rusty-numbers/src/rational.rs

//! # Rational Numbers (fractions)
//!
//! Traits to implement:
//! * Add
//! * AddAssign
//! * Div
//! * DivAssign
//! * Mul
//! * MulAssign
//! * Neg
//! * Sub
//! * SubAssign

use crate::num::*;
use std::ops::{Add, Div, Mul, Neg, Sub};

#[derive(Debug, Copy, Clone, Eq, PartialEq)]
pub struct Frac<T: Unsigned = usize> {
    numer: T,
    denom: T,
    sign: Sign,
}

#[macro_export]
macro_rules! frac {
    ($n:literal / $d:literal) => {
        frac($n, $d)
    };
    ($n:literal / $d:literal) => {
        frac($n, $d)
    };
}

/// Create a new rational number
pub fn frac<S: Signed + Signed<Un = U>, U: Unsigned>(n: S, d: S) -> Frac<U> {
    // Converting from signed to unsigned should always be safe
    // when using the absolute value, especially since I'm converting
    // between the same bit size
    let mut sign = Sign::Positive;
    let numer = n.to_unsigned();
    let denom = d.to_unsigned();

    if n.is_neg() {
        sign = !sign;
    }

    if d.is_neg() {
        sign = !sign;
    }

    Frac { numer, denom, sign }.reduce()
}

impl<T: Unsigned> Frac<T> {
    /// Create a new rational number
    pub fn new(n: T, d: T, s: Sign) -> Frac<T> {
        if d.is_zero() {
            panic!("Fraction can not have a zero denominator");
        }

        Frac {
            numer: n,
            denom: d,
            sign: s,
        }
        .reduce()
    }

    /// Determine the output sign given the two input signs
    fn get_sign(a: Self, b: Self) -> Sign {
        if a.sign != b.sign {
            Sign::Negative
        } else {
            Sign::Positive
        }
    }

    /// Convert the fraction to its simplest form
    fn reduce(mut self) -> Self {
        let gcd = T::gcd(self.numer, self.denom);
        self.numer /= gcd;
        self.denom /= gcd;

        self
    }
}

impl<T: Unsigned + Mul<Output = T>> Mul for Frac<T> {
    type Output = Self;

    fn mul(self, rhs: Self) -> Self {
        let numer = self.numer * rhs.numer;
        let denom = self.denom * rhs.denom;
        let sign = Self::get_sign(self, rhs);

        Self::new(numer, denom, sign)
    }
}

impl<T: Unsigned + Mul<Output = T>> Div for Frac<T> {
    type Output = Self;

    fn div(self, rhs: Self) -> Self {
        let numer = self.numer * rhs.denom;
        let denom = self.denom * rhs.numer;
        let sign = Self::get_sign(self, rhs);

        Self::new(numer, denom, sign)
    }
}

impl<T: Unsigned + Add<Output = T> + Sub<Output = T> + Mul<Output = T>> Add for Frac<T> {
    type Output = Self;

    fn add(self, rhs: Self) -> Self::Output {
        let a = self;
        let b = rhs;

        // If the sign of one input differs,
        // subtraction is equivalent
        if self.sign != rhs.sign {
            if a.numer > b.numer {
                return a - b;
            } else if a.numer < b.numer {
                return b - a;
            }
        }

        // Find a common denominator if needed
        if a.denom != b.denom {
            // Let's just use the simplest method, rather than
            // worrying about reducing to the least common denominator
            let numer = (a.numer * b.denom) + (b.numer * a.denom);
            let denom = a.denom * b.denom;
            let sign = Self::get_sign(a, b);

            return Self::new(numer, denom, sign);
        }

        let numer = a.numer + b.numer;
        let denom = self.denom;
        let sign = Self::get_sign(a, b);

        Self::new(numer, denom, sign)
    }
}

impl<T: Unsigned + Sub<Output = T>> Sub for Frac<T> {
    type Output = Self;

    fn sub(self, rhs: Self) -> Self::Output {
        let a = self;
        let b = rhs;

        unimplemented!()
    }
}

impl<T: Unsigned> Neg for Frac<T> {
    type Output = Self;

    fn neg(self) -> Self::Output {
        let mut out = self.clone();
        out.sign = !self.sign;

        out
    }
}

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

    #[test]
    fn mul_test() {
        let frac1 = Frac::new(1u8, 3u8, Sign::Positive);
        let frac2 = Frac::new(2u8, 3u8, Sign::Positive);

        let expected = Frac::new(2u8, 9u8, Sign::Positive);

        assert_eq!(frac1 * frac2, expected);
    }

    #[test]
    fn add_test() {
        assert_eq!(frac!(5 / 6), frac!(1 / 3) + frac!(1 / 2));
    }

    #[test]
    fn macro_test() {
        let frac1 = frac!(1 / 3);
        let frac2 = Frac::new(1u32, 3, Sign::Positive);
        assert_eq!(frac1, frac2);

        let frac1 = -frac!(1 / 2);
        let frac2 = Frac::new(1u32, 2, Sign::Negative);
        assert_eq!(frac1, frac2);
    }
}