mirror of
https://github.com/matrix-construct/construct
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38 lines
872 B
C++
38 lines
872 B
C++
// Matrix Construct
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//
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// Copyright (C) Matrix Construct Developers, Authors & Contributors
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// Copyright (C) 2016-2021 Jason Volk <jason@zemos.net>
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//
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// Permission to use, copy, modify, and/or distribute this software for any
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// purpose with or without fee is hereby granted, provided that the above
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// copyright notice and this permission notice is present in all copies. The
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// full license for this software is available in the LICENSE file.
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#pragma once
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#define HAVE_IRCD_MATH_INV_H
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namespace ircd::math
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{
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template<class Z> constexpr Z inv(Z a, const Z m);
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}
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/// Modular Inverse
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template<class Z>
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inline constexpr Z
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ircd::math::inv(Z a,
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const Z m)
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{
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auto b{m}, x0{0}, x1{1};
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if(likely(m != 1)) while(a > 1)
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{
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auto t{b}, q{a / b};
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b = a % b;
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a = t;
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t = x0;
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x0 = x1 - q * x0;
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x1 = t;
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}
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x1 += boolmask<Z>(x1 < 0) & m;
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return x1;
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}
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