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/*
* Each new term in the Fibonacci sequence is generated by adding the
* previous two terms. By starting with 1 and 2, the first 10 terms will be:
*
* 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
*
* By considering the terms in the Fibonacci sequence whose values do not
* exceed four million, find the sum of the even-valued terms.
*/
#include <stdio.h>
#include <math.h>
#include "utils.h"
// /* http://www.evanmiller.org/mathematical-hacker.html */
// long int fib(unsigned long int n)
// {
// return lround((pow(0.5 + 0.5 * sqrt(5.0), n) -
// pow(0.5 - 0.5 * sqrt(5.0), n)) / sqrt(5.0));
// }
// /* http://blog.noblemail.ca/2013/01/on-calculating-fibonacci-numbers-in-c.html */
// long int fib2(unsigned long int n)
// {
// return lround((pow(0.5 + 0.5 * sqrt(5.0), n)) / sqrt(5.0));
// }
int main(int argc, char **argv)
{
int i = 0;
int last = 0;
int sum = 0;
last = fib(2);
for (i = 3; last <= 4000000; i++)
{
/* even, if the lsb is 0 */
if (!(last & 1))
{
sum += last;
}
last = fib(i);
}
printf("result: %d\n", sum);
return 0;
}
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