/rust/registry/src/index.crates.io-1949cf8c6b5b557f/num-bigint-0.4.4/src/biguint/subtraction.rs

Source
#[cfg(not(u64_digit))]
use super::u32_from_u128;
use super::BigUint;

use crate::big_digit::{self, BigDigit};
use crate::UsizePromotion;

use core::cmp::Ordering::{Equal, Greater, Less};
use core::ops::{Sub, SubAssign};
use num_traits::{CheckedSub, Zero};

#[cfg(all(use_addcarry, target_arch = "x86_64"))]
use core::arch::x86_64 as arch;

#[cfg(all(use_addcarry, target_arch = "x86"))]
use core::arch::x86 as arch;

// Subtract with borrow:
#[cfg(all(use_addcarry, u64_digit))]
#[inline]
fn sbb(borrow: u8, a: u64, b: u64, out: &mut u64) -> u8 {
    // Safety: There are absolutely no safety concerns with calling `_subborrow_u64`.
    // It's just unsafe for API consistency with other intrinsics.
    unsafe { arch::_subborrow_u64(borrow, a, b, out) }
}

#[cfg(all(use_addcarry, not(u64_digit)))]
#[inline]
fn sbb(borrow: u8, a: u32, b: u32, out: &mut u32) -> u8 {
    // Safety: There are absolutely no safety concerns with calling `_subborrow_u32`.
    // It's just unsafe for API consistency with other intrinsics.
    unsafe { arch::_subborrow_u32(borrow, a, b, out) }
}

// fallback for environments where we don't have a subborrow intrinsic
#[cfg(not(use_addcarry))]
#[inline]
fn sbb(borrow: u8, a: BigDigit, b: BigDigit, out: &mut BigDigit) -> u8 {
    use crate::big_digit::SignedDoubleBigDigit;

    let difference = SignedDoubleBigDigit::from(a)
        - SignedDoubleBigDigit::from(b)
        - SignedDoubleBigDigit::from(borrow);
    *out = difference as BigDigit;
    u8::from(difference < 0)
}

pub(super) fn sub2(a: &mut [BigDigit], b: &[BigDigit]) {
    let mut borrow = 0;

    let len = Ord::min(a.len(), b.len());
    let (a_lo, a_hi) = a.split_at_mut(len);
    let (b_lo, b_hi) = b.split_at(len);

    for (a, b) in a_lo.iter_mut().zip(b_lo) {
        borrow = sbb(borrow, *a, *b, a);
    }

    if borrow != 0 {
        for a in a_hi {
            borrow = sbb(borrow, *a, 0, a);
            if borrow == 0 {
                break;
            }
        }
    }

    // note: we're _required_ to fail on underflow
    assert!(
        borrow == 0 && b_hi.iter().all(|x| *x == 0),
        "Cannot subtract b from a because b is larger than a."
    );
}

// Only for the Sub impl. `a` and `b` must have same length.
#[inline]
fn __sub2rev(a: &[BigDigit], b: &mut [BigDigit]) -> u8 {
    debug_assert!(b.len() == a.len());

    let mut borrow = 0;

    for (ai, bi) in a.iter().zip(b) {
        borrow = sbb(borrow, *ai, *bi, bi);
    }

    borrow
}

fn sub2rev(a: &[BigDigit], b: &mut [BigDigit]) {
    debug_assert!(b.len() >= a.len());

    let len = Ord::min(a.len(), b.len());
    let (a_lo, a_hi) = a.split_at(len);
    let (b_lo, b_hi) = b.split_at_mut(len);

    let borrow = __sub2rev(a_lo, b_lo);

    assert!(a_hi.is_empty());

