--
89ab385cd26b34d64130bce856253aaba96d2345 by Andy Soffer <asoffer@google.com>:

Internal changes

PiperOrigin-RevId: 254242321

--
cffc793d93eca6d6bdf7de733847b6ab4a255ae9 by CJ Johnson <johnsoncj@google.com>:

Adds benchmark for InlinedVector::reserve(size_type)

PiperOrigin-RevId: 254199226

--
c90c7a9fa3c8f0c9d5114036979548b055ea2f2a by Gennadiy Rozental <rogeeff@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 254072387

--
c4c388beae016c9570ab54ffa1d52660e4a85b7b by Laramie Leavitt <lar@google.com>:

Internal cleanup.

PiperOrigin-RevId: 254062381

--
d3c992e221cc74e5372d0c8fa410170b6a43c062 by Tom Manshreck <shreck@google.com>:

Update distributions.h to Abseil standards

PiperOrigin-RevId: 254054946

--
d15ad0035c34ef11b14fadc5a4a2d3ec415f5518 by CJ Johnson <johnsoncj@google.com>:

Removes functions with only one caller from the implementation details of InlinedVector by manually inlining the definitions

PiperOrigin-RevId: 254005427

--
2f37e807efc3a8ef1f4b539bdd379917d4151520 by Andy Soffer <asoffer@google.com>:

Initial release of Abseil Random

PiperOrigin-RevId: 253999861

--
24ed1694b6430791d781ed533a8f8ccf6cac5856 by CJ Johnson <johnsoncj@google.com>:

Updates the definition of InlinedVector::assign(...)/InlinedVector::operator=(...) to new, exception-safe implementations with exception safety tests to boot

PiperOrigin-RevId: 253993691

--
5613d95f5a7e34a535cfaeadce801441e990843e by CJ Johnson <johnsoncj@google.com>:

Adds benchmarks for InlinedVector::shrink_to_fit()

PiperOrigin-RevId: 253989647

--
2a96ddfdac40bbb8cb6a7f1aeab90917067c6e63 by Abseil Team <absl-team@google.com>:

Initial release of Abseil Random

PiperOrigin-RevId: 253927497

--
bf1aff8fc9ffa921ad74643e9525ecf25b0d8dc1 by Andy Soffer <asoffer@google.com>:

Initial release of Abseil Random

PiperOrigin-RevId: 253920512

--
bfc03f4a3dcda3cf3a4b84bdb84cda24e3394f41 by Laramie Leavitt <lar@google.com>:

Internal change.

PiperOrigin-RevId: 253886486

--
05036cfcc078ca7c5f581a00dfb0daed568cbb69 by Eric Fiselier <ericwf@google.com>:

Don't include `winsock2.h` because it drags in `windows.h` and friends,
and they define awful macros like OPAQUE, ERROR, and more. This has the
potential to break abseil users.

Instead we only forward declare `timeval` and require Windows users
include `winsock2.h` themselves. This is both inconsistent and poor QoI, but so
including 'windows.h' is bad too.

PiperOrigin-RevId: 253852615
GitOrigin-RevId: 7a6ff16a85beb730c172d5d25cf1b5e1be885c56
Change-Id: Icd6aff87da26f29ec8915da856f051129987cef6

