Method TestUnpackAlternating

cpp/src/arrow/util/bpacking_test.cc:163–190

  }

  void TestUnpackAlternating(UnpackFunc<Int> unpack, const UnpackOptions& opts) {
    const auto num_bytes = GetNumBytes(opts.batch_size, opts.bit_width, opts.bit_offset);

    // Pick between two different bit patterns so that we always unpack starting with 1
    const uint8_t byte = opts.bit_offset % 2 == 0 ? 0b10101010 : 0b01010101;
    const std::vector<uint8_t> packed(static_cast<std::size_t>(num_bytes), byte);
    const auto unpacked = UnpackValues(packed.data(), opts, unpack);

    // Generate alternative bit sequence starting with either 0 or 1
    Int one_zero_value = 0;
    Int zero_one_value = 0;
    for (int i = 0; i < opts.bit_width; ++i) {
      zero_one_value = (zero_one_value << 1) | (i % 2);
      one_zero_value = (one_zero_value << 1) | ((i + 1) % 2);
    }

    std::vector<Int> expected;
    if (opts.bit_width % 2 == 0) {
      // For even bit_width, the same pattern repeats every time
      expected.resize(static_cast<std::size_t>(opts.batch_size), one_zero_value);
    } else {
      // For odd bit_width, we alternate a pattern leading with 0 and 1
      for (int i = 0; i < opts.batch_size; ++i) {
        expected.push_back(i % 2 == 0 ? zero_one_value : one_zero_value);
      }
    }
    EXPECT_EQ(unpacked, expected);
  }

  void TestAll(UnpackFunc<Int> unpack) {
    // There are actually many differences across the different sizes.