// matrix_mul_serial.c
// 串行矩阵乘法，测量纯计算时间（不含矩阵生成/初始化）

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

static double get_time() {
    struct timeval tv;
    gettimeofday(&tv, NULL);
    return tv.tv_sec + tv.tv_usec * 1e-6;
}

int main(int argc, char *argv[]) {
    int N = 8000;
    if (argc >= 2) {
        N = atoi(argv[1]);
    }
    // 分配并初始化矩阵
    double *A = malloc((size_t)N * N * sizeof(double));
    double *B = malloc((size_t)N * N * sizeof(double));
    double *C = calloc((size_t)N * N, sizeof(double));
    if (!A || !B || !C) {
        fprintf(stderr, "内存分配失败\n");
        return EXIT_FAILURE;
    }
    srand(0);
    for (long long i = 0; i < (long long)N * N; i++) {
        A[i] = rand() / (double)RAND_MAX;
        B[i] = rand() / (double)RAND_MAX;
    }

    // 纯计算部分计时
    double t0 = get_time();
    for (int i = 0; i < N; i++) {
        for (int j = 0; j < N; j++) {
            double sum = 0.0;
            for (int k = 0; k < N; k++) {
                sum += A[(long long)i * N + k] * B[(long long)k * N + j];
            }
            C[(long long)i * N + j] = sum;
        }
    }
    double t1 = get_time();

    printf("Serial multiplication time: %.6f seconds\n", t1 - t0);

    free(A);
    free(B);
    free(C);
    return 0;
}