    // note: we're _required_ to fail on underflow
    assert!(
        borrow == 0 && b_hi.iter().all(|x| *x == 0),
        "Cannot subtract b from a because b is larger than a."
    );
}

forward_val_val_binop!(impl Sub for BigUint, sub);
forward_ref_ref_binop!(impl Sub for BigUint, sub);
forward_val_assign!(impl SubAssign for BigUint, sub_assign);

impl Sub<&BigUint> for BigUint {
    type Output = BigUint;

    fn sub(mut self, other: &BigUint) -> BigUint {
        self -= other;
        self
    }
}
impl SubAssign<&BigUint> for BigUint {
    fn sub_assign(&mut self, other: &BigUint) {
        sub2(&mut self.data[..], &other.data[..]);
        self.normalize();
    }
}

impl Sub<BigUint> for &BigUint {
    type Output = BigUint;

    fn sub(self, mut other: BigUint) -> BigUint {
        let other_len = other.data.len();
        if other_len < self.data.len() {
            let lo_borrow = __sub2rev(&self.data[..other_len], &mut other.data);
            other.data.extend_from_slice(&self.data[other_len..]);
            if lo_borrow != 0 {
                sub2(&mut other.data[other_len..], &[1])
            }
        } else {
            sub2rev(&self.data[..], &mut other.data[..]);
        }
        other.normalized()
    }
}

promote_unsigned_scalars!(impl Sub for BigUint, sub);
promote_unsigned_scalars_assign!(impl SubAssign for BigUint, sub_assign);
forward_all_scalar_binop_to_val_val!(impl Sub<u32> for BigUint, sub);
forward_all_scalar_binop_to_val_val!(impl Sub<u64> for BigUint, sub);
forward_all_scalar_binop_to_val_val!(impl Sub<u128> for BigUint, sub);

impl Sub<u32> for BigUint {
    type Output = BigUint;

    #[inline]
    fn sub(mut self, other: u32) -> BigUint {
        self -= other;
        self
    }
}

impl SubAssign<u32> for BigUint {
    fn sub_assign(&mut self, other: u32) {
        sub2(&mut self.data[..], &[other as BigDigit]);
        self.normalize();
    }
}

impl Sub<BigUint> for u32 {
    type Output = BigUint;

    #[cfg(not(u64_digit))]
    #[inline]
    fn sub(self, mut other: BigUint) -> BigUint {
        if other.data.len() == 0 {
            other.data.push(self);
        } else {
            sub2rev(&[self], &mut other.data[..]);
        }
        other.normalized()
    }

    #[cfg(u64_digit)]
    #[inline]
    fn sub(self, mut other: BigUint) -> BigUint {
        if other.data.is_empty() {
            other.data.push(self as BigDigit);
        } else {
            sub2rev(&[self as BigDigit], &mut other.data[..]);
        }
        other.normalized()
    }
}

impl Sub<u64> for BigUint {
    type Output = BigUint;

    #[inline]
    fn sub(mut self, other: u64) -> BigUint {
        self -= other;
        self
    }
}

impl SubAssign<u64> for BigUint {
    #[cfg(not(u64_digit))]
    #[inline]
    fn sub_assign(&mut self, other: u64) {
        let (hi, lo) = big_digit::from_doublebigdigit(other);
        sub2(&mut self.data[..], &[lo, hi]);
        self.normalize();
    }

    #[cfg(u64_digit)]
    #[inline]
    fn sub_assign(&mut self, other: u64) {
        sub2(&mut self.data[..], &[other as BigDigit]);
        self.normalize();
    }
}

impl Sub<BigUint> for u64 {
    type Output = BigUint;

    #[cfg(not(u64_digit))]
    #[inline]
    fn sub(self, mut other: BigUint) -> BigUint {
        while other.data.len() < 2 {
            other.data.push(0);
        }

        let (hi, lo) = big_digit::from_doublebigdigit(self);
        sub2rev(&[lo, hi], &mut other.data[..]);
        other.normalized()
    }

    #[cfg(u64_digit)]
    #[inline]
    fn sub(self, mut other: BigUint) -> BigUint {
        if other.data.is_empty() {
            other.data.push(self);
        } else {
            sub2rev(&[self], &mut other.data[..]);
        }
        other.normalized()
    }
}

impl Sub<u128> for BigUint {
    type Output = BigUint;

    #[inline]
    fn sub(mut self, other: u128) -> BigUint {
        self -= other;
        self
    }
}

impl SubAssign<u128> for BigUint {
    #[cfg(not(u64_digit))]
    #[inline]
    fn sub_assign(&mut self, other: u128) {
        let (a, b, c, d) = u32_from_u128(other);
        sub2(&mut self.data[..], &[d, c, b, a]);
        self.normalize();
    }

