Allow comparing size of Bigints, and allow comparing BigInts to number primitives
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Timothy Warren 2020-05-05 15:41:27 -04:00
parent 3f6071d196
commit e54485f12b
2 changed files with 173 additions and 35 deletions

View File

@ -13,6 +13,7 @@ use alloc::string::*;
#[cfg(feature = "std")]
use std::prelude::v1::*;
use core::cmp::{Ordering, PartialOrd, PartialEq};
use core::convert::TryInto;
use core::mem::replace;
use core::ops::{
@ -131,7 +132,7 @@ impl BigInt {
todo!();
}
fn get_digit_count(a: &Self, b: &Self) -> usize {
fn get_ceil_digit_count(a: &Self, b: &Self) -> usize {
let a_digits = a.inner.len();
let b_digits = b.inner.len();
@ -164,6 +165,38 @@ impl BigInt {
Positive
}
}
/// Normal primitive multiplication
fn prim_mul(self, rhs: Self, digits: usize) -> Self {
let mut out = BigInt::with_capacity(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);
if a == 0 || b == 0 {
out.inner.push(0);
continue;
}
let (res, overflowed) = a.overflowing_mul(b);
if overflowed {
todo!()
} else {
let (res, overflowed) = res.overflowing_add(carry);
out.inner.push(res);
carry = if overflowed { 1 } else { 0 };
}
}
out.sign = Self::get_sign(self, rhs, FracOp::Other);
out.shrink_to_fit();
out
}
}
impl Add for BigInt {
@ -178,7 +211,7 @@ impl Add for BigInt {
return self - -rhs;
}
let digits = Self::get_digit_count(&self, &rhs) + 1;
let digits = Self::get_ceil_digit_count(&self, &rhs) + 1;
let mut out = BigInt::with_capacity(digits);
let mut carry = 0usize;
@ -217,7 +250,7 @@ impl Sub for BigInt {
type Output = Self;
fn sub(self, rhs: Self) -> Self::Output {
let digits = Self::get_digit_count(&self, &rhs);
let digits = Self::get_ceil_digit_count(&self, &rhs);
let mut out = BigInt::with_capacity(digits);
// Handle cases where addition makes more sense
@ -233,16 +266,17 @@ impl Sub for BigInt {
let b = *rhs.inner.get(i).unwrap_or(&0usize);
if a >= borrow && (a - borrow) >= b {
// This is the easy way, no additional borrowing or underflow
let res = a - b - borrow;
out.inner.push(res);
borrow = 0;
} else {
// To prevent subtraction overflow, the max borrowed
// value is usize::MAX. The rest of the borrowed value
// To prevent overflow, the max borrowed value is
// usize::MAX (place-value - 1). The rest of the borrowed value
// will be added on afterwords.
// In base ten, this would be like:
// 18 - 9 = 9-9 + 9
// 15 - 8 = (9 - 8) + (5 + 1)
let rem = (a + 1) - borrow;
let res = (core::usize::MAX - b) + rem;
out.inner.push(res);
@ -263,36 +297,12 @@ impl Mul for BigInt {
type Output = Self;
fn mul(self, rhs: Self) -> Self::Output {
let input_digits = Self::get_ceil_digit_count(&self, &rhs);
// Multiplication can result in twice the number of digits
let digits = Self::get_digit_count(&self, &rhs) * 2;
let mut out = BigInt::with_capacity(digits);
let out_digits = Self::get_ceil_digit_count(&self, &rhs) * 2;
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);
if a == 0 || b == 0 {
out.inner.push(0);
continue;
}
let (res, overflowed) = a.overflowing_mul(b);
if overflowed {
todo!()
} else {
let (res, overflowed) = res.overflowing_add(carry);
out.inner.push(res);
carry = if overflowed { 1 } else { 0 };
}
}
out.sign = Self::get_sign(self, rhs, FracOp::Other);
out.shrink_to_fit();
out
self.prim_mul(rhs, out_digits)
}
}
@ -377,6 +387,48 @@ impl Not for BigInt {
}
}
impl PartialOrd for BigInt {
fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
// The signs differ
if self.sign != other.sign {
// If the signs are different, the magnitude doesn't matter
// unless the value is zero on both sides
return if self.eq(&0) && other.eq(&0) {
Some(Ordering::Equal)
} else {
self.sign.partial_cmp(&other.sign)
};
}
// Everything is the same
if self.inner == other.inner {
return Some(Ordering::Equal);
}
// The number of place values differs
if self.inner.len() != other.inner.len() {
return if self.inner.len() > other.inner.len() {
Some(Ordering::Greater)
} else {
Some(Ordering::Less)
};
}
// At this point the sign is the same, and the number of place values is equal,
// so compare the individual place values (from greatest to least) until they
// are different. At this point, the digits can not all be equal.
for i in (0usize..self.inner.len()).rev() {
if self.inner[i] < other.inner[i] {
return Some(Ordering::Less);
} else if self.inner[i] > other.inner[i] {
return Some(Ordering::Greater);
}
}
unreachable!();
}
}
macro_rules! impl_from_smaller {
($(($s: ty, $u: ty)),* ) => {
$(
@ -436,11 +488,45 @@ macro_rules! impl_from_larger {
};
}
macro_rules! impl_ord_literal {
($(($($prim: ty),+), $base: ty), *) => {
$(
$(
impl PartialEq<$prim> for BigInt {
fn eq(&self, other: &$prim) -> bool {
self == &BigInt::from(*other)
}
}
impl PartialEq<BigInt> for $prim {
fn eq(&self, other: &BigInt) -> bool {
&BigInt::from(*self) == other
}
}
impl PartialOrd<$prim> for BigInt {
fn partial_cmp(&self, other: &$prim) -> Option<Ordering> {
self.partial_cmp(&BigInt::from(*other))
}
}
impl PartialOrd<BigInt> for $prim {
fn partial_cmp(&self, other: &BigInt) -> Option<Ordering> {
(&BigInt::from(*self)).partial_cmp(other)
}
}
)+
)*
};
}
#[cfg(target_pointer_width = "32")]
impl_from_larger!((i64, u64), (i128, u128));
#[cfg(target_pointer_width = "32")]
impl_from_smaller!((i8, u8), (i16, u16), (i32, u32));
#[cfg(target_pointer_width = "32")]
impl_ord_literal!((i8,u8,i16,u16,i32,u32,i64,u64), u32);
#[cfg(target_pointer_width = "32")]
static BITS: usize = 32;
#[cfg(target_pointer_width = "64")]
@ -448,6 +534,8 @@ impl_from_larger!((i128, u128));
#[cfg(target_pointer_width = "64")]
impl_from_smaller!((i8, u8), (i16, u16), (i32, u32), (i64, u64));
#[cfg(target_pointer_width = "64")]
impl_ord_literal!((i8,u8,i16,u16,i32,u32,i64,u64), u32);
#[cfg(target_pointer_width = "64")]
static BITS: usize = 64;
#[cfg(test)]
@ -699,6 +787,31 @@ mod tests {
assert_eq!(b.inner[0], core::usize::MAX);
}
#[test]
fn test_partial_eq() {
let a = 12345u16;
let b = BigInt::from(a);
assert!(a.eq(&b));
assert!(b.eq(&a));
}
#[test]
fn test_partial_ord() {
let a = 12345u32;
let b = BigInt::from(a);
let c = 3u8;
assert_eq!(a.partial_cmp(&b), Some(Ordering::Equal));
assert_eq!(c.partial_cmp(&b), Some(Ordering::Less));
assert_eq!(b.partial_cmp(&c), Some(Ordering::Greater));
assert!(big_int!(-32) < big_int!(3));
assert!(big_int!(3) > big_int!(-32));
assert!(big_int!(152) > big_int!(132));
assert_eq!(big_int!(123), big_int!(123));
}
#[test]
fn test_from() {
// Signed numbers

