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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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#include "precompiled.hpp"
#include "runtime/os.hpp"
#include "utilities/population_count.hpp"
#include "utilities/globalDefinitions.hpp"
#include "unittest.hpp"

#define BITS_IN_BYTE_ARRAY_SIZE 256

uint8_t test_popcnt_bitsInByte[BITS_IN_BYTE_ARRAY_SIZE] = {
        0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,
        1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
        1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
        2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
        1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
        2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
        2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
        3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
        1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
        2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
        2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
        3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
        2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
        3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
        3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
        4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8
};

TEST(population_count, sparse) {
  // Step through the entire input range from a random starting point,
  // verify population_count return values against the lookup table
  // approach used historically
  uint32_t step = 4711;
  for (uint32_t value = os::random() % step; value < UINT_MAX - step; value += step) {
    uint32_t lookup = test_popcnt_bitsInByte[(value >> 24) & 0xff] +
                      test_popcnt_bitsInByte[(value >> 16) & 0xff] +
                      test_popcnt_bitsInByte[(value >> 8)  & 0xff] +
                      test_popcnt_bitsInByte[ value        & 0xff];

    EXPECT_EQ(lookup, population_count(value))
        << "value = " << value;
  }

  // Test a few edge cases
  EXPECT_EQ(0u, population_count(0u))
      << "value = " << 0;
  EXPECT_EQ(1u, population_count(1u))
      << "value = " << 1;
  EXPECT_EQ(1u, population_count(2u))
      << "value = " << 2;
  EXPECT_EQ(32u, population_count(UINT_MAX))
      << "value = " << UINT_MAX;
  EXPECT_EQ(31u, population_count(UINT_MAX - 1))
      << "value = " << (UINT_MAX - 1);
}