63 lines
1.6 KiB
C++
63 lines
1.6 KiB
C++
#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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