View File

@ -2,7 +2,7 @@
//!
//! Home to the numeric trait chain of doom, aka `Unsigned`
#![allow(unused_comparisons)]
use core::cmp::{max, min};
use core::cmp::{max, min, Ordering};
use core::convert::TryFrom;
use core::fmt::Debug;
use core::ops::{
@ -55,6 +55,21 @@ impl Not for Sign {
}
}
impl PartialOrd for Sign {
fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
match self {
Self::Positive => match other {
Self::Positive => Some(Ordering::Equal),
Self::Negative => Some(Ordering::Greater),
},
Self::Negative => match other {
Self::Positive => Some(Ordering::Less),
Self::Negative => Some(Ordering::Equal),
}
}
}
}
/// Native number type
pub trait Num:
Add
@ -303,6 +318,16 @@ mod tests {
let ns = !s;
assert_eq!(ns, Sign::Negative);
let a = Sign::Negative;
let b = Sign::Positive;
let c = Sign::Negative;
let d = Sign::Positive;
assert_eq!(a.partial_cmp(&b), Some(Ordering::Less));
assert_eq!(b.partial_cmp(&a), Some(Ordering::Greater));
assert_eq!(a.partial_cmp(&c), Some(Ordering::Equal));
assert_eq!(b.partial_cmp(&d), Some(Ordering::Equal));
}
#[test]