    #[cfg(u64_digit)]
    #[inline]
    fn sub_assign(&mut self, other: u128) {
        let (hi, lo) = big_digit::from_doublebigdigit(other);
        sub2(&mut self.data[..], &[lo, hi]);
        self.normalize();
    }
}

impl Sub<BigUint> for u128 {
    type Output = BigUint;

    #[cfg(not(u64_digit))]
    #[inline]
    fn sub(self, mut other: BigUint) -> BigUint {
        while other.data.len() < 4 {
            other.data.push(0);
        }

        let (a, b, c, d) = u32_from_u128(self);
        sub2rev(&[d, c, b, a], &mut other.data[..]);
        other.normalized()
    }

    #[cfg(u64_digit)]
    #[inline]
    fn sub(self, mut other: BigUint) -> BigUint {
        while other.data.len() < 2 {
            other.data.push(0);
        }

        let (hi, lo) = big_digit::from_doublebigdigit(self);
        sub2rev(&[lo, hi], &mut other.data[..]);
        other.normalized()
    }
}

impl CheckedSub for BigUint {
    #[inline]
    fn checked_sub(&self, v: &BigUint) -> Option<BigUint> {
        match self.cmp(v) {
            Less => None,
            Equal => Some(Zero::zero()),
            Greater => Some(self.sub(v)),
        }
    }
}

