/rust/registry/src/index.crates.io-6f17d22bba15001f/num-bigint-0.4.6/src/biguint/subtraction.rs

Source (jump to first uncovered line)
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;

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

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

// Subtract with borrow:
#[cfg(target_arch = "x86_64")]
cfg_64!(
    #[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(any(target_arch = "x86", target_arch = "x86_64"))]
cfg_32!(
    #[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
// (copied from the standard library's `borrowing_sub`)
#[cfg(not(any(target_arch = "x86", target_arch = "x86_64")))]
#[inline]
fn sbb(borrow: u8, lhs: BigDigit, rhs: BigDigit, out: &mut BigDigit) -> u8 {
    let (a, b) = lhs.overflowing_sub(rhs);
    let (c, d) = a.overflowing_sub(borrow as BigDigit);
    *out = c;
    u8::from(b || d)
}

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_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()
        }

        #[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_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();
        }

        #[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_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()
        }

        #[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_digit!(
        #[inline]
        fn sub_assign(&mut self, other: u128) {
            let (a, b, c, d) = super::u32_from_u128(other);
            sub2(&mut self.data[..], &[d, c, b, a]);
            self.normalize();
        }

        #[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_digit!(
        #[inline]
        fn sub(self, mut other: BigUint) -> BigUint {
            while other.data.len() < 4 {
                other.data.push(0);
            }

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

        #[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(Self::ZERO),
            Greater => Some(self.sub(v)),
        }
    }
}

Coverage Report

Created: 2025-05-08 06:26

Line	Count	Source (jump to first uncovered line)
1		use super::BigUint;
2
3		use crate::big_digit::{self, BigDigit};
4		use crate::UsizePromotion;
5
6		use core::cmp::Ordering::{Equal, Greater, Less};
7		use core::ops::{Sub, SubAssign};
8		use num_traits::CheckedSub;
9
10		#[cfg(target_arch = "x86_64")]
11		use core::arch::x86_64 as arch;
12
13		#[cfg(target_arch = "x86")]
14		use core::arch::x86 as arch;
15
16		// Subtract with borrow:
17		#[cfg(target_arch = "x86_64")]
18		cfg_64!(
19		#[inline]
20	0	fn sbb(borrow: u8, a: u64, b: u64, out: &mut u64) -> u8 {
21	0	// Safety: There are absolutely no safety concerns with calling `_subborrow_u64`.
22	0	// It's just unsafe for API consistency with other intrinsics.
23	0	unsafe { arch::_subborrow_u64(borrow, a, b, out) }
24	0	}
25		);
26
27		#[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
28		cfg_32!(
29		#[inline]
30		fn sbb(borrow: u8, a: u32, b: u32, out: &mut u32) -> u8 {
31		// Safety: There are absolutely no safety concerns with calling `_subborrow_u32`.
32		// It's just unsafe for API consistency with other intrinsics.
33		unsafe { arch::_subborrow_u32(borrow, a, b, out) }
34		}
35		);
36
37		// fallback for environments where we don't have a subborrow intrinsic
38		// (copied from the standard library's `borrowing_sub`)
39		#[cfg(not(any(target_arch = "x86", target_arch = "x86_64")))]
40		#[inline]
41		fn sbb(borrow: u8, lhs: BigDigit, rhs: BigDigit, out: &mut BigDigit) -> u8 {
42		let (a, b) = lhs.overflowing_sub(rhs);
43		let (c, d) = a.overflowing_sub(borrow as BigDigit);
44		*out = c;
45		u8::from(b \|\| d)
46		}
47
48	0	pub(super) fn sub2(a: &mut [BigDigit], b: &[BigDigit]) {
49	0	let mut borrow = 0;
50	0
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	0	"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	0
96	0	let borrow = __sub2rev(a_lo, b_lo);
97	0
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	0	"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_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		#[inline]
182	0	fn sub(self, mut other: BigUint) -> BigUint {
183	0	if other.data.is_empty() {
184	0	other.data.push(self as BigDigit);
185	0	} else {
186	0	sub2rev(&[self as BigDigit], &mut other.data[..]);
187	0	}
188	0	other.normalized()
189	0	}
190		);
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_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		#[inline]
213	0	fn sub_assign(&mut self, other: u64) {
214	0	sub2(&mut self.data[..], &[other as BigDigit]);
215	0	self.normalize();
216	0	}
217		);
218		}
219
220		impl Sub<BigUint> for u64 {
221		type Output = BigUint;
222
223		cfg_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		#[inline]
236	0	fn sub(self, mut other: BigUint) -> BigUint {
237	0	if other.data.is_empty() {
238	0	other.data.push(self);
239	0	} else {
240	0	sub2rev(&[self], &mut other.data[..]);
241	0	}
242	0	other.normalized()
243	0	}
244		);
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_digit!(
259		#[inline]
260		fn sub_assign(&mut self, other: u128) {
261		let (a, b, c, d) = super::u32_from_u128(other);
262		sub2(&mut self.data[..], &[d, c, b, a]);
263		self.normalize();
264		}
265
266		#[inline]
267	0	fn sub_assign(&mut self, other: u128) {
268	0	let (hi, lo) = big_digit::from_doublebigdigit(other);
269	0	sub2(&mut self.data[..], &[lo, hi]);
270	0	self.normalize();
271	0	}
272		);
273		}
274
275		impl Sub<BigUint> for u128 {
276		type Output = BigUint;
277
278		cfg_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) = super::u32_from_u128(self);
286		sub2rev(&[d, c, b, a], &mut other.data[..]);
287		other.normalized()
288		}
289
290		#[inline]
291	0	fn sub(self, mut other: BigUint) -> BigUint {
292	0	while other.data.len() < 2 {
293	0	other.data.push(0);
294	0	}
295
296	0	let (hi, lo) = big_digit::from_doublebigdigit(self);
297	0	sub2rev(&[lo, hi], &mut other.data[..]);
298	0	other.normalized()
299	0	}
300		);
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(Self::ZERO),
309	0	Greater => Some(self.sub(v)),
310		}
311	0	}
312		}