First shot at adding bigints
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Timothy Warren 2020-03-03 16:33:21 -05:00
parent 096373789b
commit d5d9730607

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@ -20,24 +20,96 @@ pub struct BigInt {
sign: Sign, 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 = "32")]
impl_from_smaller!(u8, u16, u32);
#[cfg(target_pointer_width = "64")]
impl_from_smaller!(u8, u16, u32, u64);
#[cfg(target_pointer_width = "16")]
static BITS:usize = 16;
#[cfg(target_pointer_width = "32")]
static BITS:usize = 32;
#[cfg(target_pointer_width = "64")]
static BITS:usize = 64;
fn add(u: BigInt, v: BigInt) -> BigInt {
let mut out = BigInt::default();
let u_digits = u.inner.len();
let v_digits = v.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 = *u.inner.get(i).unwrap_or(&0usize);
let b = *v.inner.get(i).unwrap_or(&0usize);
let (res, overflowed) = a.overflowing_add(b);
// assert!(!overflowed, "Expected to overflow: {:#?}", (res, overflowed));
if overflowed {
if i == 0 {
out.inner[i] = res;
} else {
out.inner.push(res);
}
carry = core::usize::MAX - res + 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 Default for BigInt { impl Default for BigInt {
fn default() -> Self { fn default() -> Self {
Self { Self {
inner: vec![], inner: vec![0],
sign: Sign::Positive, sign: Sign::Positive,
} }
} }
} }
impl<T: Unsigned> From<T> for BigInt { impl From<usize> for BigInt {
fn from(n: T) -> Self { fn from(n: usize) -> Self {
let mut new = Self::default(); Self {
inner: vec![n],
if n > T::max_value() { sign: Sign::Positive,
new.split(n);
} }
new
} }
} }
@ -84,6 +156,17 @@ mod tests {
#[test] #[test]
fn sanity_checks() { fn sanity_checks() {
let int = BigInt::from(45u8);
assert_eq!(int.inner[0], 45usize)
}
} /* #[test]
fn test_add() {
let a = BigInt::from(core::u64::MAX);
let b = BigInt::from(core::u64::MAX);
let sum = add(a, b);
assert!(false, "{:#?} should have inner equal to {:?}", sum, core::u64::MAX as u128 + core::u64::MAX as u128);
} */
} }