#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <sys/time.h>

#define NUM_THREADS 4

long long num_steps = 1000000000;
double step;
double global_sum = 0.0;
pthread_mutex_t mutex;

void *compute_pi(void *arg) {
    int thread_id = *(int *)arg;
    double local_sum = 0.0;
    long long start = thread_id * (num_steps / NUM_THREADS);
    long long end = (thread_id + 1) * (num_steps / NUM_THREADS);
    if (thread_id == NUM_THREADS - 1) end = num_steps; // Handle remainder

    for (long long i = start; i < end; i++) {
        double x = (i + 0.5) * step;
        local_sum += 4.0 / (1.0 + x * x);
    }

    pthread_mutex_lock(&mutex);
    global_sum += local_sum;
    pthread_mutex_unlock(&mutex);

    return NULL;
}

int main(int argc, char* argv[])
{
	struct timeval TimeStampStart, TimeStampStop;
	double ExeTime;
	double pi;
	int thread_ids[NUM_THREADS];
	pthread_t threads[NUM_THREADS];

	step = 1.0 / (double)num_steps;

	// Initialize mutex
	pthread_mutex_init(&mutex, NULL);

	gettimeofday(&TimeStampStart, NULL);

	// Create threads
	for (int i = 0; i < NUM_THREADS; i++) {
		thread_ids[i] = i;
		pthread_create(&threads[i], NULL, compute_pi, &thread_ids[i]);
	}

	// Wait for threads
	for (int i = 0; i < NUM_THREADS; i++) {
		pthread_join(threads[i], NULL);
	}

	pi = global_sum * step;

	gettimeofday(&TimeStampStop, NULL);
	ExeTime = (double)(TimeStampStop.tv_sec - TimeStampStart.tv_sec) +
		(double)(TimeStampStop.tv_usec - TimeStampStart.tv_usec) * 1e-6;

	// Destroy mutex
	pthread_mutex_destroy(&mutex);

	printf("The value of PI is %15.12f\n", pi);
	printf("The time to calculate PI was %f seconds\n", ExeTime);

	return 0;
}