#include<stdio.h>
#include<stdlib.h>
#include<time.h>
#include<math.h>
#include<pthread.h>

double mi, sigma;
unsigned long tn[] = {0, 0};
unsigned long n = 20000000;
double tmi[] = {.0, .0};
double *values;

pthread_t ts[2];
pthread_attr_t atr;
pthread_mutex_t sync_us;
pthread_cond_t move_on;

void * obrada(void *id){
	int tid = (int)id;
	unsigned long li, ln = 10000000, j;
	double lmi, lsigma, lsum = 0, b;
	char ime[15];
	FILE *f;
	li = 0;
	for(j = tid * 10 + 1; j <= (tid + 1) * 10; j+=1){
		sprintf(ime, "dat%d.txt", j);
		//printf("%ld krecem na %s\n", tid, ime);
		f = fopen(ime, "r");
		fscanf(f,"%lf",&b);
		while(!feof(f)){
			values[li + ln * tid] = b;
			lsum += b;
			li += 1;
			fscanf(f, "%lf",&b);
		}
		fclose(f);
		//printf("%ld gotov sa %s\n", tid, ime);
	}
	
	
	pthread_mutex_lock(&sync_us);
    
	tn[tid] = li;
	tmi[tid] = lsum;
	
	if(tn[(tid + 1) % 2] == 0){ //sta je sa drugom niti?
		pthread_cond_wait(&move_on, &sync_us); //ili je cekam pa da radim dalje...
		
		mi = (tmi[0] + tmi[1]) / (tn[0] + tn[1]);
	
		sigma = 0;
	
		for(j = 0; j < n; j++)
			sigma += (values[j] - mi)*(values[j] - mi);
		
		sigma /= n;
		
		sigma = sqrt(sigma);
		
	}
	else{ //ili mene ceka
		pthread_cond_signal(&move_on);
    }
	pthread_mutex_unlock(&sync_us);
	
	pthread_exit(NULL);
}

int main(){
	values = (double*)malloc(sizeof(double)*n);
	
	pthread_mutex_init(&sync_us, NULL);
    pthread_cond_init (&move_on, NULL);
	pthread_attr_init(&atr);
	pthread_attr_setdetachstate(&atr, PTHREAD_CREATE_JOINABLE);
	pthread_create(&ts[0], &atr, obrada, (void *)0);
	pthread_create(&ts[1], &atr, obrada, (void *)1);
	
	pthread_join(ts[0], NULL);
	pthread_join(ts[1], NULL);
	
	pthread_attr_destroy(&atr);
    pthread_mutex_destroy(&sync_us);
    pthread_cond_destroy(&move_on);
	
	printf("%lf\n", sigma);
	
	pthread_exit(NULL);
	
	return 0;
}