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/* Copyright (C) 2010 Wildfire Games.
* This file is part of 0 A.D.
*
* 0 A.D. is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 2 of the License, or
* (at your option) any later version.
*
* 0 A.D. is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with 0 A.D. If not, see <http://www.gnu.org/licenses/>.
*/
#include "precompiled.h"
#include "Sqrt.h"
// Based on http://freaknet.org/martin/tape/gos/misc/personal/msc/sqrt/sqrt.html
u32 isqrt64(u64 n)
{
u64 op = n;
u64 res = 0;
u64 one = (u64)1 << 62; // highest power of four <= than the argument
while (one > op)
one >>= 2;
while (one != 0)
{
if (op >= res + one)
{
op -= (res + one);
res += (one << 1);
}
res >>= 1;
one >>= 2;
}
return (u32)res;
}
// TODO: This should be equivalent to (u32)sqrt((double)n), and in practice
// that seems to be true for all input, so do we actually need this integer-only
// implementation? i.e. are there any platforms / compiler settings where
// sqrt(double) won't give the correct answer? and is sqrt(double) faster?
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