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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::basic::signeds::PrimitiveSigned;
use crate::num::basic::unsigneds::PrimitiveUnsigned;
use crate::num::logic::traits::{BitScan, TrailingZeros};
fn index_of_next_false_bit_unsigned<T: PrimitiveUnsigned>(x: T, start: u64) -> u64 {
if start >= T::WIDTH {
start
} else {
TrailingZeros::trailing_zeros(!(x | T::low_mask(start)))
}
}
fn index_of_next_true_bit_unsigned<T: PrimitiveUnsigned>(x: T, start: u64) -> Option<u64> {
if start >= T::WIDTH {
None
} else {
let index = TrailingZeros::trailing_zeros(x & !T::low_mask(start));
if index == T::WIDTH { None } else { Some(index) }
}
}
macro_rules! impl_bit_scan_unsigned {
($t:ident) => {
impl BitScan for $t {
/// Given a number and a starting index, searches the number for the smallest index of a
/// `false` bit that is greater than or equal to the starting index.
///
/// Since the number is unsigned and therefore has an implicit prefix of infinitely-many
/// zeros, this function always returns a value.
///
/// Starting beyond the type's width is allowed; the result is the starting index.
///
/// # Worst-case complexity
/// Constant time and additional memory.
///
/// # Examples
/// See [here](super::bit_scan#index_of_next_false_bit).
#[inline]
fn index_of_next_false_bit(self, start: u64) -> Option<u64> {
Some(index_of_next_false_bit_unsigned(self, start))
}
/// Given a number and a starting index, searches the number for the smallest index of a
/// `true` bit that is greater than or equal to the starting index.
///
/// If the starting index is greater than or equal to the type's width, the result is
/// `None` since there are no `true` bits past that point.
///
/// # Worst-case complexity
/// Constant time and additional memory.
///
/// # Examples
/// See [here](super::bit_scan#index_of_next_true_bit).
#[inline]
fn index_of_next_true_bit(self, start: u64) -> Option<u64> {
index_of_next_true_bit_unsigned(self, start)
}
}
};
}
apply_to_unsigneds!(impl_bit_scan_unsigned);
fn index_of_next_false_bit_signed<T: PrimitiveSigned>(x: T, start: u64) -> Option<u64> {
if start >= T::WIDTH - 1 {
if x >= T::ZERO { Some(start) } else { None }
} else {
let index = TrailingZeros::trailing_zeros(!(x | T::low_mask(start)));
if index == T::WIDTH { None } else { Some(index) }
}
}
fn index_of_next_true_bit_signed<T: PrimitiveSigned>(x: T, start: u64) -> Option<u64> {
if start >= T::WIDTH - 1 {
if x >= T::ZERO { None } else { Some(start) }
} else {
let index = TrailingZeros::trailing_zeros(x & !T::low_mask(start));
if index == T::WIDTH { None } else { Some(index) }
}
}
macro_rules! impl_bit_scan_signed {
($t:ident) => {
impl BitScan for $t {
/// Given a number and a starting index, searches the number for the smallest index of a
/// `false` bit that is greater than or equal to the starting index.
///
/// If the starting index is greater than or equal to the type's width, then the result
/// depends on whether the number is negative. If it is, then the result is `None` since
/// there are no `false` bits past that point. If the number is non-negative, then the
/// result is the starting index.
///
/// # Worst-case complexity
/// Constant time and additional memory.
///
/// # Examples
/// See [here](super::bit_scan#index_of_next_false_bit).
#[inline]
fn index_of_next_false_bit(self, start: u64) -> Option<u64> {
index_of_next_false_bit_signed(self, start)
}
/// Given a number and a starting index, searches the number for the smallest index of a
/// `true` bit that is greater than or equal to the starting index.
///
/// If the starting index is greater than or equal to the type's width, then the result
/// depends on whether the number is non-negative. If it is, then the result is `None`
/// since there are no `true` bits past that point. If the number is negative, then the
/// result is the starting index.
///
/// # Worst-case complexity
/// Constant time and additional memory.
///
/// # Examples
/// See [here](super::bit_scan#index_of_next_true_bit).
#[inline]
fn index_of_next_true_bit(self, start: u64) -> Option<u64> {
index_of_next_true_bit_signed(self, start)
}
}
};
}
apply_to_signeds!(impl_bit_scan_signed);