#include "lib.h"

#include <math.h>

#define ZEROIN_MAX_ITERATIONS 1000

size_t fibo(size_t n)
{
    size_t prev = 0, cur = 1, tmp = 0;
    for (size_t i = 0; i < n; i++) {
        tmp = cur;
        cur = cur + prev;
        prev = tmp;
    }
    return cur;
}

double zeroin(double (*f)(double), double err, double a, double b)
{
    double left = f(a);
    if (fabs(left) < err) return left;
    double right = f(b);
    if (fabs(right) < err) return right;
    if (left * right > 0) {
        return NAN;
    }

    double x = NAN;
    double cur = NAN;
    size_t n = 0;
    do {
        x = (a + b) / 2;
        cur = f(x);
        if (cur * left > 0) {
            left = cur;
            a = x;
        }
        else {
            right = cur;
            b = x;
        }
        n++;
    } while (fabs(cur) > err || n < ZEROIN_MAX_ITERATIONS);
    return x;
}