Coverage Report

Created: 2026-01-16 07:00

Line	Count	Source
1		#[cfg(not(u64_digit))]
2		use super::u32_from_u128;
3		use super::BigUint;
4
5		use crate::big_digit::{self, BigDigit};
6		use crate::UsizePromotion;
7
8		use core::cmp::Ordering::{Equal, Greater, Less};
9		use core::ops::{Sub, SubAssign};
10		use num_traits::{CheckedSub, Zero};
11
12		#[cfg(all(use_addcarry, target_arch = "x86_64"))]
13		use core::arch::x86_64 as arch;
14
15		#[cfg(all(use_addcarry, target_arch = "x86"))]
16		use core::arch::x86 as arch;
17
18		// Subtract with borrow:
19		#[cfg(all(use_addcarry, u64_digit))]
20		#[inline]
21	0	fn sbb(borrow: u8, a: u64, b: u64, out: &mut u64) -> u8 {
22		// Safety: There are absolutely no safety concerns with calling `_subborrow_u64`.
23		// It's just unsafe for API consistency with other intrinsics.
24	0	unsafe { arch::_subborrow_u64(borrow, a, b, out) }
25	0	}
26
27		#[cfg(all(use_addcarry, not(u64_digit)))]
28		#[inline]
29		fn sbb(borrow: u8, a: u32, b: u32, out: &mut u32) -> u8 {
30		// Safety: There are absolutely no safety concerns with calling `_subborrow_u32`.
31		// It's just unsafe for API consistency with other intrinsics.
32		unsafe { arch::_subborrow_u32(borrow, a, b, out) }
33		}
34
35		// fallback for environments where we don't have a subborrow intrinsic
36		#[cfg(not(use_addcarry))]
37		#[inline]
38		fn sbb(borrow: u8, a: BigDigit, b: BigDigit, out: &mut BigDigit) -> u8 {
39		use crate::big_digit::SignedDoubleBigDigit;
40
41		let difference = SignedDoubleBigDigit::from(a)
42		- SignedDoubleBigDigit::from(b)
43		- SignedDoubleBigDigit::from(borrow);
44		*out = difference as BigDigit;
45		u8::from(difference < 0)
46		}
47
48	0	pub(super) fn sub2(a: &mut [BigDigit], b: &[BigDigit]) {
49	0	let mut borrow = 0;
50
51	0	let len = Ord::min(a.len(), b.len());
52	0	let (a_lo, a_hi) = a.split_at_mut(len);
53	0	let (b_lo, b_hi) = b.split_at(len);
54
55	0	for (a, b) in a_lo.iter_mut().zip(b_lo) {
56	0	borrow = sbb(borrow, a, b, a);
57	0	}
58
59	0	if borrow != 0 {
60	0	for a in a_hi {
61	0	borrow = sbb(borrow, *a, 0, a);
62	0	if borrow == 0 {
63	0	break;
64	0	}
65		}
66	0	}
67
68		// note: we're _required_ to fail on underflow
69	0	assert!(
70	0	borrow == 0 && b_hi.iter().all(\|x\| *x == 0),
71		"Cannot subtract b from a because b is larger than a."
72		);
73	0	}
74
75		// Only for the Sub impl. `a` and `b` must have same length.
76		#[inline]
77	0	fn __sub2rev(a: &[BigDigit], b: &mut [BigDigit]) -> u8 {
78	0	debug_assert!(b.len() == a.len());
79
80	0	let mut borrow = 0;
81
82	0	for (ai, bi) in a.iter().zip(b) {
83	0	borrow = sbb(borrow, ai, bi, bi);
84	0	}
85
86	0	borrow
87	0	}
88
89	0	fn sub2rev(a: &[BigDigit], b: &mut [BigDigit]) {
90	0	debug_assert!(b.len() >= a.len());
91
92	0	let len = Ord::min(a.len(), b.len());
93	0	let (a_lo, a_hi) = a.split_at(len);
94	0	let (b_lo, b_hi) = b.split_at_mut(len);
95
96	0	let borrow = __sub2rev(a_lo, b_lo);
97
98	0	assert!(a_hi.is_empty());
99
100		// note: we're _required_ to fail on underflow
101	0	assert!(
102	0	borrow == 0 && b_hi.iter().all(\|x\| *x == 0),
103		"Cannot subtract b from a because b is larger than a."
104		);
105	0	}
106
107		forward_val_val_binop!(impl Sub for BigUint, sub);
108		forward_ref_ref_binop!(impl Sub for BigUint, sub);
109		forward_val_assign!(impl SubAssign for BigUint, sub_assign);
110
111		impl Sub<&BigUint> for BigUint {
112		type Output = BigUint;
113
114	0	fn sub(mut self, other: &BigUint) -> BigUint {
115	0	self -= other;
116	0	self
117	0	}
118		}
119		impl SubAssign<&BigUint> for BigUint {
120	0	fn sub_assign(&mut self, other: &BigUint) {
121	0	sub2(&mut self.data[..], &other.data[..]);
122	0	self.normalize();
123	0	}
124		}
125
126		impl Sub<BigUint> for &BigUint {
127		type Output = BigUint;
128
129	0	fn sub(self, mut other: BigUint) -> BigUint {
130	0	let other_len = other.data.len();
131	0	if other_len < self.data.len() {
132	0	let lo_borrow = __sub2rev(&self.data[..other_len], &mut other.data);
133	0	other.data.extend_from_slice(&self.data[other_len..]);
134	0	if lo_borrow != 0 {
135	0	sub2(&mut other.data[other_len..], &[1])
136	0	}
137	0	} else {
138	0	sub2rev(&self.data[..], &mut other.data[..]);
139	0	}
140	0	other.normalized()
