Why does a shared object library compiled with Rust run slower with ctypes?

Question

Taking this documentation, I improperly wrote a function that calculates the power of a number in Rust, compiled it to a shared object and used it in Python. Then I have written the same algorithm with Python. I tested both and Python seems to be much faster.

sum.rs (it was supposed to sum, I changed my mind later)

#[no_mangle]
pub extern fn powerof(a: i32, b: i32) -> i32 {
    let mut c: i32 = a;
    for x in 0..b {
        c = c*a;
    }
    return c;
}

trial.py

from ctypes import cdll
import time

_powerof = cdll.LoadLibrary("./libsum.so")

def timing(f):
    # http://stackoverflow.com/a/5478448
    def wrap(*args):
        time1 = time.time()
        ret = f(*args)
        time2 = time.time()
        print('{} function took {:0.4f} ms'.format(f.__name__, (time2-time1)*1000.0))
        return ret
    return wrap

@timing
def powerof(a, b):
    global _powerof
    result = _powerof.powerof(a, b)
    return int(result)

@timing
def powerof_python(a, b):
    c = a
    for i in range(b):
        c=c*a
    return c


if __name__ == "__main__":
    print(powerof(4,5))
    print(powerof(2,3))
    print(powerof(6,4))

    print(powerof_python(4,5))
    print(powerof_python(2,3))
    print(powerof_python(6,4))

I have written and compiled Rust in the most primitive way (which means, without cargo).This is how I compiled Rust code above:

rustc sum.rs --crate-type dylib

The results are as below:

1st Test

powerof function took 0.0780 ms
4096
powerof function took 0.0136 ms
16
powerof function took 0.0064 ms
7776
powerof_python function took 0.0110 ms
4096
powerof_python function took 0.0041 ms
16
powerof_python function took 0.0050 ms
7776

2nd Test

powerof function took 0.0820 ms
4096
powerof function took 0.0083 ms
16
powerof function took 0.0057 ms
7776
powerof_python function took 0.0110 ms
4096
powerof_python function took 0.0041 ms
16
powerof_python function took 0.0041 ms
7776

3rd Test

powerof function took 0.0772 ms
4096
powerof function took 0.0098 ms
16
powerof function took 0.0069 ms
7776
powerof_python function took 0.0129 ms
4096
powerof_python function took 0.0036 ms
16
powerof_python function took 0.0043 ms
7776

It seems that the same method runs much faster in Python. Why is that?

---

Update: Timing within Rust

I edited content of sum.rs as below (added main function):

#[no_mangle]
pub extern fn powerof(a: i32, b: i32) -> i32 {
    let mut c: i32 = a;
    for x in 0..b {
        c = c*a;
    }
    return c;
}

fn main() {
    let a = powerof(4,5);
    let b = powerof(2,3);
    let c = powerof(6,4);

    println!("{}",a);
    println!("{}",b);
    println!("{}",c);
}

Compiled it with:

rustc sum.rs

Then run it with time in Linux, as below (after chmod +x ./sum):

time -v ./sum

Test 1

real    0m2.035s
user    0m0.140s
sys     0m0.072s

Test 2

real    0m0.176s
user    0m0.128s
sys     0m0.040s

Test 3

real    0m0.184s
user    0m0.136s
sys     0m0.044s

With rustc -O option

Compiled as below and given executable permission:

rustc -O sum.rs

Test 1

real    0m0.169s
user    0m0.132s
sys     0m0.032s

Test 2

real    0m0.207s
user    0m0.148s
sys     0m0.048s

Test 3

real    0m0.170s
user    0m0.124s
sys     0m0.040s

---

Environment

• Python 3.5.2
• Rust 1.7.0