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// Copyright © 2026 Mikhail Hogrefe
//
// Uses code adopted from the FLINT Library.
//
// Copyright © 2010 William Hart
//
// Copyright © 2021 Fredrik Johansson
//
// This file is part of Malachite.
//
// Malachite is free software: you can redistribute it and/or modify it under the terms of the GNU
// Lesser General Public License (LGPL) as published by the Free Software Foundation; either version
// 3 of the License, or (at your option) any later version. See <https://www.gnu.org/licenses/>.
use crate::num::arithmetic::traits::{ModSub, ModSubAssign};
use crate::num::basic::unsigneds::PrimitiveUnsigned;
fn mod_sub<T: PrimitiveUnsigned>(x: T, y: T, m: T) -> T {
assert!(x < m, "x must be reduced mod m, but {x} >= {m}");
assert!(y < m, "y must be reduced mod m, but {y} >= {m}");
let diff = x.wrapping_sub(y);
if x < y { m.wrapping_add(diff) } else { diff }
}
macro_rules! impl_mod_sub {
($t:ident) => {
impl ModSub<$t> for $t {
type Output = $t;
/// Subtracts two numbers modulo a third number $m$. The inputs must be already reduced
/// modulo $m$.
///
/// $f(x, y, m) = z$, where $x, y, z < m$ and $x - y \equiv z \mod m$.
///
/// # Worst-case complexity
/// Constant time and additional memory.
///
/// # Panics
/// Panics if `self` or `other` are greater than or equal to `m`.
///
/// # Examples
/// See [here](super::mod_sub#mod_sub).
///
/// This is equivalent to `nmod_sub` from `nmod.h`, FLINT 2.7.1.
#[inline]
fn mod_sub(self, other: $t, m: $t) -> $t {
mod_sub(self, other, m)
}
}
impl ModSubAssign<$t> for $t {
/// Subtracts two numbers modulo a third number $m$, in place. The inputs must be
/// already reduced modulo $m$.
///
/// $x \gets z$, where $x, y, z < m$ and $x - y \equiv z \mod m$.
///
/// # Worst-case complexity
/// Constant time and additional memory.
///
/// # Panics
/// Panics if `self` or `other` are greater than or equal to `m`.
///
/// # Examples
/// See [here](super::mod_sub#mod_sub_assign).
///
/// This is equivalent to `nmod_sub` from `nmod.h`, FLINT 2.7.1, where the result is
/// assigned to `a`.
#[inline]
fn mod_sub_assign(&mut self, other: $t, m: $t) {
*self = self.mod_sub(other, m);
}
}
};
}
apply_to_unsigneds!(impl_mod_sub);