81 lines
2.0 KiB
C
81 lines
2.0 KiB
C
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#include <stdio.h>
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#include <stdlib.h>
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#include <pthread.h>
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#include <sys/time.h>
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#define MAX_THREADS 64
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#define N 1000000000LL
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long long global_sum = 0;
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long long nelems_per_thread;
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pthread_mutex_t mutex;
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void *sum_squares_thread(void *arg)
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{
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long long start = *(long long *)arg;
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long long end = start + nelems_per_thread;
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if (end > N) end = N;
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long long local_sum = 0;
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for (long long i = start; i < end; i++) {
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local_sum += i * i;
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}
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pthread_mutex_lock(&mutex);
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global_sum += local_sum;
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pthread_mutex_unlock(&mutex);
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return NULL;
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}
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double get_time()
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{
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struct timeval tv;
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gettimeofday(&tv, NULL);
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return tv.tv_sec + tv.tv_usec / 1000000.0;
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}
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int main(int argc, char *argv[])
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{
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if (argc != 2) {
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fprintf(stderr, "Usage: %s <num_threads>\n", argv[0]);
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return 1;
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}
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int nthreads = atoi(argv[1]);
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if (nthreads > MAX_THREADS) nthreads = MAX_THREADS;
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nelems_per_thread = N / nthreads;
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pthread_mutex_init(&mutex, NULL);
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pthread_t threads[MAX_THREADS];
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long long starts[MAX_THREADS];
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global_sum = 0;
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double t_start = get_time();
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for (int i = 0; i < nthreads; i++) {
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starts[i] = i * nelems_per_thread;
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pthread_create(&threads[i], NULL, sum_squares_thread, &starts[i]);
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}
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for (int i = 0; i < nthreads; i++) {
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pthread_join(threads[i], NULL);
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}
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double t_end = get_time();
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double elapsed = t_end - t_start;
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__int128 n = N;
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__int128 expected = (n - 1) * n * (2 * n - 1) / 6;
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printf("Threads: %d, Sum of squares: %lld, Expected: (see below), Time: %.6f s\n",
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nthreads, global_sum, elapsed);
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/* expected ≈ 3.33e26, too large for long long; print high/low 64-bit parts */
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unsigned long long lo = (unsigned long long)expected;
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unsigned long long hi = (unsigned long long)(expected >> 64);
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if (hi)
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printf("Expected (hex): %llx%016llx\n", hi, lo);
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else
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printf("Expected: %llu\n", lo);
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pthread_mutex_destroy(&mutex);
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return 0;
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}
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