rusty-numbers/src/bigint.rs

//! \[WIP\] Arbitrarily large integers
//!
//! Traits to implement:
//! * Neg
//! * Rem
//! * RemAssign
//! * Sub
//! * SubAssign
use crate::num::*;
use core::ops::{
    Add, AddAssign, Div, DivAssign, Mul, MulAssign, Neg, Not, Rem, RemAssign, Sub, SubAssign,
};

#[derive(Clone, Debug)]
pub struct BigInt {
    inner: Vec<usize>,
    sign: Sign,
}

macro_rules! impl_from_smaller {
    ($($Type: ty),* ) => {
        $(
            impl From<$Type> for BigInt {
                fn from(n: $Type) -> Self {
                    let mut new = Self::default();
                    new.inner[0] = n as usize;

                    new
                }
            }
        )*
    }
}

#[cfg(target_pointer_width = "16")]
impl_from_smaller!(u8, u16);
#[cfg(target_pointer_width = "16")]
static BITS:usize = 16;

#[cfg(target_pointer_width = "32")]
impl_from_smaller!(u8, u16, u32);
#[cfg(target_pointer_width = "32")]
static BITS:usize = 32;

#[cfg(target_pointer_width = "64")]
impl_from_smaller!(u8, u16, u32, u64);
#[cfg(target_pointer_width = "64")]
static BITS:usize = 64;

impl Default for BigInt {
    fn default() -> Self {
        Self {
            inner: vec![0],
            sign: Sign::Positive,
        }
    }
}

impl From<usize> for BigInt {
    fn from(n: usize) -> Self {
        Self {
            inner: vec![n],
            sign: Sign::Positive,
        }
    }
}

impl From<&str> for BigInt {
    fn from(s: &str) -> Self {
        Self::from_str_radix(s, 10)
    }
}

impl From<String> for BigInt {
    fn from(s: String) -> Self {
        Self::from_str_radix(s, 10)
    }
}

impl BigInt {
    pub fn new() -> Self {
        Self::default()
    }

    pub fn shrink_to_fit(&mut self) {
        todo!();
    }

    pub fn from_str_radix<T: ToString>(s: T, radix: usize) -> BigInt {
        todo!();
    }
}

impl Add for BigInt {
    type Output = Self;

    fn add(self, rhs: Self) -> Self::Output {
        // @TODO: handle signs
        let mut out = BigInt::default();

        let u_digits = self.inner.len();
        let v_digits = rhs.inner.len();

        let digits = if v_digits > u_digits {
            v_digits
        } else {
            u_digits
        };

        let mut carry = 0usize;
        for i in 0..=digits {
            let a = *self.inner.get(i).unwrap_or(&0usize);
            let b = *rhs.inner.get(i).unwrap_or(&0usize);

            let (res, overflowed) = a.overflowing_add(b);
            if overflowed {
                if i == 0 {
                    out.inner[i] = res + carry;
                } else {
                    out.inner.push(res + carry);
                }
                carry = 1;
            } else {
                if res < core::usize::MAX {
                    out.inner.push(res + carry);
                    carry = 0;
                } else {
                    out.inner.push(0usize);
                    carry = 1;
                }

                carry = 0;
            }
        }

        out
    }
}

impl Sub for BigInt {
    type Output = Self;

    fn sub(self, rhs: Self) -> Self::Output {
        unimplemented!()
    }
}

impl Mul for BigInt {
    type Output = Self;

    fn mul(self, rhs: Self) -> Self::Output {
        unimplemented!()
    }
}

impl Div for BigInt {
    type Output = Self;

    fn div(self, rhs: Self) -> Self::Output {
        unimplemented!()
    }
}

impl Rem for BigInt {
    type Output = Self;

    fn rem(self, rhs: Self) -> Self::Output {
        unimplemented!()
    }
}

impl AddAssign for BigInt {
    fn add_assign(&mut self, rhs: Self) {
        *self = self.clone() + rhs;
    }
}

impl SubAssign for BigInt {
    fn sub_assign(&mut self, rhs: Self) {
        *self = self.clone() - rhs;
    }
}

impl MulAssign for BigInt {
    fn mul_assign(&mut self, rhs: Self) {
        *self = self.clone() * rhs;
    }
}

impl DivAssign for BigInt {
    fn div_assign(&mut self, rhs: Self) {
        *self = self.clone() / rhs;
    }
}

impl RemAssign for BigInt {
    fn rem_assign(&mut self, rhs: Self) {
        *self = self.clone() % rhs;
    }
}

impl Neg for BigInt {
    type Output = Self;

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

        output
    }
}

impl Not for BigInt {
    type Output = Self;

    fn not(self) -> Self::Output {
        let mut flipped: Vec<usize> = Vec::with_capacity(self.inner.len());

        for val in self.inner.iter() {
            let rev = !*val;
            flipped.push(rev);
        }

        BigInt {
            sign: self.sign,
            inner: flipped,
        }
    }
}

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

    #[test]
    fn sanity_checks() {
        let int = BigInt::from(45u8);
        assert_eq!(int.inner[0], 45usize)
    }

    #[test]
    fn test_add() {
        // MAX is 2^Bitsize - 1,
        // so the sum should be
        // [MAX -1, 1]
        // Compare base 10: 9 + 9 = 18
        let a = BigInt::from(core::usize::MAX);
        let b = BigInt::from(core::usize::MAX);

        let sum = a + b;

        assert_eq!(
            sum.inner[0],
            core::usize::MAX - 1,
            "least significant place should be MAX - 1"
        );
        assert_eq!(sum.inner[1], 1usize, "most significant place should be 1");

        let a = BigInt::from(core::usize::MAX);
        let b = BigInt::from(1usize);
        let sum = a + b;
        assert_eq!(sum.inner[0], 0usize);
        assert_eq!(sum.inner[1], 1usize);
    }

    #[test]
    fn test_not() {
        let a = BigInt::from(0u8);
        let b = !a;

        assert_eq!(b.inner[0], core::usize::MAX);
    }

    #[test]
    fn test_add_assign() {
        let mut a = BigInt::from(core::usize::MAX);
        let b = BigInt::from(core::usize::MAX);

        a += b;

        assert_eq!(
            a.inner[0],
            core::usize::MAX - 1,
            "least significant place should be MAX - 1"
        );
        assert_eq!(a.inner[1], 1usize, "most significant place should be 1");
    }
}