1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
//! Two's complement negation wrapping at 2^256.
use super::U256;
impl U256 {
/// Computes the two's complement negation `2^256 - self`, wrapping on
/// overflow (i.e., negating zero returns zero).
///
/// This is equivalent to `(!self).overflowing_add(&ONE).0` but computed
/// via `ZERO.overflowing_sub(self)` for clarity.
///
/// # Examples
///
/// ```
/// use cnfy_uint::u256::U256;
///
/// let p = U256::from_be_limbs([
/// 0xFFFFFFFFFFFFFFFF,
/// 0xFFFFFFFFFFFFFFFF,
/// 0xFFFFFFFFFFFFFFFF,
/// 0xFFFFFFFEFFFFFC2F,
/// ]);
/// let complement = p.negate();
/// assert_eq!(complement, U256::from_be_limbs([0, 0, 0, 0x1000003D1]));
/// ```
#[inline]
pub const fn negate(&self) -> U256 {
U256::ZERO.overflowing_sub(self).0
}
}
#[cfg(test)]
mod ai_tests {
use super::*;
/// Negating zero returns zero.
#[test]
fn neg_zero() {
assert_eq!(U256::ZERO.negate(), U256::ZERO);
}
/// Negating one returns 2^256 - 1 (all bits set).
#[test]
fn neg_one() {
assert_eq!(
U256::ONE.negate(),
U256::from_be_limbs([u64::MAX, u64::MAX, u64::MAX, u64::MAX]),
);
}
/// Double negation is identity.
#[test]
fn double_neg() {
let a = U256::from_be_limbs([0x1234, 0x5678, 0x9ABC, 0xDEF0]);
assert_eq!(a.negate().negate(), a);
}
/// Negation of secp256k1 P equals P_COMPLEMENT.
#[test]
fn neg_p() {
let p = U256::from_be_limbs([
0xFFFFFFFF_FFFFFFFF,
0xFFFFFFFF_FFFFFFFF,
0xFFFFFFFF_FFFFFFFF,
0xFFFFFFFE_FFFFFC2F,
]);
let p_complement = U256::from_be_limbs([0, 0, 0, 0x1000003D1]);
assert_eq!(p.negate(), p_complement);
}
/// x + (-x) wraps to zero.
#[test]
fn add_neg_is_zero() {
let a = U256::from_be_limbs([0xAB, 0xCD, 0xEF, 0x42]);
let (sum, _) = a.overflowing_add(&a.negate());
assert_eq!(sum, U256::ZERO);
}
}