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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::{ModPowerOf2IsReduced, ModPowerOf2Shl, ModPowerOf2ShlAssign};
use crate::num::basic::unsigneds::PrimitiveUnsigned;
use crate::unsigned_vector::UnsignedVector;
use alloc::vec;
fn assert_reduced<T: PrimitiveUnsigned>(v: &UnsignedVector<T>, pow: u64) {
assert!(
pow <= T::WIDTH,
"pow must be at most T::WIDTH, but it is {pow}"
);
assert!(
v.mod_power_of_2_is_reduced(pow),
"self must be reduced mod 2^pow, but {v} has an element >= 2^{pow}"
);
}
// The shift amount as a `u64`, or `None` if it is at least `pow`, in which case every element
// becomes zero. `pow` is at most `T::WIDTH`, which is at most 128, so it fits in every unsigned
// type.
fn shift_below_pow<U: PrimitiveUnsigned>(bits: U, pow: u64) -> Option<u64> {
if bits >= U::exact_from(pow) {
None
} else {
Some(bits.exact_into())
}
}
// Shifts every element left by `bits` modulo 2^pow: only the low `pow - bits` bits of each survive,
// so the shift cannot overflow.
fn mod_power_of_2_shl_ref<T: PrimitiveUnsigned, U: PrimitiveUnsigned>(
v: &UnsignedVector<T>,
bits: U,
pow: u64,
) -> UnsignedVector<T> {
assert_reduced(v, pow);
let Some(bits) = shift_below_pow(bits, pow) else {
return UnsignedVector {
elements: vec![T::ZERO; v.elements.len()],
};
};
UnsignedVector {
elements: v
.elements
.iter()
.map(|&x| x.mod_power_of_2(pow - bits) << bits)
.collect(),
}
}
fn mod_power_of_2_shl_assign<T: PrimitiveUnsigned, U: PrimitiveUnsigned>(
v: &mut UnsignedVector<T>,
bits: U,
pow: u64,
) {
assert_reduced(v, pow);
let Some(bits) = shift_below_pow(bits, pow) else {
v.elements.fill(T::ZERO);
return;
};
if bits != 0 {
for x in &mut v.elements {
*x = x.mod_power_of_2(pow - bits) << bits;
}
}
}
macro_rules! impl_mod_power_of_2_shl_unsigned {
($t:ident) => {
impl<T: PrimitiveUnsigned> ModPowerOf2Shl<$t> for UnsignedVector<T> {
type Output = UnsignedVector<T>;
/// Left-shifts an [`UnsignedVector`] (multiplies it by a power of 2) modulo $2^k$,
/// taking the vector by value. The elements must already be reduced modulo $2^k$.
///
/// Every element is shifted and reduced, and the dimension is unchanged, so elements
/// can become zero; if `bits` is at least `pow`, every element is zero.
///
/// $$
/// f(v, m, k) = 2^mv \bmod 2^k.
/// $$
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is `self.dimension()`.
///
/// # Panics
/// Panics if `pow` is greater than `T::WIDTH`, or if any element of `self` is greater
/// than or equal to $2^k$.
///
/// # Examples
/// See [here](super::mod_power_of_2_shl#mod_power_of_2_shl).
#[inline]
fn mod_power_of_2_shl(mut self, bits: $t, pow: u64) -> UnsignedVector<T> {
self.mod_power_of_2_shl_assign(bits, pow);
self
}
}
impl<T: PrimitiveUnsigned> ModPowerOf2Shl<$t> for &UnsignedVector<T> {
type Output = UnsignedVector<T>;
/// Left-shifts an [`UnsignedVector`] (multiplies it by a power of 2) modulo $2^k$,
/// taking the vector by reference. The elements must already be reduced modulo $2^k$.
///
/// See the documentation for the [`ModPowerOf2Shl`] implementation that takes the
/// vector by value 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()`.
///
/// # Panics
/// Panics if `pow` is greater than `T::WIDTH`, or if any element of `self` is greater
/// than or equal to $2^k$.
///
/// # Examples
/// See [here](super::mod_power_of_2_shl#mod_power_of_2_shl).
#[inline]
fn mod_power_of_2_shl(self, bits: $t, pow: u64) -> UnsignedVector<T> {
mod_power_of_2_shl_ref(self, bits, pow)
}
}
impl<T: PrimitiveUnsigned> ModPowerOf2ShlAssign<$t> for UnsignedVector<T> {
/// Left-shifts an [`UnsignedVector`] (multiplies it by a power of 2) modulo $2^k$, in
/// place. The elements must already be reduced modulo $2^k$.
///
/// See the documentation for the [`ModPowerOf2Shl`] implementation that takes the
/// vector by value 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()`.
///
/// # Panics
/// Panics if `pow` is greater than `T::WIDTH`, or if any element of `self` is greater
/// than or equal to $2^k$.
///
/// # Examples
/// See [here](super::mod_power_of_2_shl#mod_power_of_2_shl_assign).
#[inline]
fn mod_power_of_2_shl_assign(&mut self, bits: $t, pow: u64) {
mod_power_of_2_shl_assign(self, bits, pow);
}
}
};
}
apply_to_unsigneds!(impl_mod_power_of_2_shl_unsigned);