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/* Ergo, version 3.5, a program for linear scaling electronic structure
* calculations.
* Copyright (C) 2016 Elias Rudberg, Emanuel H. Rubensson, Pawel Salek,
* and Anastasia Kruchinina.
*
* This program 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 3 of the License, or
* (at your option) any later version.
*
* This program 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 this program. If not, see <http://www.gnu.org/licenses/>.
*
* Primary academic reference:
* KohnâSham Density Functional Theory Electronic Structure Calculations
* with Linearly Scaling Computational Time and Memory Usage,
* Elias Rudberg, Emanuel H. Rubensson, and Pawel Salek,
* J. Chem. Theory Comput. 7, 340 (2011),
* <http://dx.doi.org/10.1021/ct100611z>
*
* For further information about Ergo, see <http://www.ergoscf.org>.
*/
#include <math.h>
#include "ergo_math.h"
#ifdef PRECISION_LONG_DOUBLE
ergo_real
ergo_sqrt(ergo_real x)
{
ergo_real y, prevy, modfactor, absdiff, test;
int latestMove;
if(x == 0)
return 0;
y = 1;
modfactor = 2;
latestMove = 0;
prevy = 0;
while(1)
{
test = y*y;
absdiff = test - x;
if(absdiff < 0) absdiff *= -1;
if(test > x)
{
if(latestMove == 1)
modfactor -= (modfactor-1)*0.5;
y /= modfactor;
latestMove = -1;
}
else
{
if(latestMove == -1)
modfactor -= (modfactor-1)*0.5;
y *= modfactor;
latestMove = 1;
}
if(y == prevy)
return y;
prevy = y;
}
}
#endif
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