1 files changed, 506 insertions, 0 deletions

diff --git a/absl/random/internal/distribution_impl_test.cc b/absl/random/internal/distribution_impl_test.cc
new file mode 100644
index 000000000000..09e7a318ccc5
--- /dev/null
+++ b/absl/random/internal/distribution_impl_test.cc
@@ -0,0 +1,506 @@
+// 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.
+
+#include "absl/random/internal/distribution_impl.h"
+
+#include "gtest/gtest.h"
+#include "absl/base/internal/bits.h"
+#include "absl/flags/flag.h"
+#include "absl/numeric/int128.h"
+
+ABSL_FLAG(int64_t, absl_random_test_trials, 50000,
+          "Number of trials for the probability tests.");
+
+using absl::random_internal::NegativeValueT;
+using absl::random_internal::PositiveValueT;
+using absl::random_internal::RandU64ToDouble;
+using absl::random_internal::RandU64ToFloat;
+using absl::random_internal::SignedValueT;
+
+namespace {
+
+TEST(DistributionImplTest, U64ToFloat_Positive_NoZero_Test) {
+  auto ToFloat = [](uint64_t a) {
+    return RandU64ToFloat<PositiveValueT, false>(a);
+  };
+  EXPECT_EQ(ToFloat(0x0000000000000000), 2.710505431e-20f);
+  EXPECT_EQ(ToFloat(0x0000000000000001), 5.421010862e-20f);
+  EXPECT_EQ(ToFloat(0x8000000000000000), 0.5);
+  EXPECT_EQ(ToFloat(0xFFFFFFFFFFFFFFFF), 0.9999999404f);
+}
+
+TEST(DistributionImplTest, U64ToFloat_Positive_Zero_Test) {
+  auto ToFloat = [](uint64_t a) {
+    return RandU64ToFloat<PositiveValueT, true>(a);
+  };
+  EXPECT_EQ(ToFloat(0x0000000000000000), 0.0);
+  EXPECT_EQ(ToFloat(0x0000000000000001), 5.421010862e-20f);
+  EXPECT_EQ(ToFloat(0x8000000000000000), 0.5);
+  EXPECT_EQ(ToFloat(0xFFFFFFFFFFFFFFFF), 0.9999999404f);
+}
+
+TEST(DistributionImplTest, U64ToFloat_Negative_NoZero_Test) {
+  auto ToFloat = [](uint64_t a) {
+    return RandU64ToFloat<NegativeValueT, false>(a);
+  };
+  EXPECT_EQ(ToFloat(0x0000000000000000), -2.710505431e-20f);
+  EXPECT_EQ(ToFloat(0x0000000000000001), -5.421010862e-20f);
+  EXPECT_EQ(ToFloat(0x8000000000000000), -0.5);
+  EXPECT_EQ(ToFloat(0xFFFFFFFFFFFFFFFF), -0.9999999404f);
+}
+
+TEST(DistributionImplTest, U64ToFloat_Signed_NoZero_Test) {
+  auto ToFloat = [](uint64_t a) {
+    return RandU64ToFloat<SignedValueT, false>(a);
+  };
+  EXPECT_EQ(ToFloat(0x0000000000000000), 5.421010862e-20f);
+  EXPECT_EQ(ToFloat(0x0000000000000001), 1.084202172e-19f);
+  EXPECT_EQ(ToFloat(0x7FFFFFFFFFFFFFFF), 0.9999999404f);
+  EXPECT_EQ(ToFloat(0x8000000000000000), -5.421010862e-20f);
+  EXPECT_EQ(ToFloat(0x8000000000000001), -1.084202172e-19f);
+  EXPECT_EQ(ToFloat(0xFFFFFFFFFFFFFFFF), -0.9999999404f);
+}
+
+TEST(DistributionImplTest, U64ToFloat_Signed_Zero_Test) {
+  auto ToFloat = [](uint64_t a) {
+    return RandU64ToFloat<SignedValueT, true>(a);
+  };
+  EXPECT_EQ(ToFloat(0x0000000000000000), 0);
+  EXPECT_EQ(ToFloat(0x0000000000000001), 1.084202172e-19f);
+  EXPECT_EQ(ToFloat(0x7FFFFFFFFFFFFFFF), 0.9999999404f);
