98 lines
3.2 KiB
C++
98 lines
3.2 KiB
C++
// Copyright 2017 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include "absl/random/internal/fastmath.h"
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#include "gtest/gtest.h"
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#if defined(__native_client__) || defined(__EMSCRIPTEN__)
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// NACL has a less accurate implementation of std::log2 than most of
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// the other platforms. For some values which should have integral results,
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// sometimes NACL returns slightly larger values.
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//
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// The MUSL libc used by emscripten also has a similar bug.
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#define ABSL_RANDOM_INACCURATE_LOG2
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#endif
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namespace {
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TEST(FastMathTest, IntLog2FloorTest) {
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using absl::random_internal::IntLog2Floor;
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constexpr uint64_t kZero = 0;
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EXPECT_EQ(0, IntLog2Floor(0)); // boundary. return 0.
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EXPECT_EQ(0, IntLog2Floor(1));
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EXPECT_EQ(1, IntLog2Floor(2));
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EXPECT_EQ(63, IntLog2Floor(~kZero));
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// A boundary case: Converting 0xffffffffffffffff requires > 53
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// bits of precision, so the conversion to double rounds up,
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// and the result of std::log2(x) > IntLog2Floor(x).
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EXPECT_LT(IntLog2Floor(~kZero), static_cast<int>(std::log2(~kZero)));
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for (int i = 0; i < 64; i++) {
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const uint64_t i_pow_2 = static_cast<uint64_t>(1) << i;
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EXPECT_EQ(i, IntLog2Floor(i_pow_2));
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EXPECT_EQ(i, static_cast<int>(std::log2(i_pow_2)));
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uint64_t y = i_pow_2;
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for (int j = i - 1; j > 0; --j) {
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y = y | (i_pow_2 >> j);
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EXPECT_EQ(i, IntLog2Floor(y));
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}
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}
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}
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TEST(FastMathTest, IntLog2CeilTest) {
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using absl::random_internal::IntLog2Ceil;
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constexpr uint64_t kZero = 0;
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EXPECT_EQ(0, IntLog2Ceil(0)); // boundary. return 0.
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EXPECT_EQ(0, IntLog2Ceil(1));
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EXPECT_EQ(1, IntLog2Ceil(2));
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EXPECT_EQ(64, IntLog2Ceil(~kZero));
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// A boundary case: Converting 0xffffffffffffffff requires > 53
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// bits of precision, so the conversion to double rounds up,
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// and the result of std::log2(x) > IntLog2Floor(x).
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EXPECT_LE(IntLog2Ceil(~kZero), static_cast<int>(std::log2(~kZero)));
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for (int i = 0; i < 64; i++) {
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const uint64_t i_pow_2 = static_cast<uint64_t>(1) << i;
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EXPECT_EQ(i, IntLog2Ceil(i_pow_2));
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#ifndef ABSL_RANDOM_INACCURATE_LOG2
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EXPECT_EQ(i, static_cast<int>(std::ceil(std::log2(i_pow_2))));
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#endif
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uint64_t y = i_pow_2;
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for (int j = i - 1; j > 0; --j) {
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y = y | (i_pow_2 >> j);
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EXPECT_EQ(i + 1, IntLog2Ceil(y));
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}
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}
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}
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TEST(FastMathTest, StirlingLogFactorial) {
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using absl::random_internal::StirlingLogFactorial;
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EXPECT_NEAR(StirlingLogFactorial(1.0), 0, 1e-3);
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EXPECT_NEAR(StirlingLogFactorial(1.50), 0.284683, 1e-3);
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EXPECT_NEAR(StirlingLogFactorial(2.0), 0.69314718056, 1e-4);
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for (int i = 2; i < 50; i++) {
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double d = static_cast<double>(i);
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EXPECT_NEAR(StirlingLogFactorial(d), std::lgamma(d + 1), 3e-5);
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}
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}
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} // namespace
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