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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::{ModPowerOf2, ModPowerOf2Assign};
use crate::num::basic::unsigneds::PrimitiveUnsigned;
use crate::unsigned_vector::UnsignedVector;
impl<T: PrimitiveUnsigned> ModPowerOf2 for UnsignedVector<T> {
type Output = Self;
/// Divides every element of an [`UnsignedVector`] by $2^k$, keeping the remainders, taking the
/// vector by value.
///
/// The result is reduced modulo $2^k$, which is to say that [`mod_power_of_2_is_reduced`](
/// crate::num::arithmetic::traits::ModPowerOf2IsReduced::mod_power_of_2_is_reduced) returns
/// `true` for it. The dimension is unchanged: unlike a polynomial, a vector keeps the elements
/// that reduce to zero, so $(4, 3)$ modulo 4 is $(0, 3)$.
///
/// No `T` reaches $2^W$, where $W$ is `T::WIDTH`, so for $k \geq W$ this leaves the vector
/// alone.
///
/// $$
/// f(v, k) = w, \\quad \text{where} \\quad w_i = v_i - 2^k \left \lfloor \frac{v_i}{2^k}
/// \right \rfloor.
/// $$
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is `self.dimension()`.
///
/// # Examples
/// ```
/// use core::str::FromStr;
/// use malachite_base::num::arithmetic::traits::ModPowerOf2;
/// use malachite_base::unsigned_vector::UnsignedVector;
///
/// // Every element is taken modulo 2.
/// assert_eq!(
/// UnsignedVector::<u64>::from_str("(1, 3, 2)")
/// .unwrap()
/// .mod_power_of_2(1)
/// .to_string(),
/// "(1, 1, 0)"
/// );
///
/// // An element that reduces to zero stays, so the dimension is unchanged.
/// assert_eq!(
/// UnsignedVector::<u64>::from_str("(4, 3)")
/// .unwrap()
/// .mod_power_of_2(2)
/// .to_string(),
/// "(0, 3)"
/// );
///
/// // A power at least as wide as the element type leaves the vector alone.
/// assert_eq!(
/// UnsignedVector::<u8>::from_str("(255, 1)")
/// .unwrap()
/// .mod_power_of_2(8)
/// .to_string(),
/// "(255, 1)"
/// );
/// ```
#[inline]
fn mod_power_of_2(mut self, pow: u64) -> Self {
self.mod_power_of_2_assign(pow);
self
}
}
impl<T: PrimitiveUnsigned> ModPowerOf2 for &UnsignedVector<T> {
type Output = UnsignedVector<T>;
/// Divides every element of an [`UnsignedVector`] by $2^k$, keeping the remainders, taking the
/// vector by reference.
///
/// See the documentation for the [`ModPowerOf2`] implementation on [`UnsignedVector`] for
/// details.
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(n)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is `self.dimension()`.
///
/// # Examples
/// ```
/// use core::str::FromStr;
/// use malachite_base::num::arithmetic::traits::ModPowerOf2;
/// use malachite_base::unsigned_vector::UnsignedVector;
///
/// let v = UnsignedVector::<u64>::from_str("(4, 3)").unwrap();
/// assert_eq!((&v).mod_power_of_2(2).to_string(), "(0, 3)");
/// // The vector is left alone.
/// assert_eq!(v.to_string(), "(4, 3)");
/// ```
#[inline]
fn mod_power_of_2(self, pow: u64) -> UnsignedVector<T> {
UnsignedVector {
elements: self
.elements
.iter()
.map(|&x| x.mod_power_of_2(pow))
.collect(),
}
}
}
impl<T: PrimitiveUnsigned> ModPowerOf2Assign for UnsignedVector<T> {
/// Divides every element of an [`UnsignedVector`] by $2^k$, replacing each element by the
/// remainder.
///
/// See the documentation for the [`ModPowerOf2`] implementation on [`UnsignedVector`] for
/// details.
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is `self.dimension()`.
///
/// # Examples
/// ```
/// use core::str::FromStr;
/// use malachite_base::num::arithmetic::traits::ModPowerOf2Assign;
/// use malachite_base::unsigned_vector::UnsignedVector;
///
/// let mut v = UnsignedVector::<u64>::from_str("(1, 3, 2)").unwrap();
/// v.mod_power_of_2_assign(1);
/// assert_eq!(v.to_string(), "(1, 1, 0)");
///
/// let mut v = UnsignedVector::<u64>::from_str("(4, 3)").unwrap();
/// v.mod_power_of_2_assign(2);
/// assert_eq!(v.to_string(), "(0, 3)");
/// ```
fn mod_power_of_2_assign(&mut self, pow: u64) {
// A shortcut rather than a necessity: no `T` reaches its own width as a power, so a wide
// power is already the identity on every element.
if pow >= T::WIDTH {
return;
}
for x in &mut self.elements {
x.mod_power_of_2_assign(pow);
}
}
}