+  EXPECT_EQ(ToFloat(0x8000000000000000), 0);
+  EXPECT_EQ(ToFloat(0x8000000000000001), -1.084202172e-19f);
+  EXPECT_EQ(ToFloat(0xFFFFFFFFFFFFFFFF), -0.9999999404f);
+}
+
+TEST(DistributionImplTest, U64ToFloat_Signed_Bias_Test) {
+  auto ToFloat = [](uint64_t a) {
+    return RandU64ToFloat<SignedValueT, true, 1>(a);
+  };
+  EXPECT_EQ(ToFloat(0x0000000000000000), 0);
+  EXPECT_EQ(ToFloat(0x0000000000000001), 2 * 1.084202172e-19f);
+  EXPECT_EQ(ToFloat(0x7FFFFFFFFFFFFFFF), 2 * 0.9999999404f);
+  EXPECT_EQ(ToFloat(0x8000000000000000), 0);
+  EXPECT_EQ(ToFloat(0x8000000000000001), 2 * -1.084202172e-19f);
+  EXPECT_EQ(ToFloat(0xFFFFFFFFFFFFFFFF), 2 * -0.9999999404f);
+}
+
+TEST(DistributionImplTest, U64ToFloatTest) {
+  auto ToFloat = [](uint64_t a) -> float {
+    return RandU64ToFloat<PositiveValueT, true>(a);
+  };
+
+  EXPECT_EQ(ToFloat(0x0000000000000000), 0.0f);
+
+  EXPECT_EQ(ToFloat(0x8000000000000000), 0.5f);
+  EXPECT_EQ(ToFloat(0x8000000000000001), 0.5f);
+  EXPECT_EQ(ToFloat(0x800000FFFFFFFFFF), 0.5f);
+  EXPECT_EQ(ToFloat(0xFFFFFFFFFFFFFFFF), 0.9999999404f);
+
+  EXPECT_GT(ToFloat(0x0000000000000001), 0.0f);
+
+  EXPECT_NE(ToFloat(0x7FFFFF0000000000), ToFloat(0x7FFFFEFFFFFFFFFF));
+
+  EXPECT_LT(ToFloat(0xFFFFFFFFFFFFFFFF), 1.0f);
+  int32_t two_to_24 = 1 << 24;
+  EXPECT_EQ(static_cast<int32_t>(ToFloat(0xFFFFFFFFFFFFFFFF) * two_to_24),
+            two_to_24 - 1);
+  EXPECT_NE(static_cast<int32_t>(ToFloat(0xFFFFFFFFFFFFFFFF) * two_to_24 * 2),
+            two_to_24 * 2 - 1);
+  EXPECT_EQ(ToFloat(0xFFFFFFFFFFFFFFFF), ToFloat(0xFFFFFF0000000000));
+  EXPECT_NE(ToFloat(0xFFFFFFFFFFFFFFFF), ToFloat(0xFFFFFEFFFFFFFFFF));
+  EXPECT_EQ(ToFloat(0x7FFFFFFFFFFFFFFF), ToFloat(0x7FFFFF8000000000));
+  EXPECT_NE(ToFloat(0x7FFFFFFFFFFFFFFF), ToFloat(0x7FFFFF7FFFFFFFFF));
+  EXPECT_EQ(ToFloat(0x3FFFFFFFFFFFFFFF), ToFloat(0x3FFFFFC000000000));
+  EXPECT_NE(ToFloat(0x3FFFFFFFFFFFFFFF), ToFloat(0x3FFFFFBFFFFFFFFF));
+
+  // For values where every bit counts, the values scale as multiples of the
+  // input.
+  for (int i = 0; i < 100; ++i) {
+    EXPECT_EQ(i * ToFloat(0x0000000000000001), ToFloat(i));
+  }
+
+  // For each i: value generated from (1 << i).
+  float exp_values[64];
+  exp_values[63] = 0.5f;
+  for (int i = 62; i >= 0; --i) exp_values[i] = 0.5f * exp_values[i + 1];
+  constexpr uint64_t one = 1;
+  for (int i = 0; i < 64; ++i) {
+    EXPECT_EQ(ToFloat(one << i), exp_values[i]);
+    for (int j = 1; j < FLT_MANT_DIG && i - j >= 0; ++j) {
+      EXPECT_NE(exp_values[i] + exp_values[i - j], exp_values[i]);
+      EXPECT_EQ(ToFloat((one << i) + (one << (i - j))),
+                exp_values[i] + exp_values[i - j]);
+    }
+    for (int j = FLT_MANT_DIG; i - j >= 0; ++j) {
+      EXPECT_EQ(exp_values[i] + exp_values[i - j], exp_values[i]);
+      EXPECT_EQ(ToFloat((one << i) + (one << (i - j))), exp_values[i]);
+    }
+  }
+}
+
