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// Copyright © 2026 Mikhail Hogrefe
//
// 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::{ModShl, ModShlAssign, ModShr, ModShrAssign, UnsignedAbs};
use crate::num::basic::signeds::PrimitiveSigned;
use crate::num::basic::unsigneds::PrimitiveUnsigned;
use core::ops::{Shr, ShrAssign};
fn mod_shr_signed<
T: ModShl<U, T, Output = T> + PrimitiveUnsigned + Shr<U, Output = T>,
U: PrimitiveUnsigned,
S: PrimitiveSigned + UnsignedAbs<Output = U>,
>(
x: T,
other: S,
m: T,
) -> T {
assert!(x < m, "x must be reduced mod m, but {x} >= {m}");
let other_abs = other.unsigned_abs();
if other >= S::ZERO {
let width = U::wrapping_from(T::WIDTH);
if width != U::ZERO && other_abs >= width {
T::ZERO
} else {
x >> other_abs
}
} else {
x.mod_shl(other_abs, m)
}
}
fn mod_shr_assign_signed<
T: ModShlAssign<U, T> + PrimitiveUnsigned + ShrAssign<U>,
U: PrimitiveUnsigned,
S: PrimitiveSigned + UnsignedAbs<Output = U>,
>(
x: &mut T,
other: S,
m: T,
) {
assert!(*x < m, "x must be reduced mod m, but {x} >= {m}");
let other_abs = other.unsigned_abs();
if other >= S::ZERO {
let width = U::wrapping_from(T::WIDTH);
if width != U::ZERO && other_abs >= width {
*x = T::ZERO;
} else {
*x >>= other_abs;
}
} else {
x.mod_shl_assign(other_abs, m);
}
}
macro_rules! impl_mod_shr_signed {
($t:ident) => {
macro_rules! impl_mod_shr_signed_inner {
($u:ident) => {
impl ModShr<$u, $t> for $t {
type Output = $t;
/// Right-shifts a number (divides it by a power of 2) modulo a number $m$. The
/// number must be already reduced modulo $m$.
///
/// $f(x, n, m) = y$, where $x, y < m$ and $\lfloor 2^{-n}x \rfloor \equiv y
/// \mod m$.
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is
/// `other.significant_bits()`.
///
/// # Panics
/// Panics if `self` is greater than or equal to `m`.
///
/// # Examples
/// See [here](super::mod_shr#mod_shr).
#[inline]
fn mod_shr(self, other: $u, m: $t) -> $t {
mod_shr_signed(self, other, m)
}
}
impl ModShrAssign<$u, $t> for $t {
/// Right-shifts a number (divides it by a power of 2) modulo a number $m$, in
/// place. The number must be already reduced modulo $m$.
///
/// $x \gets y$, where $x, y < m$ and $\lfloor 2^{-n}x \rfloor \equiv y \mod m$.
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is
/// `other.significant_bits()`.
///
/// # Panics
/// Panics if `self` is greater than or equal to `m`.
///
/// # Examples
/// See [here](super::mod_shr#mod_shr).
#[inline]
fn mod_shr_assign(&mut self, other: $u, m: $t) {
mod_shr_assign_signed(self, other, m)
}
}
};
}
apply_to_signeds!(impl_mod_shr_signed_inner);
};
}
apply_to_unsigneds!(impl_mod_shr_signed);