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phosit
49 lines
1.5 KiB
C++
49 lines
1.5 KiB
C++
/* Copyright (C) 2010 Wildfire Games.
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* This file is part of 0 A.D.
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*
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* 0 A.D. is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 2 of the License, or
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* (at your option) any later version.
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*
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* 0 A.D. is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with 0 A.D. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "precompiled.h"
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#include "Sqrt.h"
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// Based on http://freaknet.org/martin/tape/gos/misc/personal/msc/sqrt/sqrt.html
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std::uint32_t isqrt64(std::uint64_t n)
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{
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std::uint64_t op = n;
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std::uint64_t res = 0;
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std::uint64_t one = static_cast<std::uint64_t>(1) << 62; // highest power of four <= than the argument
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while (one > op)
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one >>= 2;
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while (one != 0)
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{
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if (op >= res + one)
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{
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op -= (res + one);
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res += (one << 1);
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}
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res >>= 1;
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one >>= 2;
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}
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return static_cast<std::uint32_t>(res);
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}
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// TODO: This should be equivalent to static_cast<std::uint32_t>(sqrt((double)n)), and in practice
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// that seems to be true for all input, so do we actually need this integer-only
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// implementation? i.e. are there any platforms / compiler settings where
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// sqrt(double) won't give the correct answer? and is sqrt(double) faster?
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