aiwork

AI-work/task64.c

@@ -0,0 +1,80 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <sys/time.h>
+
+#define MAX_THREADS 64
+#define N 1000000000LL
+
+long long global_sum = 0;
+long long nelems_per_thread;
+pthread_mutex_t mutex;
+
+void *sum_squares_thread(void *arg)
+{
+    long long start = *(long long *)arg;
+    long long end = start + nelems_per_thread;
+    if (end > N) end = N;
+    long long local_sum = 0;
+    for (long long i = start; i < end; i++) {
+        local_sum += i * i;
+    }
+    pthread_mutex_lock(&mutex);
+    global_sum += local_sum;
+    pthread_mutex_unlock(&mutex);
+    return NULL;
+}
+
+double get_time()
+{
+    struct timeval tv;
+    gettimeofday(&tv, NULL);
+    return tv.tv_sec + tv.tv_usec / 1000000.0;
+}
+
+int main(int argc, char *argv[])
+{
+    if (argc != 2) {
+        fprintf(stderr, "Usage: %s <num_threads>\n", argv[0]);
+        return 1;
+    }
+
+    int nthreads = atoi(argv[1]);
+    if (nthreads > MAX_THREADS) nthreads = MAX_THREADS;
+
+    nelems_per_thread = N / nthreads;
+    pthread_mutex_init(&mutex, NULL);
+
+    pthread_t threads[MAX_THREADS];
+    long long starts[MAX_THREADS];
+
+    global_sum = 0;
+    double t_start = get_time();
+
+    for (int i = 0; i < nthreads; i++) {
+        starts[i] = i * nelems_per_thread;
+        pthread_create(&threads[i], NULL, sum_squares_thread, &starts[i]);
+    }
+
+    for (int i = 0; i < nthreads; i++) {
+        pthread_join(threads[i], NULL);
+    }
+
+    double t_end = get_time();
+    double elapsed = t_end - t_start;
+
+    __int128 n = N;
+    __int128 expected = (n - 1) * n * (2 * n - 1) / 6;
+    printf("Threads: %d, Sum of squares: %lld, Expected: (see below), Time: %.6f s\n",
+           nthreads, global_sum, elapsed);
+    /* expected ≈ 3.33e26, too large for long long; print high/low 64-bit parts */
+    unsigned long long lo = (unsigned long long)expected;
+    unsigned long long hi = (unsigned long long)(expected >> 64);
+    if (hi)
+        printf("Expected (hex): %llx%016llx\n", hi, lo);
+    else
+        printf("Expected: %llu\n", lo);
+
+    pthread_mutex_destroy(&mutex);
+    return 0;
+}