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Diffstat (limited to 'absl/random/internal/distribution_impl_test.cc')
| -rw-r--r-- | absl/random/internal/distribution_impl_test.cc | 506 |
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 00000000..09e7a318 --- /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 |