financial 1.1.5

A collection of finance calculations mimicking some of Excel Financial Functions interface
Documentation 
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pub fn powers(base: f64, n: usize, start_from_zero: bool) -> Vec<f64> {
    let start = if start_from_zero { 0 } else { 1 };
    let p0 = if start_from_zero { 1. } else { base };

    (start..n).fold(vec![p0], |mut pows, _| {
        pows.push(pows.last().unwrap() * (base));
        pows
    })
}

pub fn trim_zeros(values: &[f64]) -> &[f64] {
    let not_zero = |x: &f64| *x != 0.;

    let begin = values.iter().position(not_zero).unwrap_or(0);

    let end = values.iter().rposition(not_zero).unwrap_or(values.len() - 1) + 1;
    &values[begin..end]
}

pub fn trim_end_zeros(values: &[f64]) -> &[f64] {
    let not_zero = |x: &f64| *x != 0.;

    let end = values.iter().rposition(not_zero).unwrap_or(values.len() - 1) + 1;

    &values[0..end]
}

use chrono::{offset::TimeZone, DateTime};

#[inline]
pub fn days_to<T: TimeZone>(d0: DateTime<T>, d1: DateTime<T>) -> f64 {
    d1.signed_duration_since(d0).num_days() as f64
}

// FIXME: needs to move
pub fn validate_cashflow_values(values: &[f64]) -> Result<(), &'static str> {
    let len = values.len();
    let zeros = values.iter().filter(|x| **x == 0.).count();
    let negatives = values.iter().filter(|x| x.is_sign_negative()).count();

    if len < 2 || zeros + negatives == len {
        return Err(
            "cashflow must contain more than one value, and include positive and negative values",
        );
    }

    Ok(())
}