#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <math.h>
#include "f.h"

int main(void)
{
        double x,res,eps;
        clock_t time;

        printf("x and EPS ");
        if((scanf("%lf",&x)!=1) || scanf("%lf",&eps)!=1)
        {
                fprintf(stderr,"Can not read x or eps\n");
                return ERROR_READ;
        }
        if(eps<0)
        {
                fprintf(stderr,"Incorrect EPS!\n");
                return ERROR_READ;
        }
        time = clock();
        res = fun(x,eps);
        printf("RESULT: %lf\nCalculation error: %lf\nTIME: %lf\n",res,fabs(res - cos(x)),((double)(clock() - time))/CLOCKS_PER_SEC);

        return 0;
}
#include<math.h>
#include "f.h"

double fun(double x,double eps)
{
    int i,flag = 0;
    double res,k;

    if(x<0)
    {
        x *= -1;
        flag = 1;
    }
    x -= floor(x/(2*M_PI))*2*M_PI;
    if(x>M_PI)
    {
        x -= M_PI;
        flag++;
    }

    if(x>1)
    {
        x -= M_PI/2;
        if(x<0)
            x *= -1;
        else
            flag++;
        k = x;
                res = x;
                for(i = 1;k>eps;i++)
                {
                        k *= x*x/(2*i*(2*i + 1));
                        if(i%2)
                                res -= k;
                        else
                                res += k;
                }
    }else
    {
                k = 1;
                res = 1;
                for(i = 1;k>eps;i++)
                {
                        k *= x*x/((2*i-1)*2*i);
                        if(i%2)
                                res -= k;
                        else
                                res += k;
                }
    }
    if(flag%2)
        res *= -1;
    return res;
}
#ifndef F_H
#define F_H

double fun(double x0, double eps);

#define ERROR_READ 1
#endif