1 ///////////////////////////////////////////////////////////////
2 // Copyright 2018 John Maddock. Distributed under the Boost
3 // Software License, Version 1.0. (See accompanying file
4 // LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt).
5
6 // Contains Quickbook snippets used by boost/libs/multiprecision/doc/multiprecision.qbk,
7 // used in section Literal Types and constexpr Support, last example on constexpr randoms.
8
9 // A implementation and demonstration of the Keep It Simple Stupid random number generator algorithm https://en.wikipedia.org/wiki/KISS_(algorithm) for cpp_int integers.
10 // b2 --abbreviate-paths toolset=clang-9.0.0 address-model=64 cxxstd=2a release misc > multiprecision_clang_misc.log
11
12 #include <boost/multiprecision/cpp_int.hpp>
13
14 #include <iostream>
15
16 struct kiss_rand
17 {
18 typedef std::uint64_t result_type;
19
kiss_randkiss_rand20 constexpr kiss_rand() : x(0x8207ebe160468b32uLL), y(0x2871283e01d45bbduLL), z(0x9c80bfd5db9680c9uLL), c(0x2e2683c2abb878b8uLL) {}
kiss_randkiss_rand21 constexpr kiss_rand(std::uint64_t seed) : x(seed), y(0x2871283e01d45bbduLL), z(0x9c80bfd5db9680c9uLL), c(0x2e2683c2abb878b8uLL) {}
kiss_randkiss_rand22 constexpr kiss_rand(std::uint64_t seed_x, std::uint64_t seed_y) : x(seed_x), y(seed_y), z(0x9c80bfd5db9680c9uLL), c(0x2e2683c2abb878b8uLL) {}
kiss_randkiss_rand23 constexpr kiss_rand(std::uint64_t seed_x, std::uint64_t seed_y, std::uint64_t seed_z) : x(seed_x), y(seed_y), z(seed_z), c(0x2e2683c2abb878b8uLL) {}
24
operator ()kiss_rand25 constexpr std::uint64_t operator()()
26 {
27 return MWC() + XSH() + CNG();
28 }
29
30 private:
MWCkiss_rand31 constexpr std::uint64_t MWC()
32 {
33 std::uint64_t t = (x << 58) + c;
34 c = (x >> 6);
35 x += t;
36 c += (x < t);
37 return x;
38 }
XSHkiss_rand39 constexpr std::uint64_t XSH()
40 {
41 y ^= (y << 13);
42 y ^= (y >> 17);
43 return y ^= (y << 43);
44 }
CNGkiss_rand45 constexpr std::uint64_t CNG()
46 {
47 return z = 6906969069LL * z + 1234567;
48 }
49 std::uint64_t x, y, z, c;
50 };
51
hash_combine(std::uint64_t & h,std::uint64_t k)52 inline constexpr void hash_combine(std::uint64_t& h, std::uint64_t k)
53 {
54 constexpr const std::uint64_t m = 0xc6a4a7935bd1e995uLL;
55 constexpr const int r = 47;
56
57 k *= m;
58 k ^= k >> r;
59 k *= m;
60
61 h ^= k;
62 h *= m;
63
64 // Completely arbitrary number, to prevent 0's from hashing to 0.
65 h += 0xe6546b64;
66 }
67
68 template <std::size_t N>
string_to_hash(const char (& s)[N])69 inline constexpr std::uint64_t string_to_hash(const char (&s)[N])
70 {
71 std::uint64_t hash(0);
72 for (unsigned i = 0; i < N; ++i)
73 hash_combine(hash, s[i]);
74 return hash;
75 }
76
77 template <class UnsignedInteger>
78 struct multiprecision_generator
79 {
80 typedef UnsignedInteger result_type;
multiprecision_generatormultiprecision_generator81 constexpr multiprecision_generator(std::uint64_t seed1) : m_gen64(seed1) {}
multiprecision_generatormultiprecision_generator82 constexpr multiprecision_generator(std::uint64_t seed1, std::uint64_t seed2) : m_gen64(seed1, seed2) {}
multiprecision_generatormultiprecision_generator83 constexpr multiprecision_generator(std::uint64_t seed1, std::uint64_t seed2, std::uint64_t seed3) : m_gen64(seed1, seed2, seed3) {}
84
result_typemultiprecision_generator85 static constexpr result_type (min)()
86 {
87 return 0u;
88 }
result_typemultiprecision_generator89 static constexpr result_type (max)()
90 {
91 return ~result_type(0u);
92 }
operator ()multiprecision_generator93 constexpr result_type operator()()
94 {
95 result_type result(m_gen64());
96 unsigned digits = 64;
97 while (digits < std::numeric_limits<result_type>::digits)
98 {
99 result <<= 64;
100 result |= m_gen64();
101 digits += 64;
102 }
103 return result;
104 }
105
106 private:
107 kiss_rand m_gen64;
108 };
109
110 template <class UnsignedInteger>
nth_random_value(unsigned count=0)111 constexpr UnsignedInteger nth_random_value(unsigned count = 0)
112 {
113 std::uint64_t date_hash = string_to_hash(__DATE__);
114 std::uint64_t time_hash = string_to_hash(__TIME__);
115 multiprecision_generator<UnsignedInteger> big_gen(date_hash, time_hash);
116 for (unsigned i = 0; i < count; ++i)
117 big_gen();
118 return big_gen();
119 }
120
main()121 int main()
122 {
123 using namespace boost::multiprecision;
124
125 //[random_constexpr_cppint
126 constexpr uint1024_t rand = nth_random_value<uint1024_t>(1000);
127 std::cout << std::hex << rand << std::endl;
128 //] [/random_constexpr_cppint]
129 return 0;
130 }
131