+TEST(DistributionImplTest, U64ToDouble_Positive_NoZero_Test) {
+  auto ToDouble = [](uint64_t a) {
+    return RandU64ToDouble<PositiveValueT, false>(a);
+  };
+
+  EXPECT_EQ(ToDouble(0x0000000000000000), 2.710505431213761085e-20);
+  EXPECT_EQ(ToDouble(0x0000000000000001), 5.42101086242752217004e-20);
+  EXPECT_EQ(ToDouble(0x0000000000000002), 1.084202172485504434e-19);
+  EXPECT_EQ(ToDouble(0x8000000000000000), 0.5);
+  EXPECT_EQ(ToDouble(0xFFFFFFFFFFFFFFFF), 0.999999999999999888978);
+}
+
+TEST(DistributionImplTest, U64ToDouble_Positive_Zero_Test) {
+  auto ToDouble = [](uint64_t a) {
+    return RandU64ToDouble<PositiveValueT, true>(a);
+  };
+
+  EXPECT_EQ(ToDouble(0x0000000000000000), 0.0);
+  EXPECT_EQ(ToDouble(0x0000000000000001), 5.42101086242752217004e-20);
+  EXPECT_EQ(ToDouble(0x8000000000000000), 0.5);
+  EXPECT_EQ(ToDouble(0xFFFFFFFFFFFFFFFF), 0.999999999999999888978);
+}
+
+TEST(DistributionImplTest, U64ToDouble_Negative_NoZero_Test) {
+  auto ToDouble = [](uint64_t a) {
+    return RandU64ToDouble<NegativeValueT, false>(a);
+  };
+
+  EXPECT_EQ(ToDouble(0x0000000000000000), -2.710505431213761085e-20);
+  EXPECT_EQ(ToDouble(0x0000000000000001), -5.42101086242752217004e-20);
+  EXPECT_EQ(ToDouble(0x0000000000000002), -1.084202172485504434e-19);
+  EXPECT_EQ(ToDouble(0x8000000000000000), -0.5);
+  EXPECT_EQ(ToDouble(0xFFFFFFFFFFFFFFFF), -0.999999999999999888978);
+}
+
+TEST(DistributionImplTest, U64ToDouble_Signed_NoZero_Test) {
+  auto ToDouble = [](uint64_t a) {
+    return RandU64ToDouble<SignedValueT, false>(a);
+  };
+
+  EXPECT_EQ(ToDouble(0x0000000000000000), 5.42101086242752217004e-20);
+  EXPECT_EQ(ToDouble(0x0000000000000001), 1.084202172485504434e-19);
+  EXPECT_EQ(ToDouble(0x7FFFFFFFFFFFFFFF), 0.999999999999999888978);
+  EXPECT_EQ(ToDouble(0x8000000000000000), -5.42101086242752217004e-20);
+  EXPECT_EQ(ToDouble(0x8000000000000001), -1.084202172485504434e-19);
+  EXPECT_EQ(ToDouble(0xFFFFFFFFFFFFFFFF), -0.999999999999999888978);
+}
+
+TEST(DistributionImplTest, U64ToDouble_Signed_Zero_Test) {
+  auto ToDouble = [](uint64_t a) {
+    return RandU64ToDouble<SignedValueT, true>(a);
+  };
+  EXPECT_EQ(ToDouble(0x0000000000000000), 0);
+  EXPECT_EQ(ToDouble(0x0000000000000001), 1.084202172485504434e-19);
+  EXPECT_EQ(ToDouble(0x7FFFFFFFFFFFFFFF), 0.999999999999999888978);
+  EXPECT_EQ(ToDouble(0x8000000000000000), 0);
+  EXPECT_EQ(ToDouble(0x8000000000000001), -1.084202172485504434e-19);
+  EXPECT_EQ(ToDouble(0xFFFFFFFFFFFFFFFF), -0.999999999999999888978);
+}
+
+TEST(DistributionImplTest, U64ToDouble_Signed_Bias_Test) {
+  auto ToDouble = [](uint64_t a) {
+    return RandU64ToDouble<SignedValueT, true, -1>(a);
+  };
+  EXPECT_EQ(ToDouble(0x0000000000000000), 0);
+  EXPECT_EQ(ToDouble(0x0000000000000001), 1.084202172485504434e-19 / 2);
+  EXPECT_EQ(ToDouble(0x7FFFFFFFFFFFFFFF), 0.999999999999999888978 / 2);
+  EXPECT_EQ(ToDouble(0x8000000000000000), 0);
