[~]-[%] cat vecbench.hpp
#pragma once

#include <stddef.h>

struct Span {
    double *p;
    size_t n;
};

void fill_with_zeros(Span *s);

[~]-[%] cat vecbench.cpp
#include "vecbench.hpp"
#include <stddef.h>

void fill_with_zeros(Span *s)
{
    for (size_t i = 0; i < s->n; ++i) {
        s->p[i] = 0.0;
    }
}

[~]-[%] cat main.cpp
#include <vector>
#include "vecbench.hpp"

int main()
{
    std::vector<double> v(100 * 1000 * 1000, 1.0);
    Span s = {v.data(), v.size()};
    fill_with_zeros(&s);
    return v[0] == 0.0 ? 0 : 1;
}

[~]-[%] g++ -Wall -Wextra -O3 vecbench.cpp main.cpp -o main; time (repeat 10 ./main)

real	1.38s
user	0.89s
sys	0.49s
[~]-[%] g++ -Wall -Wextra -O3 -fno-strict-aliasing vecbench.cpp main.cpp -o main; time (repeat 10 ./main)

real	1.93s
user	1.44s
sys	0.48s
[~]-[%] python3
Python 3.13.12 (main, Feb  4 2026, 15:06:39) [GCC 15.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
 ● >>> 1.93 / 1.38
1.3985507246376812