ceph/src/boost/libs/integer/test/mod_inverse_test.cpp

   1 /*
   2  *  (C) Copyright Nick Thompson 2018.
   3  *  Use, modification and distribution are subject to the
   4  *  Boost Software License, Version 1.0. (See accompanying file
   5  *  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   6  */
   7
   8 #include "multiprecision_config.hpp"
   9
  10 #ifndef DISABLE_MP_TESTS
  11 #include <boost/integer/mod_inverse.hpp>
  12 #include <boost/cstdint.hpp>
  13 #include <boost/optional/optional.hpp>
  14 #include <boost/core/lightweight_test.hpp>
  15 #include <boost/multiprecision/cpp_int.hpp>
  16 #include <boost/integer/common_factor.hpp>
  17
  18 using boost::multiprecision::int128_t;
  19 using boost::multiprecision::int256_t;
  20 using boost::integer::mod_inverse;
  21 using boost::integer::gcd;
  22
  23 template<class Z>
  24 void test_mod_inverse()
  25 {
  26     //Z max_arg = std::numeric_limits<Z>::max();
  27     Z max_arg = 500;
  28     for (Z modulus = 2; modulus < max_arg; ++modulus)
  29     {
  30         if (modulus % 1000 == 0)
  31         {
  32             std::cout << "Testing all inverses modulo " << modulus << std::endl;
  33         }
  34         for (Z a = 1; a < modulus; ++a)
  35         {
  36             Z gcdam = gcd(a, modulus);
  37             Z inv_a = mod_inverse(a, modulus);
  38             // Should fail if gcd(a, mod) != 1:
  39             if (gcdam > 1)
  40             {
  41                 BOOST_TEST(inv_a == 0);
  42             }
  43             else
  44             {
  45                 BOOST_TEST(inv_a > 0);
  46                 // Cast to a bigger type so the multiplication won't overflow.
  47                 int256_t a_inv = inv_a;
  48                 int256_t big_a = a;
  49                 int256_t m = modulus;
  50                 int256_t outta_be_one = (a_inv*big_a) % m;
  51                 BOOST_TEST_EQ(outta_be_one, 1);
  52             }
  53         }
  54     }
  55 }
  56
  57 int main()
  58 {
  59     test_mod_inverse<boost::int16_t>();
  60     test_mod_inverse<boost::int32_t>();
  61     test_mod_inverse<boost::int64_t>();
  62     test_mod_inverse<int128_t>();
  63
  64     return boost::report_errors();
  65 }
  66 #else
  67 int main()
  68 {
  69   return 0;
  70 }
  71 #endif