#define _XOPEN_SOURCE
#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <sys/time.h>

static const int N = 3 * 1000 * 1000;

double addem_accum(double* arr, int len, double sum) {
    if (len <= 0) return sum;
    else return addem_accum(arr + 1, len - 1, sum + *arr);
}

double addem(double* arr, int len) {
    return addem_accum(arr, len, 0.0);
}

int main(int argc, char** argv) {
    int i, j;
    double* arr;
    double result;
    struct timeval tvstart, tvend;
    srand48(35947);
    arr = malloc(N * sizeof(double));
    for (i = 0; i < N; i++) {
        arr[i] = drand48();
    }

    gettimeofday(&tvstart, NULL);
    for (i = 0; i < 100; i++) {
        result = addem(arr, N);
    }
    gettimeofday(&tvend, NULL);

    uint64_t micros = (tvend.tv_sec - tvstart.tv_sec) * 1000000 +
        (tvend.tv_usec - tvstart.tv_usec);
    printf("[%lf] %lf per iteration on average.\n", result, micros / 1.0e8);
}