Clean up addition/subtraction code (#87)

Author: OTheDev

arbi/src/add.rs

@@ -1,9 +1,10 @@
 /*
-Copyright 2024 Owain Davies
+Copyright 2024-2025 Owain Davies
 SPDX-License-Identifier: Apache-2.0 OR MIT
 */
 
 use crate::Arbi;
+use crate::Digit;
 use core::cmp::Ordering;
 
 impl Ord for Arbi {
@@ -26,6 +27,56 @@ impl PartialEq for Arbi {
 
 impl Eq for Arbi {}
 
+#[inline(always)]
+pub(crate) fn s_size(digits: &[Digit]) -> usize {
+    let mut len = digits.len();
+    while len > 0 && digits[len - 1] == 0 {
+        len -= 1;
+    }
+    len
+}
+
+pub(crate) fn s_cmp_impl(
+    a: &[Digit],
+    b: &[Digit],
+    assume_normalized: bool,
+) -> Ordering {
+    let (a_size, b_size) = if assume_normalized {
+        (a.len(), b.len())
+    } else {
+        (s_size(a), s_size(b))
+    };
+    match a_size.cmp(&b_size) {
+        Ordering::Equal => {
+            for i in (0..a_size).rev() {
+                match a[i].cmp(&b[i]) {
+                    Ordering::Equal => continue,
+                    other => return other,
+                }
+            }
+            Ordering::Equal
+        }
+        other => other,
+    }
+}
+
+#[allow(dead_code)]
+pub(crate) fn s_cmp(a: &[Digit], b: &[Digit]) -> Ordering {
+    s_cmp_impl(a, b, false)
+}
+
+pub(crate) fn s_cmp_normalized(a: &[Digit], b: &[Digit]) -> Ordering {
+    debug_assert!(
+        a.is_empty() || a.last() != Some(&0),
+        "slice a not normalized"
+    );
+    debug_assert!(
+        b.is_empty() || b.last() != Some(&0),
+        "slice b not normalized"
+    );
+    s_cmp_impl(a, b, true)
+}
+
 impl Arbi {
     // Assumes x, y >= 0
     pub(crate) fn cmp_abs(x: &Self, y: &Self) -> Ordering {

arbi/src/comparisons.rs

@@ -1,9 +1,10 @@
 /*
-Copyright 2024 Owain Davies
+Copyright 2024-2025 Owain Davies
 SPDX-License-Identifier: Apache-2.0 OR MIT
 */
 
 use crate::util::to_digits::{length_digits, ToDigits};
+use crate::util::ArbiLikeView;
 use crate::{Arbi, BitCount, DDigit, Digit, SDDigit};
 use core::ops::{Div, DivAssign, Rem, RemAssign};
 
@@ -72,8 +73,8 @@ impl Arbi {
             if Arbi::cmp_abs(r, v) != core::cmp::Ordering::Less {
                 // (3)(III)(a)
                 // *r = &(*r) - v;
-                Arbi::sub_abs_inplace(r, v, false);
-                // (3)(III)(b)
+                r.isub_with_arbi_like_view(v.into()); // previously, Arbi::sub_abs_inplace(r, v, false); r = |r| - |v|
+                                                      // (3)(III)(b)
                 q.set_bit(i);
             }
         }
@@ -265,7 +266,10 @@ impl Arbi {
                     q.negate_mut();
                     *q -= 1;
                     r.negate_mut();
-                    r.dadd_inplace(d, d_sign == -1); // *r += d;
+                    r.iadd_with_arbi_like_view(ArbiLikeView {
+                        vec: d,
+                        neg: d_sign == -1,
+                    }); // *r += d;
                 }
             }
             _ => {}

arbi/src/division.rs

@@ -15,7 +15,6 @@ extern crate test;
 
 use alloc::vec::Vec;
 