+  EXPECT_EQ(ToDouble(0x8000000000000001), -1.084202172485504434e-19 / 2);
+  EXPECT_EQ(ToDouble(0xFFFFFFFFFFFFFFFF), -0.999999999999999888978 / 2);
+}
+
+TEST(DistributionImplTest, U64ToDoubleTest) {
+  auto ToDouble = [](uint64_t a) {
+    return RandU64ToDouble<PositiveValueT, true>(a);
+  };
+
+  EXPECT_EQ(ToDouble(0x0000000000000000), 0.0);
+  EXPECT_EQ(ToDouble(0x0000000000000000), 0.0);
+
+  EXPECT_EQ(ToDouble(0x0000000000000001), 5.42101086242752217004e-20);
+  EXPECT_EQ(ToDouble(0x7fffffffffffffef), 0.499999999999999944489);
+  EXPECT_EQ(ToDouble(0x8000000000000000), 0.5);
+
+  // For values > 0.5, RandU64ToDouble discards up to 11 bits. (64-53).
+  EXPECT_EQ(ToDouble(0x8000000000000001), 0.5);
+  EXPECT_EQ(ToDouble(0x80000000000007FF), 0.5);
+  EXPECT_EQ(ToDouble(0xFFFFFFFFFFFFFFFF), 0.999999999999999888978);
+  EXPECT_NE(ToDouble(0x7FFFFFFFFFFFF800), ToDouble(0x7FFFFFFFFFFFF7FF));
+
+  EXPECT_LT(ToDouble(0xFFFFFFFFFFFFFFFF), 1.0);
+  EXPECT_EQ(ToDouble(0xFFFFFFFFFFFFFFFF), ToDouble(0xFFFFFFFFFFFFF800));
+  EXPECT_NE(ToDouble(0xFFFFFFFFFFFFFFFF), ToDouble(0xFFFFFFFFFFFFF7FF));
+  EXPECT_EQ(ToDouble(0x7FFFFFFFFFFFFFFF), ToDouble(0x7FFFFFFFFFFFFC00));
+  EXPECT_NE(ToDouble(0x7FFFFFFFFFFFFFFF), ToDouble(0x7FFFFFFFFFFFFBFF));
+  EXPECT_EQ(ToDouble(0x3FFFFFFFFFFFFFFF), ToDouble(0x3FFFFFFFFFFFFE00));
+  EXPECT_NE(ToDouble(0x3FFFFFFFFFFFFFFF), ToDouble(0x3FFFFFFFFFFFFDFF));
+
+  EXPECT_EQ(ToDouble(0x1000000000000001), 0.0625);
+  EXPECT_EQ(ToDouble(0x2000000000000001), 0.125);
+  EXPECT_EQ(ToDouble(0x3000000000000001), 0.1875);
+  EXPECT_EQ(ToDouble(0x4000000000000001), 0.25);
+  EXPECT_EQ(ToDouble(0x5000000000000001), 0.3125);
+  EXPECT_EQ(ToDouble(0x6000000000000001), 0.375);
+  EXPECT_EQ(ToDouble(0x7000000000000001), 0.4375);
+  EXPECT_EQ(ToDouble(0x8000000000000001), 0.5);
+  EXPECT_EQ(ToDouble(0x9000000000000001), 0.5625);
+  EXPECT_EQ(ToDouble(0xa000000000000001), 0.625);
+  EXPECT_EQ(ToDouble(0xb000000000000001), 0.6875);
+  EXPECT_EQ(ToDouble(0xc000000000000001), 0.75);
+  EXPECT_EQ(ToDouble(0xd000000000000001), 0.8125);
+  EXPECT_EQ(ToDouble(0xe000000000000001), 0.875);
+  EXPECT_EQ(ToDouble(0xf000000000000001), 0.9375);
+
+  // Large powers of 2.
+  int64_t two_to_53 = int64_t{1} << 53;
+  EXPECT_EQ(static_cast<int64_t>(ToDouble(0xFFFFFFFFFFFFFFFF) * two_to_53),
+            two_to_53 - 1);
+  EXPECT_NE(static_cast<int64_t>(ToDouble(0xFFFFFFFFFFFFFFFF) * two_to_53 * 2),
+            two_to_53 * 2 - 1);
+
+  // For values where every bit counts, the values scale as multiples of the
+  // input.
+  for (int i = 0; i < 100; ++i) {
+    EXPECT_EQ(i * ToDouble(0x0000000000000001), ToDouble(i));
+  }
+
+  // For each i: value generated from (1 << i).
+  double exp_values[64];
+  exp_values[63] = 0.5;
+  for (int i = 62; i >= 0; --i) exp_values[i] = 0.5 * exp_values[i + 1];
+  constexpr uint64_t one = 1;
+  for (int i = 0; i < 64; ++i) {
