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// Copyright © 2024 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::conversion::to_limbs::LimbIterator;
use crate::natural::Natural;
use crate::platform::Limb;
use core::ops::Index;
use malachite_base::num::arithmetic::traits::PowerOf2;
use malachite_base::num::basic::integers::PrimitiveInt;
use malachite_base::num::conversion::traits::ExactFrom;
use malachite_base::num::logic::traits::{BitAccess, BitIterable, SignificantBits};
/// A double-ended iterator over the bits of a [`Natural`].
///
/// The forward order is ascending (least-significant first).
///
/// This `struct` is created by [`BitIterable::bits`]; see its documentation for more.
#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
pub struct NaturalBitIterator<'a> {
pub(crate) significant_bits: u64,
pub(crate) limbs: LimbIterator<'a>,
remaining: usize,
indices_are_in_same_limb: bool,
current_limb_forward: Limb,
current_limb_back: Limb,
// If `n` is nonzero, this mask initially points to the least-significant bit, and is left-
// shifted by next().
i_mask: Limb,
// If `n` is nonzero, this mask initially points to the most-significant nonzero bit, and is
// right-shifted by next_back().
j_mask: Limb,
}
impl<'a> Iterator for NaturalBitIterator<'a> {
type Item = bool;
fn next(&mut self) -> Option<bool> {
if self.remaining != 0 {
let bit = self.current_limb_forward & self.i_mask != 0;
self.i_mask <<= 1;
if self.i_mask == 0 {
self.i_mask = 1;
if let Some(next) = self.limbs.next() {
self.current_limb_forward = next;
} else {
self.current_limb_forward = self.current_limb_back;
self.indices_are_in_same_limb = true;
}
}
self.remaining -= 1;
Some(bit)
} else {
None
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
(self.remaining, Some(self.remaining))
}
}
impl<'a> DoubleEndedIterator for NaturalBitIterator<'a> {
fn next_back(&mut self) -> Option<bool> {
if self.remaining != 0 {
let bit = self.current_limb_back & self.j_mask != 0;
self.j_mask >>= 1;
if self.j_mask == 0 {
self.j_mask = Limb::power_of_2(Limb::WIDTH - 1);
if let Some(next_back) = self.limbs.next_back() {
self.current_limb_back = next_back;
} else {
self.current_limb_back = self.current_limb_forward;
self.indices_are_in_same_limb = true;
}
}
self.remaining -= 1;
Some(bit)
} else {
None
}
}
}
impl<'a> ExactSizeIterator for NaturalBitIterator<'a> {}
impl<'a> Index<u64> for NaturalBitIterator<'a> {
type Output = bool;
/// A function to retrieve a [`Natural`]'s bits by index.
///
/// The index is the power of 2 of which the bit is a coefficient. Indexing at or above the
/// significant bit count returns `false` bits.
///
/// This is equivalent to [`get_bit`](malachite_base::num::logic::traits::BitAccess::get_bit).
///
/// # Worst-case complexity
/// Constant time and additional memory.
///
/// # Examples
/// ```
/// use malachite_base::num::basic::traits::Zero;
/// use malachite_base::num::logic::traits::BitIterable;
/// use malachite_nz::natural::Natural;
///
/// assert_eq!(Natural::ZERO.bits()[0], false);
///
/// // 105 = 1101001b
/// let n = Natural::from(105u32);
/// let bits = n.bits();
/// assert_eq!(bits[0], true);
/// assert_eq!(bits[1], false);
/// assert_eq!(bits[2], false);
/// assert_eq!(bits[3], true);
/// assert_eq!(bits[4], false);
/// assert_eq!(bits[5], true);
/// assert_eq!(bits[6], true);
/// assert_eq!(bits[7], false);
/// assert_eq!(bits[100], false);
/// ```
fn index(&self, index: u64) -> &bool {
if self.limbs.n.get_bit(index) {
&true
} else {
&false
}
}
}
impl<'a> BitIterable for &'a Natural {
type BitIterator = NaturalBitIterator<'a>;
/// Returns a double-ended iterator over the bits of a [`Natural`].
///
/// The forward order is ascending, so that less significant bits appear first. There are no
/// trailing false bits going forward, or leading falses going backward.
///
/// If it's necessary to get a [`Vec`] of all the bits, consider using
/// [`to_bits_asc`](malachite_base::num::logic::traits::BitConvertible::to_bits_asc) or
/// [`to_bits_desc`](malachite_base::num::logic::traits::BitConvertible::to_bits_desc) instead.
///
/// # Worst-case complexity
/// Constant time and additional memory.
///
/// # Examples
/// ```
/// use malachite_base::num::basic::traits::Zero;
/// use malachite_base::num::logic::traits::BitIterable;
/// use malachite_nz::natural::Natural;
///
/// assert!(Natural::ZERO.bits().next().is_none());
/// // 105 = 1101001b
/// assert_eq!(
/// Natural::from(105u32).bits().collect::<Vec<bool>>(),
/// &[true, false, false, true, false, true, true]
/// );
///
/// assert!(Natural::ZERO.bits().next_back().is_none());
/// // 105 = 1101001b
/// assert_eq!(
/// Natural::from(105u32).bits().rev().collect::<Vec<bool>>(),
/// &[true, true, false, true, false, false, true]
/// );
/// ```
fn bits(self) -> NaturalBitIterator<'a> {
let significant_bits = self.significant_bits();
let remainder = significant_bits & Limb::WIDTH_MASK;
let mut bits = NaturalBitIterator {
significant_bits,
limbs: self.limbs(),
remaining: usize::exact_from(significant_bits),
indices_are_in_same_limb: significant_bits <= Limb::WIDTH,
current_limb_forward: 0,
current_limb_back: 0,
i_mask: 1,
j_mask: if remainder != 0 {
Limb::power_of_2(remainder - 1)
} else {
Limb::power_of_2(Limb::WIDTH - 1)
},
};
if let Some(next) = bits.limbs.next() {
bits.current_limb_forward = next;
}
if let Some(next_back) = bits.limbs.next_back() {
bits.current_limb_back = next_back;
} else {
bits.current_limb_back = bits.current_limb_forward;
}
bits
}
}