BUN-test/test.c

#include <stdint.h>

uint64_t fibonacci( void ) {
    const int n = 250000;
    uint64_t a = 0, b = 1, c;

    for (int i = 2; i <= n; i++) {
        c = a + b;
        a = b;
        b = c;
    }

    return b;
}