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
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92

use core::ops::{Sub, SubAssign};

use crate::modular::sub::sub_montgomery_form;

use super::DynResidue;

impl<const LIMBS: usize> DynResidue<LIMBS> {
    /// Subtracts `rhs`.
    pub const fn sub(&self, rhs: &Self) -> Self {
        Self {
            montgomery_form: sub_montgomery_form(
                &self.montgomery_form,
                &rhs.montgomery_form,
                &self.residue_params.modulus,
            ),
            residue_params: self.residue_params,
        }
    }
}

impl<const LIMBS: usize> Sub<&DynResidue<LIMBS>> for &DynResidue<LIMBS> {
    type Output = DynResidue<LIMBS>;
    fn sub(self, rhs: &DynResidue<LIMBS>) -> DynResidue<LIMBS> {
        debug_assert_eq!(self.residue_params, rhs.residue_params);
        self.sub(rhs)
    }
}

impl<const LIMBS: usize> Sub<DynResidue<LIMBS>> for &DynResidue<LIMBS> {
    type Output = DynResidue<LIMBS>;
    #[allow(clippy::op_ref)]
    fn sub(self, rhs: DynResidue<LIMBS>) -> DynResidue<LIMBS> {
        self - &rhs
    }
}

impl<const LIMBS: usize> Sub<&DynResidue<LIMBS>> for DynResidue<LIMBS> {
    type Output = DynResidue<LIMBS>;
    #[allow(clippy::op_ref)]
    fn sub(self, rhs: &DynResidue<LIMBS>) -> DynResidue<LIMBS> {
        &self - rhs
    }
}

impl<const LIMBS: usize> Sub<DynResidue<LIMBS>> for DynResidue<LIMBS> {
    type Output = DynResidue<LIMBS>;
    fn sub(self, rhs: DynResidue<LIMBS>) -> DynResidue<LIMBS> {
        &self - &rhs
    }
}

impl<const LIMBS: usize> SubAssign<&DynResidue<LIMBS>> for DynResidue<LIMBS> {
    fn sub_assign(&mut self, rhs: &DynResidue<LIMBS>) {
        *self = *self - rhs;
    }
}

impl<const LIMBS: usize> SubAssign<DynResidue<LIMBS>> for DynResidue<LIMBS> {
    fn sub_assign(&mut self, rhs: DynResidue<LIMBS>) {
        *self -= &rhs;
    }
}

#[cfg(test)]
mod tests {
    use crate::{
        modular::runtime_mod::{DynResidue, DynResidueParams},
        U256,
    };

    #[test]
    fn sub_overflow() {
        let params = DynResidueParams::new(&U256::from_be_hex(
            "ffffffff00000000ffffffffffffffffbce6faada7179e84f3b9cac2fc632551",
        ));

        let x =
            U256::from_be_hex("44acf6b7e36c1342c2c5897204fe09504e1e2efb1a900377dbc4e7a6a133ec56");
        let mut x_mod = DynResidue::new(&x, params);

        let y =
            U256::from_be_hex("d5777c45019673125ad240f83094d4252d829516fac8601ed01979ec1ec1a251");
        let y_mod = DynResidue::new(&y, params);

        x_mod -= &y_mod;

        let expected =
            U256::from_be_hex("6f357a71e1d5a03167f34879d469352add829491c6df41ddff65387d7ed56f56");

        assert_eq!(expected, x_mod.retrieve());
    }
}