rusty-numbers/src/num.rs

//! Numeric Helper Traits
//!
//! Home to the numeric trait chain of doom, aka `Unsigned`
#![allow(unused_comparisons)]
use core::convert::TryFrom;
use core::fmt::Debug;
use core::ops::{
    Add, AddAssign, BitAnd, BitAndAssign, BitOr, BitOrAssign, BitXor, BitXorAssign, Div, DivAssign,
    Mul, MulAssign, Not, Rem, RemAssign, Shl, ShlAssign, Shr, ShrAssign, Sub, SubAssign,
};

/// Represents the sign of a rational number
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
#[repr(u8)]
pub enum Sign {
    /// Greater than zero, or zero
    Positive,

    /// Less than zero
    Negative,
}

impl Default for Sign {
    fn default() -> Self {
        Sign::Positive
    }
}

impl Not for Sign {
    type Output = Sign;

    fn not(self) -> Self::Output {
        match self {
            Self::Positive => Self::Negative,
            Self::Negative => Self::Positive,
        }
    }
}

/// Native number type
pub trait Num:
    Add
    + AddAssign
    + Debug
    + Div
    + DivAssign
    + Mul
    + MulAssign
    + Rem
    + RemAssign
    + PartialOrd
    + PartialEq
    + Copy
    + Sub
    + SubAssign
{
    /// Implement absolute value function for unsigned numbers
    fn abs(self) -> Self {
        self
    }
}

/// Integer primitive
pub trait Int:
    Num
    + BitAnd
    + BitAndAssign
    + BitOr
    + BitOrAssign
    + BitXor
    + BitXorAssign
    + Eq
    + Ord
    + Not
    + Shl
    + Shr
    + ShlAssign
    + ShrAssign
{
    /// Associated type for unsigned conversion
    type Un;

    /// The maximum value of the type
    fn max_value() -> Self;

    /// Is this a zero value?
    fn is_zero(self) -> bool;

    /// Is this number less than zero?
    fn is_neg(self) -> bool;

    /// Returns a tuple of the subtraction along with a boolean indicating whether an arithmetic
    /// overflow would occur. If an overflow would have occurred then the wrapped value is returned.
    fn left_overflowing_sub(self, rhs: Self) -> (Self, bool);

    /// Convert to an unsigned number
    ///
    /// A meaningless operation when implemented on an
    /// unsigned type, but the interface consistency solves
    /// other issues
    fn to_unsigned(self) -> Self::Un;
}

/// A Trait representing unsigned integer primitives
pub trait Unsigned:
    Int + Add<Output = Self> + Sub<Output = Self> + Mul<Output = Self> + Div<Output = Self>
{
    /// Find the greatest common denominator of two numbers
    fn gcd(a: Self, b: Self) -> Self;

    /// Find the least common multiple of two numbers
    fn lcm(a: Self, b: Self) -> Self;
}

/// A Trait representing signed integer primitives
pub trait Signed: Int {}

macro_rules! impl_empty {
    ($Ident: ty, ($( $Type: ty ),*) ) => {
        $(
            impl $Ident for $Type {}
        )*
    }
}

macro_rules! impl_int {
    ($(($type: ty, $un_type: ty)),* ) => {
        $(
            impl Int for $type {

                type Un = $un_type;

                fn is_zero(self) -> bool {
                    self == 0
                }

                fn max_value() -> $type {
                    <$type>::max_value()
                }

                fn is_neg(self) -> bool {
                    self < 0
                }

                fn to_unsigned(self) -> $un_type {
                    let abs = <$type>::abs(self);
                    // Converting from signed to unsigned should always be safe
                    // when using the absolute value, especially since I'm converting
                    // between the same bit size
                    <$un_type>::try_from(abs).unwrap()
                }

                fn left_overflowing_sub(self, rhs: Self) -> (Self, bool) {
                    let (res, overflow) = <$type>::overflowing_sub(self, rhs);
                    let res = if overflow {
                        <$type>::max_value() - res + 1
                    } else {
                        res
                    };

                    (res, overflow)
                }
            }
        )*
    }
}

macro_rules! impl_unsigned {
    ($($Type: ty),* ) => {
        $(
            impl Unsigned for $Type {
                /// Implementation based on
                /// [Binary GCD algorithm](https://en.wikipedia.org/wiki/Binary_GCD_algorithm)
                fn gcd(a: $Type, b: $Type) -> $Type {
                    if a == b {
                        return a;
                    } else if a == 0 {
                        return b;
                    } else if b == 0 {
                        return a;
                    }

                    let a_even = a % 2 == 0;
                    let b_even = b % 2 == 0;

                    if a_even {
                        if b_even {
                            // Both a & b are even
                            return Self::gcd(a >> 1, b >> 1) << 1;
                        } else if !b_even {
                            // b is odd
                            return Self::gcd(a >> 1, b);
                        }
                    }

                    // a is odd, b is even
                    if (!a_even) && b_even {
                        return Self::gcd(a, b >> 1);
                    }

                    if a > b {
                        return Self::gcd((a - b) >> 1, b);
                    }

                    Self::gcd((b - a) >> 1, a)
                }

                fn lcm(a: $Type, b: $Type) -> $Type {
                    if (a == 0 && b == 0) {
                        return 0;
                    }

                    a * b / Self::gcd(a, b)
                }
            }
        )*
    };
}

impl_empty!(Num, (i8, u8, i16, u16, i32, u32, i64, u64, i128, u128, isize, usize));
impl_int!(
    (i8, u8),
    (u8, u8),
    (i16, u16),
    (u16, u16),
    (i32, u32),
    (u32, u32),
    (i64, u64),
    (u64, u64),
    (i128, u128),
    (u128, u128),
    (isize, usize),
    (usize, usize)
);
impl_unsigned!(u8, u16, u32, u64, u128, usize);
impl_empty!(Signed, (i8, i16, i32, i64, i128, isize));

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

    #[test]
    fn test_los() {
        assert_eq!(4u8.left_overflowing_sub(2).0, 2u8);
        assert_eq!(0u8.left_overflowing_sub(2).0, 2u8);
    }

    #[test]
    fn test_gcd() {
        assert_eq!(u8::gcd(2, 3), 1);
        assert_eq!(u8::gcd(2, 2), 2);
        assert_eq!(u8::gcd(2, 8), 2);
        assert_eq!(u16::gcd(36, 48), 12);
    }

    #[test]
    fn test_lcm() {
        assert_eq!(u32::lcm(2, 8), 8);
        assert_eq!(u16::lcm(2, 3), 6);
        assert_eq!(usize::lcm(15, 30), 30);
        assert_eq!(u128::lcm(1, 5), 5);
        assert_eq!(0u8, u8::lcm(0, 0));
    }
}