src/nt/residue/jacobi/lib.hpp
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|---|---|---|---|
| 1 | #pragma once | ||
| 2 | |||
| 3 | #include "../../../util/alias/num/lib.hpp" | ||
| 4 | |||
| 5 | namespace tifa_libs { | ||
| 6 | |||
| 7 | 276 | CEXP int jacobi_sym(u64 a, u64 p) NE { | |
| 8 |
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276 | retif_((assert(p & 1); !a) [[unlikely]], 0); |
| 9 | 276 | int s = 1, _ = 0; | |
| 10 |
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651 | while (a > 1) { |
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560 | if (a == p || !a || p < 2) return 0; |
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560 | if (_ = std::countr_zero(a); ((p - 1) & 7) && ((p + 1) & 7) && (_ & 1)) s = -s; |
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560 | if ((a >>= _) == 1) break; |
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375 | if ((((p - 1) & 7) * (a - 1)) & 7) s = -s; |
| 15 | 375 | swap(a, p %= a); | |
| 16 | } | ||
| 17 | 276 | return s; | |
| 18 | } | ||
| 19 | |||
| 20 | } // namespace tifa_libs | ||
| 21 |