+    EXPECT_EQ(ToDouble(one << i), exp_values[i]);
+    for (int j = 1; j < DBL_MANT_DIG && i - j >= 0; ++j) {
+      EXPECT_NE(exp_values[i] + exp_values[i - j], exp_values[i]);
+      EXPECT_EQ(ToDouble((one << i) + (one << (i - j))),
+                exp_values[i] + exp_values[i - j]);
+    }
+    for (int j = DBL_MANT_DIG; i - j >= 0; ++j) {
+      EXPECT_EQ(exp_values[i] + exp_values[i - j], exp_values[i]);
+      EXPECT_EQ(ToDouble((one << i) + (one << (i - j))), exp_values[i]);
+    }
+  }
+}
+
+TEST(DistributionImplTest, U64ToDoubleSignedTest) {
+  auto ToDouble = [](uint64_t a) {
+    return RandU64ToDouble<SignedValueT, false>(a);
+  };
+
+  EXPECT_EQ(ToDouble(0x0000000000000000), 5.42101086242752217004e-20);
+  EXPECT_EQ(ToDouble(0x0000000000000001), 1.084202172485504434e-19);
+
+  EXPECT_EQ(ToDouble(0x8000000000000000), -5.42101086242752217004e-20);
+  EXPECT_EQ(ToDouble(0x8000000000000001), -1.084202172485504434e-19);
+
+  const double e_plus = ToDouble(0x0000000000000001);
+  const double e_minus = ToDouble(0x8000000000000001);
+  EXPECT_EQ(e_plus, 1.084202172485504434e-19);
+  EXPECT_EQ(e_minus, -1.084202172485504434e-19);
+
+  EXPECT_EQ(ToDouble(0x3fffffffffffffef), 0.499999999999999944489);
+  EXPECT_EQ(ToDouble(0xbfffffffffffffef), -0.499999999999999944489);
+
+  // For values > 0.5, RandU64ToDouble discards up to 10 bits. (63-53).
+  EXPECT_EQ(ToDouble(0x4000000000000000), 0.5);
+  EXPECT_EQ(ToDouble(0x4000000000000001), 0.5);
+  EXPECT_EQ(ToDouble(0x40000000000003FF), 0.5);
+
+  EXPECT_EQ(ToDouble(0xC000000000000000), -0.5);
+  EXPECT_EQ(ToDouble(0xC000000000000001), -0.5);
+  EXPECT_EQ(ToDouble(0xC0000000000003FF), -0.5);
+
+  EXPECT_EQ(ToDouble(0x7FFFFFFFFFFFFFFe), 0.999999999999999888978);
+  EXPECT_EQ(ToDouble(0xFFFFFFFFFFFFFFFe), -0.999999999999999888978);
+
+  EXPECT_NE(ToDouble(0x7FFFFFFFFFFFF800), ToDouble(0x7FFFFFFFFFFFF7FF));
+
+  EXPECT_LT(ToDouble(0x7FFFFFFFFFFFFFFF), 1.0);
+  EXPECT_GT(ToDouble(0x7FFFFFFFFFFFFFFF), 0.9999999999);
+
+  EXPECT_GT(ToDouble(0xFFFFFFFFFFFFFFFe), -1.0);
+  EXPECT_LT(ToDouble(0xFFFFFFFFFFFFFFFe), -0.999999999);
+
+  EXPECT_EQ(ToDouble(0xFFFFFFFFFFFFFFFe), ToDouble(0xFFFFFFFFFFFFFC00));
+  EXPECT_EQ(ToDouble(0x7FFFFFFFFFFFFFFF), ToDouble(0x7FFFFFFFFFFFFC00));
+  EXPECT_NE(ToDouble(0xFFFFFFFFFFFFFFFe), ToDouble(0xFFFFFFFFFFFFF3FF));
+  EXPECT_NE(ToDouble(0x7FFFFFFFFFFFFFFF), ToDouble(0x7FFFFFFFFFFFF3FF));
+
+  EXPECT_EQ(ToDouble(0x1000000000000001), 0.125);
+  EXPECT_EQ(ToDouble(0x2000000000000001), 0.25);
+  EXPECT_EQ(ToDouble(0x3000000000000001), 0.375);
+  EXPECT_EQ(ToDouble(0x4000000000000001), 0.5);
+  EXPECT_EQ(ToDouble(0x5000000000000001), 0.625);
+  EXPECT_EQ(ToDouble(0x6000000000000001), 0.75);
+  EXPECT_EQ(ToDouble(0x7000000000000001), 0.875);
+  EXPECT_EQ(ToDouble(0x7800000000000001), 0.9375);
+  EXPECT_EQ(ToDouble(0x7c00000000000001), 0.96875);
+  EXPECT_EQ(ToDouble(0x7e00000000000001), 0.984375);
