Performance benchmark: double multiplication vs integer multiplication+shift

perf_double.c

#include <stdio.h>

#define N (100000000)

double arr[] = { 8, 0.125, 4, 0.25 };

int main() {
    double d = 1.0;
    for (int i = 0; i < N; ++i) {
        d *= arr[i % 4];
    }
    fprintf(stderr, "d = %f\n", d);
    return 0;
}

perf_int.c

#include <stdio.h>

#define N (100000000)

struct muls_t {
    long long mul;
    int shr; // shift right (division)
};

struct muls_t arr[] = { {8, 0}, {1, 3}, {4, 0}, {1, 2} };

int main() {
    long long d = 1;
    for (int i = 0; i < N; ++i) {
        struct muls_t m = arr[i % 4];
        d  = (d * m.mul) >> m.shr;
    }
    fprintf(stderr, "d = %lld\n", d);
    return 0;
}

results

# gcc perf_double.c -O3 -o pd
# gcc perf_int.c -O3 -o pi

# Mac Book Pro, late 2013
$ time ./pd 
d = 1.000000

real	0m0.177s
user	0m0.166s
sys	0m0.002s
$ time ./pd
d = 1

real	0m0.184s
user	0m0.172s
sys	0m0.002s