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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::natural_polynomial::NaturalPolynomial;
use malachite_base::num::arithmetic::traits::{
ModPowerOf2, ModPowerOf2Assign, ModPowerOf2IsReduced, ModPowerOf2Shl, ModPowerOf2ShlAssign,
};
use malachite_base::num::basic::traits::Zero;
use malachite_base::num::conversion::traits::ExactFrom;
fn assert_reduced(p: &NaturalPolynomial, pow: u64) {
assert!(
p.mod_power_of_2_is_reduced(pow),
"self must be reduced mod 2^pow, but {p} has a coefficient >= 2^{pow}"
);
}
// Shifts every coefficient left by `bits` modulo 2^pow: only the low `pow - bits` bits of each
// survive, so a coefficient can become zero, and the result is trimmed.
fn mod_power_of_2_shl_ref(p: &NaturalPolynomial, bits: u64, pow: u64) -> NaturalPolynomial {
assert_reduced(p, pow);
if bits >= pow {
return NaturalPolynomial::ZERO;
}
let mut q = NaturalPolynomial {
coefficients: p
.coefficients
.iter()
.map(|c| c.mod_power_of_2(pow - bits) << bits)
.collect(),
};
q.trim();
q
}
fn mod_power_of_2_shl_assign(p: &mut NaturalPolynomial, bits: u64, pow: u64) {
assert_reduced(p, pow);
if bits >= pow {
*p = NaturalPolynomial::ZERO;
} else if bits != 0 {
for c in &mut p.coefficients {
c.mod_power_of_2_assign(pow - bits);
*c <<= bits;
}
p.trim();
}
}
macro_rules! impl_mod_power_of_2_shl_unsigned {
($t:ident) => {
impl ModPowerOf2Shl<$t> for NaturalPolynomial {
type Output = NaturalPolynomial;
/// Left-shifts a [`NaturalPolynomial`] (multiplies it by a power of 2) modulo $2^k$,
/// taking the polynomial by value. The coefficients must already be reduced modulo
/// $2^k$.
///
/// Every coefficient is shifted and reduced. Coefficients can become zero, so the
/// degree can drop; if `bits` is at least `pow`, the result is zero.
///
/// $$
/// f(p, m, k) = 2^mp \bmod 2^k.
/// $$
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(n)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is the number of coefficients
/// times `pow`.
///
/// # Panics
/// Panics if any coefficient 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: $t, pow: u64) -> NaturalPolynomial {
self.mod_power_of_2_shl_assign(bits, pow);
self
}
}
impl ModPowerOf2Shl<$t> for &NaturalPolynomial {
type Output = NaturalPolynomial;
/// Left-shifts a [`NaturalPolynomial`] (multiplies it by a power of 2) modulo $2^k$,
/// taking the polynomial by reference. The coefficients must already be reduced modulo
/// $2^k$.
///
/// Every coefficient is shifted and reduced. Coefficients can become zero, so the
/// degree can drop; if `bits` is at least `pow`, the result is zero.
///
/// $$
/// f(p, m, k) = 2^mp \bmod 2^k.
/// $$
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(n)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is the number of coefficients
/// times `pow`.
///
/// # Panics
/// Panics if any coefficient 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: $t, pow: u64) -> NaturalPolynomial {
mod_power_of_2_shl_ref(self, u64::exact_from(bits), pow)
}
}
impl ModPowerOf2ShlAssign<$t> for NaturalPolynomial {
/// Left-shifts a [`NaturalPolynomial`] (multiplies it by a power of 2) modulo $2^k$, in
/// place. The coefficients must already be reduced modulo $2^k$.
///
/// Every coefficient is shifted and reduced. Coefficients can become zero, so the
/// degree can drop; if `bits` is at least `pow`, the result is zero.
///
/// $$
/// p \gets 2^mp \bmod 2^k.
/// $$
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(n)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is the number of coefficients
/// times `pow`.
///
/// # Panics
/// Panics if any coefficient 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, u64::exact_from(bits), pow);
}
}
};
}
apply_to_unsigneds!(impl_mod_power_of_2_shl_unsigned);