-mod add;
 mod assign;
 mod assign_double;
 mod assign_integral;

arbi/src/lib.rs

@@ -0,0 +1,268 @@
+/*
+Copyright 2025 Owain Davies
+SPDX-License-Identifier: Apache-2.0 OR MIT
+*/
+
+use crate::Arbi;
+use core::ops::{Add, AddAssign, Sub, SubAssign};
+
+/// `a += &b`
+///
+/// # Examples
+/// ```
+/// use arbi::Arbi;
+/// let mut a = Arbi::from(-1234567);
+/// let b = Arbi::from(-123456);
+/// a += &b;
+/// assert_eq!(a, -1358023);
+/// ```
+impl<'a> AddAssign<&'a Arbi> for Arbi {
+    fn add_assign(&mut self, other: &'a Arbi) {
+        self.iadd(other);
+    }
+}
+
+/// `a += b`
+///
+/// # Examples
+/// ```
+/// use arbi::Arbi;
+/// let mut a = Arbi::from(-1234567);
+/// let b = Arbi::from(-123456);
+/// a += b;
+/// assert_eq!(a, -1358023);
+/// ```
+impl AddAssign<Arbi> for Arbi {
+    fn add_assign(&mut self, mut other: Self) {
+        if other.capacity() > self.capacity() {
+            core::mem::swap(self, &mut other);
+        }
+        *self += &other;
+    }
+}
+
+/// `a + b`
+///
+/// # Examples
+/// ```
+/// use arbi::Arbi;
+/// let a = Arbi::from(-1234567);
+/// let b = Arbi::from(-123456);
+/// let c = a + b;
+/// assert_eq!(c, -1358023);
+/// ```
+impl Add<Arbi> for Arbi {
+    type Output = Self;
+    fn add(mut self, other: Self) -> Self {
+        self += other;
+        self
+    }
+}
+
+/// `a + &b`
+///
+/// # Examples
+/// ```
+/// use arbi::Arbi;
+/// let a = Arbi::from(-1234567);
+/// let b = Arbi::from(-123456);
+/// let c = a + &b;
+/// assert_eq!(c, -1358023);
+/// ```
+impl<'a> Add<&'a Arbi> for Arbi {
+    type Output = Self;
+    fn add(mut self, other: &'a Arbi) -> Self {
+        self += other;
+        self
+    }
+}
+
+/// `&a + b`
+///
+/// # Examples
+/// ```
+/// use arbi::{Arbi, Digit};
+///
+/// let a = Arbi::from(-123456);
+/// let b = Arbi::from(1234567);
+/// let b_cap = b.capacity();
+/// let c = &a + b; // In this case, no memory allocation (b's memory is
+///                 // used.
+/// assert_eq!(c, 1111111);
+/// assert_eq!(c.capacity(), b_cap);
+///
+/// let a = Arbi::from(-(Digit::MAX as i128));
+/// let b = Arbi::from(-1234567);
+/// let b_cap = b.capacity();
+/// let c = &a + b; // In this case, memory allocation may or may not occur,
+///                 // depending on b's capacity.
+/// assert!(c.capacity() >= b_cap);
+/// ```
+impl Add<Arbi> for &Arbi {
+    type Output = Arbi;
+    fn add(self, mut other: Arbi) -> Arbi {
+        other += self;
+        other
+    }
+}
+
+/// `&a + &b`
+///
+/// # Examples
+/// ```
+/// use arbi::Arbi;
+/// let a = Arbi::from(-1234567);
+/// let b = Arbi::from(-123456);
+/// let c = &a + &b;
+/// assert_eq!(c, -1358023);
+/// ```
+impl<'b> Add<&'b Arbi> for &Arbi {
+    type Output = Arbi;
+    fn add(self, other: &'b Arbi) -> Arbi {
+        let mut ret;
+        if self.size() <= other.size() {
+            ret = Arbi::with_capacity_and_copy(other.size() + 1, other);
+            ret += self;
+        } else {
+            ret = Arbi::with_capacity_and_copy(self.size() + 1, self);
+            ret += other;
+        }
+        ret
+    }
+}
+
+/// `a -= &b`
+///
+/// # Examples
+/// ```
+/// use arbi::Arbi;
