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/* Ergo, version 3.8.2, a program for linear scaling electronic structure
* calculations.
* Copyright (C) 2023 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:
* Ergo: An open-source program for linear-scaling electronic structure
* calculations,
* Elias Rudberg, Emanuel H. Rubensson, Pawel Salek, and Anastasia
* Kruchinina,
* SoftwareX 7, 107 (2018),
* <http://dx.doi.org/10.1016/j.softx.2018.03.005>
*
* For further information about Ergo, see <http://www.ergoscf.org>.
*/
/** @file machine_epsilon.cc
@brief Functionality for determining an approximate value of the
"machine epsilon" -- the smallest number that can be added to 1
giving a result different from 1, using the ergo_real
floating-point type.
@author: Elias Rudberg <em>responsible</em>
*/
#include "machine_epsilon.h"
/** return machine epsilon. This routine is deprecated. Use instead:
- std::numeric_limits<double>::epsilon() in C++;
- or FLT_EPSILON for single precision, DBL_EPSILON for double
precision or or LDBL_EPSILON in long double - in C.
*/
ergo_real
get_machine_epsilon()
{
ergo_real volatile x, y, z;
x = 1;
y = 0.1;
while(1)
{
z = x + y;
if(z == x)
return y;
y *= 0.98;
}
/* this point should never be reached */
return 0;
}
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