141	0	}
142		}
143
144		promote_unsigned_scalars!(impl Sub for BigUint, sub);
145		promote_unsigned_scalars_assign!(impl SubAssign for BigUint, sub_assign);
146		forward_all_scalar_binop_to_val_val!(impl Sub<u32> for BigUint, sub);
147		forward_all_scalar_binop_to_val_val!(impl Sub<u64> for BigUint, sub);
148		forward_all_scalar_binop_to_val_val!(impl Sub<u128> for BigUint, sub);
149
150		impl Sub<u32> for BigUint {
151		type Output = BigUint;
152
153		#[inline]
154	0	fn sub(mut self, other: u32) -> BigUint {
155	0	self -= other;
156	0	self
157	0	}
158		}
159
160		impl SubAssign<u32> for BigUint {
161	0	fn sub_assign(&mut self, other: u32) {
162	0	sub2(&mut self.data[..], &[other as BigDigit]);
163	0	self.normalize();
164	0	}
165		}
166
167		impl Sub<BigUint> for u32 {
168		type Output = BigUint;
169
170		#[cfg(not(u64_digit))]
171		#[inline]
172		fn sub(self, mut other: BigUint) -> BigUint {
173		if other.data.len() == 0 {
174		other.data.push(self);
175		} else {
176		sub2rev(&[self], &mut other.data[..]);
177		}
178		other.normalized()
179		}
180
181		#[cfg(u64_digit)]
182		#[inline]
183	0	fn sub(self, mut other: BigUint) -> BigUint {
184	0	if other.data.is_empty() {
185	0	other.data.push(self as BigDigit);
186	0	} else {
187	0	sub2rev(&[self as BigDigit], &mut other.data[..]);
188	0	}
189	0	other.normalized()
190	0	}
191		}
192
193		impl Sub<u64> for BigUint {
194		type Output = BigUint;
195
196		#[inline]
197	0	fn sub(mut self, other: u64) -> BigUint {
198	0	self -= other;
199	0	self
200	0	}
201		}
202
203		impl SubAssign<u64> for BigUint {
204		#[cfg(not(u64_digit))]
205		#[inline]
206		fn sub_assign(&mut self, other: u64) {
207		let (hi, lo) = big_digit::from_doublebigdigit(other);
208		sub2(&mut self.data[..], &[lo, hi]);
209		self.normalize();
210		}
211
212		#[cfg(u64_digit)]
213		#[inline]
214	0	fn sub_assign(&mut self, other: u64) {
215	0	sub2(&mut self.data[..], &[other as BigDigit]);
216	0	self.normalize();
217	0	}
218		}
219
220		impl Sub<BigUint> for u64 {
221		type Output = BigUint;
222
223		#[cfg(not(u64_digit))]
224		#[inline]
225		fn sub(self, mut other: BigUint) -> BigUint {
226		while other.data.len() < 2 {
227		other.data.push(0);
228		}
229
230		let (hi, lo) = big_digit::from_doublebigdigit(self);
231		sub2rev(&[lo, hi], &mut other.data[..]);
232		other.normalized()
233		}
234
235		#[cfg(u64_digit)]
236		#[inline]
237	0	fn sub(self, mut other: BigUint) -> BigUint {
238	0	if other.data.is_empty() {
239	0	other.data.push(self);
240	0	} else {
241	0	sub2rev(&[self], &mut other.data[..]);
242	0	}
243	0	other.normalized()
244	0	}
245		}
246
247		impl Sub<u128> for BigUint {
248		type Output = BigUint;
249
250		#[inline]
251	0	fn sub(mut self, other: u128) -> BigUint {
252	0	self -= other;
253	0	self
254	0	}
255		}
256
257		impl SubAssign<u128> for BigUint {
258		#[cfg(not(u64_digit))]
259		#[inline]
260		fn sub_assign(&mut self, other: u128) {
261		let (a, b, c, d) = u32_from_u128(other);
262		sub2(&mut self.data[..], &[d, c, b, a]);
263		self.normalize();
264		}
265
266		#[cfg(u64_digit)]
267		#[inline]
268	0	fn sub_assign(&mut self, other: u128) {
269	0	let (hi, lo) = big_digit::from_doublebigdigit(other);
270	0	sub2(&mut self.data[..], &[lo, hi]);
271	0	self.normalize();
272	0	}
273		}
274
275		impl Sub<BigUint> for u128 {
276		type Output = BigUint;
277
278		#[cfg(not(u64_digit))]
279		#[inline]
280		fn sub(self, mut other: BigUint) -> BigUint {
281		while other.data.len() < 4 {
282		other.data.push(0);
283		}
284
285		let (a, b, c, d) = u32_from_u128(self);
286		sub2rev(&[d, c, b, a], &mut other.data[..]);
287		other.normalized()
288		}
289
290		#[cfg(u64_digit)]
291		#[inline]
292	0	fn sub(self, mut other: BigUint) -> BigUint {
293	0	while other.data.len() < 2 {
294	0	other.data.push(0);
295	0	}
296
297	0	let (hi, lo) = big_digit::from_doublebigdigit(self);
298	0	sub2rev(&[lo, hi], &mut other.data[..]);
299	0	other.normalized()
300	0	}
301		}
302
303		impl CheckedSub for BigUint {
304		#[inline]
305	0	fn checked_sub(&self, v: &BigUint) -> Option<BigUint> {
306	0	match self.cmp(v) {
307	0	Less => None,
308	0	Equal => Some(Zero::zero()),
309	0	Greater => Some(self.sub(v)),
310		}
311	0	}
312		}