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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::{ModPowerOf2Dot, ModPowerOf2IsReduced};
use crate::num::basic::unsigneds::PrimitiveUnsigned;
use crate::unsigned_vector::UnsignedVector;
// The dot product of two vectors modulo $2^k$, which is the wrapping sum of the wrapping products
// with all but the lowest $k$ bits cleared, since $2^k$ divides $2^W$.
fn mod_power_of_2_dot<T: PrimitiveUnsigned>(
v: &UnsignedVector<T>,
w: &UnsignedVector<T>,
pow: u64,
) -> T {
assert!(
pow <= T::WIDTH,
"pow must be at most {}, but is {pow}",
T::WIDTH
);
assert_eq!(
v.elements.len(),
w.elements.len(),
"the vectors must have the same dimension"
);
assert!(
v.mod_power_of_2_is_reduced(pow),
"self must be reduced mod 2^{pow}, but {v} has an element >= 2^{pow}"
);
assert!(
w.mod_power_of_2_is_reduced(pow),
"other must be reduced mod 2^{pow}, but {w} has an element >= 2^{pow}"
);
let mut sum = T::ZERO;
for (&x, &y) in v.elements.iter().zip(&w.elements) {
sum.wrapping_add_assign(x.wrapping_mul(y));
}
sum.mod_power_of_2(pow)
}
impl<T: PrimitiveUnsigned> ModPowerOf2Dot<Self> for UnsignedVector<T> {
type Output = T;
/// Computes the dot product of two [`UnsignedVector`]s modulo $2^k$, taking the first by value
/// and the second by value. The elements of both must already be reduced.
///
/// The dot product of two 0-dimensional vectors is 0.
///
/// $$
/// f(v, w, k) = \sum_{i=0}^{n-1} v_iw_i \bmod 2^k,
/// $$
///
/// where $n$ is the dimension of $v$ and $w$.
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is the dimension of the vectors.
///
/// # Panics
/// Panics if `pow` is greater than `T::WIDTH`, if the vectors have different dimensions, or if
/// any element is greater than or equal to $2^k$.
///
/// # Examples
/// ```
/// use core::str::FromStr;
/// use malachite_base::num::arithmetic::traits::ModPowerOf2Dot;
/// use malachite_base::unsigned_vector::UnsignedVector;
///
/// let v = UnsignedVector::<u8>::from_str("(1, 2, 3)").unwrap();
/// let w = UnsignedVector::<u8>::from_str("(4, 5, 7)").unwrap();
/// assert_eq!(v.clone().mod_power_of_2_dot(w.clone(), 4), 3);
/// ```
#[inline]
fn mod_power_of_2_dot(self, other: Self, pow: u64) -> T {
mod_power_of_2_dot(&self, &other, pow)
}
}
impl<T: PrimitiveUnsigned> ModPowerOf2Dot<&Self> for UnsignedVector<T> {
type Output = T;
/// Computes the dot product of two [`UnsignedVector`]s modulo $2^k$, taking the first by value
/// and the second by reference. The elements of both must already be reduced.
///
/// The dot product of two 0-dimensional vectors is 0.
///
/// $$
/// f(v, w, k) = \sum_{i=0}^{n-1} v_iw_i \bmod 2^k,
/// $$
///
/// where $n$ is the dimension of $v$ and $w$.
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is the dimension of the vectors.
///
/// # Panics
/// Panics if `pow` is greater than `T::WIDTH`, if the vectors have different dimensions, or if
/// any element is greater than or equal to $2^k$.
///
/// # Examples
/// ```
/// use core::str::FromStr;
/// use malachite_base::num::arithmetic::traits::ModPowerOf2Dot;
/// use malachite_base::unsigned_vector::UnsignedVector;
///
/// let v = UnsignedVector::<u8>::from_str("(1, 2, 3)").unwrap();
/// let w = UnsignedVector::<u8>::from_str("(4, 5, 7)").unwrap();
/// assert_eq!(v.clone().mod_power_of_2_dot(&w, 4), 3);
/// ```
#[inline]
fn mod_power_of_2_dot(self, other: &Self, pow: u64) -> T {
mod_power_of_2_dot(&self, other, pow)
}
}
impl<T: PrimitiveUnsigned> ModPowerOf2Dot<UnsignedVector<T>> for &UnsignedVector<T> {
type Output = T;
/// Computes the dot product of two [`UnsignedVector`]s modulo $2^k$, taking the first by
/// reference and the second by value. The elements of both must already be reduced.
///
/// The dot product of two 0-dimensional vectors is 0.
///
/// $$
/// f(v, w, k) = \sum_{i=0}^{n-1} v_iw_i \bmod 2^k,
/// $$
///
/// where $n$ is the dimension of $v$ and $w$.
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is the dimension of the vectors.
///
/// # Panics
/// Panics if `pow` is greater than `T::WIDTH`, if the vectors have different dimensions, or if
/// any element is greater than or equal to $2^k$.
///
/// # Examples
/// ```
/// use core::str::FromStr;
/// use malachite_base::num::arithmetic::traits::ModPowerOf2Dot;
/// use malachite_base::unsigned_vector::UnsignedVector;
///
/// let v = UnsignedVector::<u8>::from_str("(1, 2, 3)").unwrap();
/// let w = UnsignedVector::<u8>::from_str("(4, 5, 7)").unwrap();
/// assert_eq!((&v).mod_power_of_2_dot(w.clone(), 4), 3);
/// ```
#[inline]
fn mod_power_of_2_dot(self, other: UnsignedVector<T>, pow: u64) -> T {
mod_power_of_2_dot(self, &other, pow)
}
}
impl<T: PrimitiveUnsigned> ModPowerOf2Dot<&UnsignedVector<T>> for &UnsignedVector<T> {
type Output = T;
/// Computes the dot product of two [`UnsignedVector`]s modulo $2^k$, taking the first by
/// reference and the second by reference. The elements of both must already be reduced.
///
/// The dot product of two 0-dimensional vectors is 0.
///
/// $$
/// f(v, w, k) = \sum_{i=0}^{n-1} v_iw_i \bmod 2^k,
/// $$
///
/// where $n$ is the dimension of $v$ and $w$.
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is the dimension of the vectors.
///
/// # Panics
/// Panics if `pow` is greater than `T::WIDTH`, if the vectors have different dimensions, or if
/// any element is greater than or equal to $2^k$.
///
/// # Examples
/// ```
/// use core::str::FromStr;
/// use malachite_base::num::arithmetic::traits::ModPowerOf2Dot;
/// use malachite_base::unsigned_vector::UnsignedVector;
///
/// let v = UnsignedVector::<u8>::from_str("(1, 2, 3)").unwrap();
/// let w = UnsignedVector::<u8>::from_str("(4, 5, 7)").unwrap();
/// assert_eq!((&v).mod_power_of_2_dot(&w, 4), 3);
/// ```
#[inline]
fn mod_power_of_2_dot(self, other: &UnsignedVector<T>, pow: u64) -> T {
mod_power_of_2_dot(self, other, pow)
}
}