+  EXPECT_EQ(ToDouble(0x7f00000000000001), 0.9921875);
+
+  // 0x8000000000000000 ~= 0
+  EXPECT_EQ(ToDouble(0x9000000000000001), -0.125);
+  EXPECT_EQ(ToDouble(0xa000000000000001), -0.25);
+  EXPECT_EQ(ToDouble(0xb000000000000001), -0.375);
+  EXPECT_EQ(ToDouble(0xc000000000000001), -0.5);
+  EXPECT_EQ(ToDouble(0xd000000000000001), -0.625);
+  EXPECT_EQ(ToDouble(0xe000000000000001), -0.75);
+  EXPECT_EQ(ToDouble(0xf000000000000001), -0.875);
+
+  // Large powers of 2.
+  int64_t two_to_53 = int64_t{1} << 53;
+  EXPECT_EQ(static_cast<int64_t>(ToDouble(0x7FFFFFFFFFFFFFFF) * two_to_53),
+            two_to_53 - 1);
+  EXPECT_EQ(static_cast<int64_t>(ToDouble(0xFFFFFFFFFFFFFFFF) * two_to_53),
+            -(two_to_53 - 1));
+
+  EXPECT_NE(static_cast<int64_t>(ToDouble(0x7FFFFFFFFFFFFFFF) * two_to_53 * 2),
+            two_to_53 * 2 - 1);
+
+  // For values where every bit counts, the values scale as multiples of the
+  // input.
+  for (int i = 1; i < 100; ++i) {
+    EXPECT_EQ(i * e_plus, ToDouble(i)) << i;
+    EXPECT_EQ(i * e_minus, ToDouble(0x8000000000000000 | i)) << i;
+  }
+}
+
+TEST(DistributionImplTest, ExhaustiveFloat) {
+  using absl::base_internal::CountLeadingZeros64;
+  auto ToFloat = [](uint64_t a) {
+    return RandU64ToFloat<PositiveValueT, true>(a);
+  };
+
+  // Rely on RandU64ToFloat generating values from greatest to least when
+  // supplied with uint64_t values from greatest (0xfff...) to least (0x0).  Thus,
+  // this algorithm stores the previous value, and if the new value is at
+  // greater than or equal to the previous value, then there is a collision in
+  // the generation algorithm.
+  //
+  // Use the computation below to convert the random value into a result:
+  //   double res = a() * (1.0f - sample) + b() * sample;
+  float last_f = 1.0, last_g = 2.0;
+  uint64_t f_collisions = 0, g_collisions = 0;
+  uint64_t f_unique = 0, g_unique = 0;
+  uint64_t total = 0;
+  auto count = [&](const float r) {
+    total++;
+    // `f` is mapped to the range [0, 1) (default)
+    const float f = 0.0f * (1.0f - r) + 1.0f * r;
+    if (f >= last_f) {
+      f_collisions++;
+    } else {
+      f_unique++;
+      last_f = f;
+    }
+    // `g` is mapped to the range [1, 2)
+    const float g = 1.0f * (1.0f - r) + 2.0f * r;
+    if (g >= last_g) {
+      g_collisions++;
+    } else {
+      g_unique++;
+      last_g = g;
+    }
+  };
+
+  size_t limit = absl::GetFlag(FLAGS_absl_random_test_trials);
+
+  // Generate all uint64_t which have unique floating point values.
+  // Counting down from 0xFFFFFFFFFFFFFFFFu ... 0x0u
+  uint64_t x = ~uint64_t(0);
+  for (; x != 0 && limit > 0;) {
+    constexpr int kDig = (64 - FLT_MANT_DIG);
+    // Set a decrement value & the next point at which to change
+    // the decrement value. By default these are 1, 0.
+    uint64_t dec = 1;
+    uint64_t chk = 0;
+
