78 lines
2.3 KiB
C++
78 lines
2.3 KiB
C++
/*
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Copyright 2013--2018 James E. McClure, Virginia Polytechnic & State University
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This file is part of the Open Porous Media project (OPM).
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OPM 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 3 of the License, or
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(at your option) any later version.
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OPM 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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You should have received a copy of the GNU General Public License
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along with OPM. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "common/Utilities.h"
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#include <math.h>
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#include <algorithm>
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// Factor a number into it's prime factors
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std::vector<int> Utilities::factor(size_t number)
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{
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if ( number<=3 )
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return std::vector<int>(1,(int)number);
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size_t i, n, n_max;
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bool factor_found;
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// Compute the maximum number of factors
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int N_primes_max = 1;
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n = number;
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while (n >>= 1) ++N_primes_max;
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// Initialize n, factors
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n = number;
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std::vector<int> factors;
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factors.reserve(N_primes_max);
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while ( 1 ) {
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// Check if n is a trivial prime number
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if ( n==2 || n==3 || n==5 ) {
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factors.push_back( (int) n );
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break;
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}
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// Check if n is divisible by 2
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if ( n%2 == 0 ) {
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factors.push_back( 2 );
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n/=2;
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continue;
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}
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// Check each odd number until a factor is reached
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n_max = (size_t) floor(sqrt((double) n));
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factor_found = false;
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for (i=3; i<=n_max; i+=2) {
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if ( n%i == 0 ) {
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factors.push_back( i );
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n/=i;
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factor_found = true;
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break;
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}
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}
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if ( factor_found )
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continue;
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// No factors were found, the number must be prime
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factors.push_back( (int) n );
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break;
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}
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// Sort the factors
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std::sort( factors.begin(), factors.end() );
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return factors;
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}
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// Dummy function to prevent compiler from optimizing away variable
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void Utilities::nullUse( void* data )
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{
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NULL_USE(data);
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}
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