+/// let mut a = Arbi::from(-1234567);
+/// let b = Arbi::from(-123456);
+/// a -= &b;
+/// assert_eq!(a, -1111111);
+/// ```
+impl<'a> SubAssign<&'a Arbi> for Arbi {
+    fn sub_assign(&mut self, other: &'a Arbi) {
+        self.isub(other);
+    }
+}
+
+/// `a -= b`
+///
+/// # Examples
+/// ```
+/// use arbi::Arbi;
+/// let mut a = Arbi::from(-1234567);
+/// let b = Arbi::from(-123456);
+/// a -= b;
+/// assert_eq!(a, -1111111);
+/// ```
+impl SubAssign for Arbi {
+    fn sub_assign(&mut self, mut other: Self) {
+        if self.capacity() >= other.capacity() {
+            *self -= &other;
+        } else {
+            // -(other - self) = self - other
+            core::mem::swap(self, &mut other);
+            *self -= &other;
+            self.negate_mut();
+        }
+    }
+}
+
+/// `a - b`
+///
+/// # Examples
+/// ```
+/// use arbi::Arbi;
+/// let a = Arbi::from(-1234567);
+/// let a_cap = a.capacity();
+/// let b = Arbi::from(-123456);
+/// let c = a - b; // no memory allocation
+/// assert_eq!(c, -1111111);
+/// assert_eq!(c.capacity(), a_cap);
+/// ```
+impl Sub<Arbi> for Arbi {
+    type Output = Self;
+    fn sub(mut self, other: Self) -> Self {
+        self -= other;
+        self
+    }
+}
+
+/// `a - &b`
+///
+/// # Examples
+/// ```
+/// use arbi::Arbi;
+/// let a = Arbi::from(-1234567);
+/// let a_cap = a.capacity();
+/// let b = Arbi::from(-123456);
+/// let c = a - &b; // no memory allocation
+/// assert_eq!(c, -1111111);
+/// assert_eq!(c.capacity(), a_cap);
+/// ```
+impl<'a> Sub<&'a Arbi> for Arbi {
+    type Output = Self;
+    fn sub(mut self, other: &'a Arbi) -> Self {
+        self -= other;
+        self
+    }
+}
+
+/// `&a - b`
+///
+/// # Examples
+/// ```
+/// use arbi::{Arbi, Digit};
+///
+/// let a = Arbi::from(1234567);
+/// let b = Arbi::from(123456);
+/// let b_cap = b.capacity();
+/// let c = &a - b; // In this case, no memory allocation (b's memory is
+///                 // used.
+/// assert_eq!(c, 1111111);
+/// assert_eq!(c.capacity(), b_cap);
+///
+/// let a = Arbi::from(-(Digit::MAX as i128));
+/// let b = Arbi::from(-1234567);
+/// let b_cap = b.capacity();
+/// let c = &a - b; // In this case, no memory allocation
+/// assert_eq!(c.capacity(), b_cap);
+/// ```
+impl Sub<Arbi> for &Arbi {
+    type Output = Arbi;
+    fn sub(self, mut other: Arbi) -> Arbi {
+        // a - b = -(b - a)
+        other -= self;
+        other.negate_mut();
+        other
+    }
+}
+
+/// `&a - &b`
+///
+/// # Examples
+/// ```
+/// use arbi::Arbi;
+/// let a = Arbi::from(-1234567);
+/// let b = Arbi::from(-123456);
+/// let c = &a - &b; // memory allocation
+/// assert_eq!(c, -1111111);
+/// ```
+impl<'b> Sub<&'b Arbi> for &Arbi {
+    type Output = Arbi;
+    fn sub(self, other: &'b Arbi) -> Arbi {
+        let mut ret;
+        if self.size() <= other.size() {
+            // -(other - self) = self - other
+            ret = Arbi::with_capacity_and_copy(other.size(), other);
+            ret -= self;
+            ret.negate_mut();
+        } else {
+            ret = Arbi::with_capacity_and_copy(self.size(), self);
+            ret -= other;
+        }
+        ret
+    }
+}