+    // Adjust decrement and check value based on how many leading 0
+    // bits are set in the current value.
+    const int clz = CountLeadingZeros64(x);
+    if (clz < kDig) {
+      dec <<= (kDig - clz);
+      chk = (~uint64_t(0)) >> (clz + 1);
+    }
+    for (; x > chk && limit > 0; x -= dec) {
+      count(ToFloat(x));
+      --limit;
+    }
+  }
+
+  static_assert(FLT_MANT_DIG == 24,
+                "The float type is expected to have a 24 bit mantissa.");
+
+  if (limit != 0) {
+    // There are between 2^28 and 2^29 unique values in the range [0, 1).  For
+    // the low values of x, there are 2^24 -1 unique values.  Once x > 2^24,
+    // there are 40 * 2^24 unique values. Thus:
+    // (2 + 4 + 8 ... + 2^23) + 40 * 2^23
+    EXPECT_LT(1 << 28, f_unique);
+    EXPECT_EQ((1 << 24) + 40 * (1 << 23) - 1, f_unique);
+    EXPECT_EQ(total, f_unique);
+    EXPECT_EQ(0, f_collisions);
+
+    // Expect at least 2^23 unique values for the range [1, 2)
+    EXPECT_LE(1 << 23, g_unique);
+    EXPECT_EQ(total - g_unique, g_collisions);
+  }
+}
+
+TEST(DistributionImplTest, MultiplyU64ToU128Test) {
+  using absl::random_internal::MultiplyU64ToU128;
+  constexpr uint64_t k1 = 1;
+  constexpr uint64_t kMax = ~static_cast<uint64_t>(0);
+
+  EXPECT_EQ(absl::uint128(0), MultiplyU64ToU128(0, 0));
+
+  // Max uint64
+  EXPECT_EQ(MultiplyU64ToU128(kMax, kMax),
+            absl::MakeUint128(0xfffffffffffffffe, 0x0000000000000001));
+  EXPECT_EQ(absl::MakeUint128(0, kMax), MultiplyU64ToU128(kMax, 1));
+  EXPECT_EQ(absl::MakeUint128(0, kMax), MultiplyU64ToU128(1, kMax));
+  for (int i = 0; i < 64; ++i) {
+    EXPECT_EQ(absl::MakeUint128(0, kMax) << i,
+              MultiplyU64ToU128(kMax, k1 << i));
+    EXPECT_EQ(absl::MakeUint128(0, kMax) << i,
+              MultiplyU64ToU128(k1 << i, kMax));
+  }
+
+  // 1-bit x 1-bit.
+  for (int i = 0; i < 64; ++i) {
+    for (int j = 0; j < 64; ++j) {
+      EXPECT_EQ(absl::MakeUint128(0, 1) << (i + j),
+                MultiplyU64ToU128(k1 << i, k1 << j));
+      EXPECT_EQ(absl::MakeUint128(0, 1) << (i + j),
+                MultiplyU64ToU128(k1 << i, k1 << j));
+    }
+  }
+
+  // Verified multiplies
+  EXPECT_EQ(MultiplyU64ToU128(0xffffeeeeddddcccc, 0xbbbbaaaa99998888),
+            absl::MakeUint128(0xbbbb9e2692c5dddc, 0xc28f7531048d2c60));
+  EXPECT_EQ(MultiplyU64ToU128(0x0123456789abcdef, 0xfedcba9876543210),
+            absl::MakeUint128(0x0121fa00ad77d742, 0x2236d88fe5618cf0));
+  EXPECT_EQ(MultiplyU64ToU128(0x0123456789abcdef, 0xfdb97531eca86420),
+            absl::MakeUint128(0x0120ae99d26725fc, 0xce197f0ecac319e0));
+  EXPECT_EQ(MultiplyU64ToU128(0x97a87f4f261ba3f2, 0xfedcba9876543210),
+            absl::MakeUint128(0x96fbf1a8ae78d0ba, 0x5a6dd4b71f278320));
+  EXPECT_EQ(MultiplyU64ToU128(0xfedcba9876543210, 0xfdb97531eca86420),
+            absl::MakeUint128(0xfc98c6981a413e22, 0x342d0bbf48948200));
+}
+
+}  // namespace