Simplify polynomial evaluation function

[ladezai]

Hi, just wanted to share a minor improvement in src/function/evaluate.rs. The function polynomial is shorter and addresses the edge case n == 0 directly, no branching needed.

For any further modification feel free to comment/change. Any feedback is appreciated.

Details

I used the following code on rust playground (with release compile flag), and it seems to perform the same in terms of time execution.

use std::time::Instant;

pub fn polynomial(z: f64, coeff: &[f64]) -> f64 {
    let n = coeff.len();
    if n == 0 {
        return 0.0;
    }

    let mut sum = *coeff.last().unwrap();
    for c in coeff[0..n - 1].iter().rev() {
        sum = *c + z * sum;
    }
    sum
}

pub fn polynomial2(z: f64, coeff: &[f64]) -> f64 {
    coeff.into_iter().rev().fold(0_f64, |acc, val| acc * z + val)
}

pub fn main() {
    println!("Edge case with an empty coeff: {:?}", polynomial2(321.231231_f64, &[]));

    let (z, coeffs) = (32.12, [3.0_f64, -2.0_f64, 7.0_f64, 123.0_f64, 12.1_f64]);
    let now = Instant::now();
    for _i in 0.. 100 {
        polynomial(z, &coeffs);
    }
    let elapsed = now.elapsed();
    println!("Polynomial 1: {elapsed:?}");
    
    let now = Instant::now();
    for _i in 0.. 100 {
        polynomial2(z, &coeffs);
    }
    let elapsed = now.elapsed();
    println!("Polynomial 2: {elapsed:?}");
    
    let now = Instant::now();
    for _i in 0.. 100 {
        polynomial(z, &coeffs);
    }
    let elapsed = now.elapsed();
    println!("Polynomial 1: {elapsed:?}");

    println!("Difference: {:?}", polynomial(z, &coeffs) - polynomial2(z, &coeffs));
}