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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::{ModPowerOf2Shl, ModPowerOf2ShlAssign, UnsignedAbs};
use crate::num::basic::integers::PrimitiveInt;
use crate::num::basic::signeds::PrimitiveSigned;
use crate::num::basic::unsigneds::PrimitiveUnsigned;
use core::ops::{Shl, ShlAssign, Shr, ShrAssign};
fn mod_power_of_2_shl_unsigned<T: PrimitiveUnsigned + Shl<U, Output = T>, U: PrimitiveUnsigned>(
x: T,
other: U,
pow: u64,
) -> T {
assert!(pow <= T::WIDTH);
assert!(
x.significant_bits() <= pow,
"x must be reduced mod 2^pow, but {x} >= 2^{pow}"
);
if other >= U::exact_from(T::WIDTH) {
T::ZERO
} else {
(x << other).mod_power_of_2(pow)
}
}
fn mod_power_of_2_shl_assign_unsigned<T: PrimitiveUnsigned + ShlAssign<U>, U: PrimitiveUnsigned>(
x: &mut T,
other: U,
pow: u64,
) {
assert!(pow <= T::WIDTH);
assert!(
x.significant_bits() <= pow,
"x must be reduced mod 2^pow, but {x} >= 2^{pow}"
);
if other >= U::exact_from(T::WIDTH) {
*x = T::ZERO;
} else {
*x <<= other;
x.mod_power_of_2_assign(pow);
}
}
macro_rules! impl_mod_power_of_2_shl_unsigned {
($t:ident) => {
macro_rules! impl_mod_power_of_2_shl_unsigned_inner {
($u:ident) => {
impl ModPowerOf2Shl<$u> for $t {
type Output = $t;
/// Left-shifts a number (multiplies it by a power of 2) modulo $2^k$. The
/// number must be already reduced modulo $2^k$.
///
/// $f(x, n, k) = y$, where $x, y < 2^k$ and $2^nx \equiv y \mod 2^k$.
///
/// # Worst-case complexity
/// Constant time and additional memory.
///
/// # Panics
/// Panics if `pow` is greater than `Self::WIDTH` or if `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, other: $u, pow: u64) -> $t {
mod_power_of_2_shl_unsigned(self, other, pow)
}
}
impl ModPowerOf2ShlAssign<$u> for $t {
/// Left-shifts a number (multiplies it by a power of 2) modulo $2^k$, in place.
/// The number must be already reduced modulo $2^k$.
///
/// $x \gets y$, where $x, y < 2^k$ and $2^nx \equiv y \mod 2^k$.
///
/// # Worst-case complexity
/// Constant time and additional memory.
///
/// # Panics
/// Panics if `pow` is greater than `Self::WIDTH` or if `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, other: $u, pow: u64) {
mod_power_of_2_shl_assign_unsigned(self, other, pow);
}
}
};
}
apply_to_unsigneds!(impl_mod_power_of_2_shl_unsigned_inner);
};
}
apply_to_unsigneds!(impl_mod_power_of_2_shl_unsigned);
fn mod_power_of_2_shl_signed<
T: ModPowerOf2Shl<U, Output = T> + PrimitiveInt + Shr<U, Output = T>,
U: PrimitiveUnsigned,
S: PrimitiveSigned + UnsignedAbs<Output = U>,
>(
x: T,
other: S,
pow: u64,
) -> T {
assert!(pow <= T::WIDTH);
assert!(
x.significant_bits() <= pow,
"x must be reduced mod 2^pow, but {x} >= 2^{pow}"
);
let other_abs = other.unsigned_abs();
if other >= S::ZERO {
x.mod_power_of_2_shl(other_abs, pow)
} else {
let width = U::wrapping_from(T::WIDTH);
if width != U::ZERO && other_abs >= width {
T::ZERO
} else {
x >> other_abs
}
}
}
fn mod_power_of_2_shl_assign_signed<
T: ModPowerOf2ShlAssign<U> + PrimitiveInt + ShrAssign<U>,
U: PrimitiveUnsigned,
S: PrimitiveSigned + UnsignedAbs<Output = U>,
>(
x: &mut T,
other: S,
pow: u64,
) {
assert!(pow <= T::WIDTH);
assert!(
x.significant_bits() <= pow,
"x must be reduced mod 2^pow, but {x} >= 2^{pow}"
);
let other_abs = other.unsigned_abs();
if other >= S::ZERO {
x.mod_power_of_2_shl_assign(other_abs, pow);
} else {
let width = U::wrapping_from(T::WIDTH);
if width != U::ZERO && other_abs >= width {
*x = T::ZERO;
} else {
*x >>= other_abs;
}
}
}
macro_rules! impl_mod_power_of_2_shl_signed {
($t:ident) => {
macro_rules! impl_mod_power_of_2_shl_signed_inner {
($u:ident) => {
impl ModPowerOf2Shl<$u> for $t {
type Output = $t;
/// Left-shifts a number (multiplies it by a power of 2) modulo $2^k$. The
/// number must be already reduced modulo $2^k$.
///
/// $f(x, n, k) = y$, where $x, y < 2^k$ and $\lfloor 2^nx \rfloor \equiv y \mod
/// 2^k$.
///
/// # Panics
/// Panics if `pow` is greater than `Self::WIDTH` or if `self` is greater than
/// or equal to $2^k$.
///
/// # Worst-case complexity
/// Constant time and additional memory.
///
/// # Examples
/// See [here](super::mod_power_of_2_shl#mod_power_of_2_shl).
#[inline]
fn mod_power_of_2_shl(self, other: $u, pow: u64) -> $t {
mod_power_of_2_shl_signed(self, other, pow)
}
}
impl ModPowerOf2ShlAssign<$u> for $t {
/// Left-shifts a number (multiplies it by a power of 2) modulo $2^k$, in place.
/// The number must be already reduced modulo $2^k$.
///
/// $x \gets y$, where $x, y < 2^k$ and $\lfloor 2^nx \rfloor \equiv y \mod
/// 2^k$.
///
/// # Worst-case complexity
/// Constant time and additional memory.
///
/// # Panics
/// Panics if `pow` is greater than `Self::WIDTH` or if `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, other: $u, pow: u64) {
mod_power_of_2_shl_assign_signed(self, other, pow);
}
}
};
}
apply_to_signeds!(impl_mod_power_of_2_shl_signed_inner);
};
}
apply_to_unsigneds!(impl_mod_power_of_2_shl_signed);