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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::{ModIsReduced, ModShl, ModShlAssign};
use crate::num::basic::unsigneds::PrimitiveUnsigned;
use crate::unsigned_vector::UnsignedVector;
use crate::unsigned_vector::arithmetic::mod_mul::{mod_mul_assign_unchecked, mod_mul_unchecked};
fn assert_reduced<T: PrimitiveUnsigned>(v: &UnsignedVector<T>, m: T) {
assert!(
v.mod_is_reduced(&m),
"self must be reduced mod m, but {v} has an element >= {m}"
);
}
// Whether shifting changes nothing: a shift by 0, an empty vector, or a modulus of 1, modulo which
// every element is 0. Otherwise the vector has an element, which is less than `m`, so `m` is at
// least 2 and 1 is reduced modulo `m`.
fn is_unchanged<T: PrimitiveUnsigned, U: PrimitiveUnsigned>(
v: &UnsignedVector<T>,
bits: U,
m: T,
) -> bool {
bits == U::ZERO || v.elements.is_empty() || m == T::ONE
}
// Multiplies every element by 2^bits mod m, which is computed once.
fn mod_shl_assign<T: PrimitiveUnsigned + ModShl<U, T, Output = T>, U: PrimitiveUnsigned>(
v: &mut UnsignedVector<T>,
bits: U,
m: T,
) {
assert_reduced(v, m);
if !is_unchanged(v, bits, m) {
mod_mul_assign_unchecked(&mut v.elements, T::ONE.mod_shl(bits, m), m);
}
}
fn mod_shl_ref<T: PrimitiveUnsigned + ModShl<U, T, Output = T>, U: PrimitiveUnsigned>(
v: &UnsignedVector<T>,
bits: U,
m: T,
) -> UnsignedVector<T> {
assert_reduced(v, m);
if is_unchanged(v, bits, m) {
return v.clone();
}
UnsignedVector {
elements: mod_mul_unchecked(&v.elements, T::ONE.mod_shl(bits, m), m),
}
}
macro_rules! impl_mod_shl_unsigned {
($t:ident) => {
impl<T: PrimitiveUnsigned + ModShl<$t, T, Output = T>> ModShl<$t, T> for UnsignedVector<T> {
type Output = UnsignedVector<T>;
/// Left-shifts an [`UnsignedVector`] (multiplies it by a power of 2) modulo $m$, taking
/// the vector by value. The elements must already be reduced modulo $m$.
///
/// $2^k \bmod m$ is computed once, and every element is multiplied by it, with the data
/// for multiplying modulo $m$ also computed once. Since $m$ need not be odd, elements
/// can become zero; the dimension is unchanged.
///
/// $$
/// f(v, k, m) = 2^kv \bmod m.
/// $$
///
/// # Worst-case complexity
/// $T(n, k) = O(n + k)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, $n$ is `self.dimension()`, and $k$ is
/// `bits.significant_bits()`.
///
/// # Panics
/// Panics if `m` is 0, or if any element of `self` is greater than or equal to `m`.
///
/// # Examples
/// See [here](super::mod_shl#mod_shl).
#[inline]
fn mod_shl(mut self, bits: $t, m: T) -> UnsignedVector<T> {
mod_shl_assign(&mut self, bits, m);
self
}
}
impl<T: PrimitiveUnsigned + ModShl<$t, T, Output = T>> ModShl<$t, T>
for &UnsignedVector<T>
{
type Output = UnsignedVector<T>;
/// Left-shifts an [`UnsignedVector`] (multiplies it by a power of 2) modulo $m$, taking
/// the vector by reference. The elements must already be reduced modulo $m$.
///
/// See the documentation for the [`ModShl`] implementation that takes everything by
/// value for details.
///
/// # Worst-case complexity
/// $T(n, k) = O(n + k)$
///
/// $M(n) = O(n)$
///
/// where $T$ is time, $M$ is additional memory, $n$ is `self.dimension()`, and $k$ is
/// `bits.significant_bits()`.
///
/// # Panics
/// Panics if `m` is 0, or if any element of `self` is greater than or equal to `m`.
///
/// # Examples
/// See [here](super::mod_shl#mod_shl).
#[inline]
fn mod_shl(self, bits: $t, m: T) -> UnsignedVector<T> {
mod_shl_ref(self, bits, m)
}
}
impl<T: PrimitiveUnsigned + ModShl<$t, T, Output = T>> ModShlAssign<$t, T>
for UnsignedVector<T>
{
/// Left-shifts an [`UnsignedVector`] (multiplies it by a power of 2) modulo $m$, in
/// place. The elements must already be reduced modulo $m$.
///
/// See the documentation for the [`ModShl`] implementation that takes everything by
/// value for details.
///
/// # Worst-case complexity
/// $T(n, k) = O(n + k)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, $n$ is `self.dimension()`, and $k$ is
/// `bits.significant_bits()`.
///
/// # Panics
/// Panics if `m` is 0, or if any element of `self` is greater than or equal to `m`.
///
/// # Examples
/// See [here](super::mod_shl#mod_shl_assign).
#[inline]
fn mod_shl_assign(&mut self, bits: $t, m: T) {
mod_shl_assign(self, bits, m);
}
}
};
}
apply_to_unsigneds!(impl_mod_shl_unsigned);