I am currently learning Rust, and as a first exercise I wanted to implement a function that computes the nth fibonacci number:
fn main() {
for i in 0..48 {
println!("{}: {}", i, fibonacci(i));
}
}
fn fibonacci(n: u32) -> u32 {
match n {
0 => 0,
1 => 1,
_ => fibonacci(n - 1) + fibonacci(n - 2),
}
}
I run it as:
$ time cargo run --release
real 0m15.380s
user 0m15.362s
sys 0m0.014s
As an exercise, I also implemented the same algorithm in C++. I was expecting a similar performance, but the C++ code runs in 80% of the time:
#include<iostream>
unsigned int fibonacci(unsigned int n);
int main (int argc, char* argv[]) {
for(unsigned int i = 0; i < 48; ++i) {
std::cout << i << ": " << fibonacci(i) << '\n';
}
return 0;
}
unsigned int fibonacci(unsigned int n) {
if(n == 0) {
return 0;
} else if (n == 1) {
return 1;
} else {
return fibonacci(n - 1) + fibonacci(n - 2);
}
}
Compiled as:
$ g++ test.cpp -o test.exe -O2
And running:
$ time ./test.exe
real 0m12.127s
user 0m12.124s
sys 0m0.000s
Why do I see such a difference in performance? I am not interested in calculating the fibonacci faster in Rust (with a different algorithm); I am only interested on where the difference comes from. This is just an exercise in my progress as I learn Rust.