julia/C microbenchmark

newton.jl

function squareroot(x)
    it = x
    while abs(it*it - x) > 1e-13
        it = it - (it*it-x)/(2it)
    end
    return it
end

function time_sqrt(x)
    const num_iter = 100000
    q = zero(x)
    t = time()
    for i in 1:num_iter
        q += squareroot(x)
    end
    t = time() - t
    @show t/num_iter
    return q
end

time_sqrt(10000.0)

newton_raw.c

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

/*
gcc -O2 --std=c99 -march=native -o newton_raw newton_raw.c
clang -O2 --std=c99 -o newton_raw newton_raw.c
*/

// copied from julia
double clock_now()
{
    struct timeval now;
    gettimeofday(&now, NULL);
    return (double)now.tv_sec + (double)now.tv_usec/1.0e6;
}

double squareroot(double x)
{
    double it = x;
    while (fabs(it*it - x) > 1e-13) {
        it = it - (it*it-x)/(2*it);
    }
    return it;
}
int main()
{
    const int num_iter = 100000;
    double t = clock_now();
    volatile double sum_real = 0;
    for (int i = 0; i < num_iter; i++) {
        sum_real += squareroot(10000.0);
    }
    double t_double = clock_now() - t;
    printf("%e seconds\n", t_double/num_iter);
}