primecount/test/ilog2.cpp

///
/// @file   ilog2.cpp
/// @brief  Test ilog2(x) function.
///         Note that the log2(x) function from <cmath> is not
///         accurate enough near 2^64.
///
/// Copyright (C) 2021 Kim Walisch, <kim.walisch@gmail.com>
///
/// This file is distributed under the BSD License. See the COPYING
/// file in the top level directory.
///

#include <imath.hpp>

#include <stdint.h>
#include <iostream>
#include <cmath>
#include <cstdlib>

void check(bool OK)
{
  std::cout << "   " << (OK ? "OK" : "ERROR") << "\n";
  if (!OK)
    std::exit(1);
}

int main()
{
  uint64_t n;
  uint64_t res1;
  uint64_t res2;

  for (n = 1; n < 100000; n++)
  {
    res1 = ilog2(n);
    res2 = (uint64_t) std::log2(n);
    std::cout << "ilog2(" << n << ") = " << res1;
    check(res1 == res2);
  }

  n = (1ull << 32) - 1;
  res1 = ilog2(n);
  res2 = (uint64_t) std::log2(n);
  std::cout << "ilog2(" << n << ") = " << res1;
  check(res1 == (uint64_t) res2);

  n = 1ull << 32;
  res1 = ilog2(n);
  res2 = (uint64_t) std::log2(n);
  std::cout << "ilog2(" << n << ") = " << res1;
  check(res1 == (uint64_t) res2);

  n = (1ull << 63) - 1;
  res1 = ilog2(n);
  std::cout << "ilog2(" << n << ") = " << res1;
  check(res1 == 62);

  n = 1ull << 63;
  res1 = ilog2(n);
  std::cout << "ilog2(" << n << ") = " << res1;
  check(res1 == 63);

  n = 18446744073709551615ull;
  res1 = ilog2(n);
  std::cout << "ilog2(" << n << ") = " << res1;
  check(res1 == 63);

  std::cout << std::endl;
  std::cout << "All tests passed successfully!" << std::endl;

  return 0;
}