1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60

//! The utilies module provides general capabilities, that may span the
//! input modeling, models, output analysis, and simulator modules.  The
//! utilities are centered around debugging/traceability and common
//! arithmetic.

pub mod errors;

use errors::SimulationError;

/// The function evaluates a polynomial at a single value, with coefficients
/// defined as a slice, from the highest polynomial order to the zero order.
/// Horner's method is used for this polynomial evaluation
pub fn evaluate_polynomial(coefficients: &[f64], x: f64) -> Result<f64, SimulationError> {
    let highest_order_polynomial_coeff = coefficients
        .first()
        .ok_or(SimulationError::EmptyPolynomial)?;
    Ok(coefficients[0..coefficients.len() - 1]
        .iter()
        .fold(*highest_order_polynomial_coeff, |acc, coefficient| {
            coefficient + x * acc
        }))
}

/// When the `console_error_panic_hook` feature is enabled, we can call the
/// `set_panic_hook` function at least once during initialization, and then
/// we will get better error messages if our code ever panics.
///
/// For more details see
/// <https://github.com/rustwasm/console_error_panic_hook#readme>
pub fn set_panic_hook() {
    #[cfg(feature = "console_error_panic_hook")]
    console_error_panic_hook::set_once();
}

/// Integer square root calculation, using the Babylonian square-root
/// algorithm.
pub fn usize_sqrt(n: usize) -> usize {
    let mut x = n;
    let mut y = 1;
    while x > y {
        x = (x + y) / 2;
        y = n / x;
    }
    x
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn verify_usize_sqrt() {
        assert![1 == usize_sqrt(1)];
        assert![1 == usize_sqrt(3)];
        assert![2 == usize_sqrt(4)];
        assert![2 == usize_sqrt(8)];
        assert![3 == usize_sqrt(9)];
        assert![3 == usize_sqrt(15)];
    }
}