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| 36 | template<int N, typename T = uint8_t> |
36 | template<int N, typename T = uint8_t> |
| 37 | struct permutation |
37 | struct permutation |
| 38 | { |
38 | { |
| 39 | T pmap[N]; |
39 | T pmap[N]; |
| 40 | |
40 | |
| 41 | template<class generator> |
41 | template<class random_generator> |
| 42 | void seed (generator &rng) |
42 | void seed (random_generator &rng); |
| 43 | { |
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| 44 | for (int i = 0; i < N; ++i) |
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| 45 | pmap[i] = i; |
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| 46 | |
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| 47 | // fisher-yates to randomly perturb |
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| 48 | for (int i = N; --i; ) |
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| 49 | ::swap (pmap[i], pmap[rng (i + 1)]); |
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| 50 | } |
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| 51 | |
43 | |
| 52 | T operator ()(T v) |
44 | T operator ()(T v) |
| 53 | { |
45 | { |
| 54 | return pmap[v & (N - 1)]; |
46 | return pmap[v & (N - 1)]; |
| 55 | } |
47 | } |
