malachite_base/num/arithmetic/
mod_sub_mul.rs

1// Copyright © 2026 Mikhail Hogrefe
2//
3// This file is part of Malachite.
4//
5// Malachite is free software: you can redistribute it and/or modify it under the terms of the GNU
6// Lesser General Public License (LGPL) as published by the Free Software Foundation; either version
7// 3 of the License, or (at your option) any later version. See <https://www.gnu.org/licenses/>.
8
9use crate::num::arithmetic::traits::{ModSubMul, ModSubMulAssign};
10use crate::num::basic::unsigneds::PrimitiveUnsigned;
11
12fn assert_reduced<T: PrimitiveUnsigned>(x: T, y: T, z: T, m: T) {
13    assert!(x < m, "x must be reduced mod m, but {x} >= {m}");
14    assert!(y < m, "y must be reduced mod m, but {y} >= {m}");
15    assert!(z < m, "z must be reduced mod m, but {z} >= {m}");
16}
17
18#[inline]
19fn mod_sub_mul<T: PrimitiveUnsigned>(x: T, y: T, z: T, m: T) -> T {
20    assert_reduced(x, y, z, m);
21    x.mod_sub(y.mod_mul(z, m), m)
22}
23
24#[inline]
25fn mod_sub_mul_assign<T: PrimitiveUnsigned>(x: &mut T, y: T, z: T, m: T) {
26    assert_reduced(*x, y, z, m);
27    x.mod_sub_assign(y.mod_mul(z, m), m);
28}
29
30macro_rules! impl_mod_sub_mul {
31    ($t:ident) => {
32        impl ModSubMul<$t> for $t {
33            type Output = $t;
34
35            /// Subtracts the product of two numbers from a third number, modulo a fourth number
36            /// $m$. All three inputs must be already reduced modulo $m$.
37            ///
38            /// $f(x, y, z, m) = w$, where $x, y, z, w < m$ and $x - yz \equiv w \mod m$.
39            ///
40            /// # Worst-case complexity
41            /// Constant time and additional memory.
42            ///
43            /// # Panics
44            /// Panics if `self`, `y`, or `z` are greater than or equal to `m`.
45            ///
46            /// # Examples
47            /// See [here](super::mod_sub_mul#mod_sub_mul).
48            #[inline]
49            fn mod_sub_mul(self, y: $t, z: $t, m: $t) -> $t {
50                mod_sub_mul(self, y, z, m)
51            }
52        }
53
54        impl ModSubMulAssign<$t> for $t {
55            /// Subtracts the product of two numbers from a third number, modulo a fourth number
56            /// $m$, in place. All three inputs must be already reduced modulo $m$.
57            ///
58            /// $x \gets w$, where $x, y, z, w < m$ and $x - yz \equiv w \mod m$.
59            ///
60            /// # Worst-case complexity
61            /// Constant time and additional memory.
62            ///
63            /// # Panics
64            /// Panics if `self`, `y`, or `z` are greater than or equal to `m`.
65            ///
66            /// # Examples
67            /// See [here](super::mod_sub_mul#mod_sub_mul_assign).
68            #[inline]
69            fn mod_sub_mul_assign(&mut self, y: $t, z: $t, m: $t) {
70                mod_sub_mul_assign(self, y, z, m);
71            }
72        }
73    };
74}
75apply_to_unsigneds!(impl_mod_sub_mul);
malachite_base/num/arithmetic/mod_sub_mul.rs

malachite_base/num/arithmetic/
mod_sub_mul.rs
