absl/random/internal/wide_multiply_test.cc

// 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/wide_multiply.h"

#include "gtest/gtest.h"
#include "absl/base/internal/bits.h"
#include "absl/numeric/int128.h"

using absl::random_internal::MultiplyU64ToU128;

namespace {

TEST(WideMultiplyTest, MultiplyU64ToU128Test) {
  constexpr uint64_t k1 = 1;
  constexpr uint64_t kMax = ~static_cast<uint64_t>(0);

  EXPECT_EQ(absl::uint128(0), MultiplyU64ToU128(0, 0));

  // Max uint64_t
  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