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1 #ifndef BLANK_RAND_GALOISLFSR_HPP_
2 #define BLANK_RAND_GALOISLFSR_HPP_
3
4 #include <cstdint>
5 #include <limits>
6
7
8 namespace blank {
9
10 class GaloisLFSR {
11
12 public:
13         // seed should be non-zero
14         explicit GaloisLFSR(std::uint64_t seed) noexcept
15         : state(seed) {
16                 if (state == 0) {
17                         state = 1;
18                 }
19         }
20
21         // get the next bit
22         bool operator ()() noexcept {
23                 bool result = state & 1;
24                 state >>= 1;
25                 if (result) {
26                         state |= 0x8000000000000000;
27                         state ^= mask;
28                 } else {
29                         state &= 0x7FFFFFFFFFFFFFFF;
30                 }
31                 return result;
32         }
33
34         template<class T>
35         T operator ()(T &out) noexcept {
36                 constexpr int num_bits =
37                         std::numeric_limits<T>::digits +
38                         std::numeric_limits<T>::is_signed;
39                 for (int i = 0; i < num_bits; ++i) {
40                         operator ()();
41                 }
42                 return out = static_cast<T>(state);
43         }
44
45         template<class T>
46         T Next() noexcept {
47                 T next;
48                 return (*this)(next);
49         }
50
51 private:
52         std::uint64_t state;
53         // bits 64, 63, 61, and 60 set to 1 (counting from 1 lo to hi)
54         static constexpr std::uint64_t mask = 0xD800000000000000;
55
56 };
57
58 }
59
60 #endif