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// Copyright © 2024 Mikhail Hogrefe
//
// Uses code adopted from the GNU MP Library.
//
// Copyright © 1994, 1996, 2001, 2002, 2009-2011 Free Software Foundation, Inc.
//
// 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::integer::logic::checked_count_zeros::limbs_count_zeros_neg;
use crate::integer::Integer;
use crate::natural::logic::count_ones::limbs_count_ones;
use crate::natural::logic::hamming_distance::limbs_hamming_distance_same_length;
use crate::natural::InnerNatural::{Large, Small};
use crate::natural::Natural;
use crate::platform::Limb;
use core::cmp::Ordering;
use malachite_base::num::logic::traits::{
CheckedHammingDistance, CountOnes, CountZeros, HammingDistance,
};
use malachite_base::slices::slice_leading_zeros;
// Interpreting a slice of `Limb`s as the limbs of a `Natural` in ascending order, returns the
// Hamming distance between the negative of that `Natural` (two's complement) and the negative of a
// `Limb`. Both have infinitely many implicit leading ones. `xs` cannot be empty or only contain
// zeros; `y` cannot be zero.
//
// # Worst-case complexity
// $T(n) = O(n)$
//
// $M(n) = O(1)$
//
// where $T$ is time, $M$ is additional memory, and $n$ is `xs.len()`.
//
// # Panics
// Panics if `xs` is empty.
pub_test! {limbs_hamming_distance_limb_neg(xs: &[Limb], y: Limb) -> u64 {
let x_lo = xs[0].wrapping_neg();
limbs_count_zeros_neg(xs) - CountZeros::count_zeros(x_lo)
+ x_lo.hamming_distance(y.wrapping_neg())
}}
fn limbs_count_zeros(xs: &[Limb]) -> u64 {
xs.iter().map(|&limb| CountZeros::count_zeros(limb)).sum()
}
fn limbs_hamming_distance_neg_leading_limbs_helper(xs: &[Limb], ys: &[Limb], i: usize) -> u64 {
let xs_len = xs.len();
let ys_len = ys.len();
match xs_len.cmp(&ys_len) {
Ordering::Equal => limbs_hamming_distance_same_length(&xs[i + 1..], &ys[i + 1..]),
Ordering::Less => {
let (ys_lo, ys_hi) = ys.split_at(xs_len);
limbs_hamming_distance_same_length(&ys_lo[i + 1..], &xs[i + 1..])
+ limbs_count_ones(ys_hi)
}
Ordering::Greater => {
let (xs_lo, xs_hi) = xs.split_at(ys_len);
limbs_hamming_distance_same_length(&xs_lo[i + 1..], &ys[i + 1..])
+ limbs_count_ones(xs_hi)
}
}
}
// ```
// xs: nnnnnnnb000
// ys: nnb000000
// ```
//
// or
// ```
// xs: nnnnnb000
// ys: nnnnb000000
// ```
//
// where 0 is a zero limb, n is a nonzero limb, and b is the boundary (least-significant) nonzero
// limb. xs_i and ys_i are the indices of the boundary limbs in xs and ys. xs_i < ys_i but xs may be
// shorter, longer, or the same length as ys.
fn limbs_hamming_distance_neg_helper(xs: &[Limb], ys: &[Limb], xs_i: usize, ys_i: usize) -> u64 {
let mut distance = CountOnes::count_ones(xs[xs_i].wrapping_neg());
let xs_len = xs.len();
if xs_i == xs_len - 1 {
return distance + limbs_count_zeros_neg(&ys[xs_len..]);
}
if xs_len < ys_i {
return distance
+ limbs_count_zeros(&xs[xs_i + 1..])
+ limbs_count_zeros_neg(&ys[xs_len..]);
}
distance += limbs_count_zeros(&xs[xs_i + 1..ys_i]);
if xs_len == ys_i {
return distance + limbs_count_zeros_neg(&ys[xs_len..]);
}
distance += ys[ys_i].wrapping_neg().hamming_distance(!xs[ys_i]);
if xs_len == ys_i + 1 {
return distance + limbs_count_ones(&ys[xs_len..]);
}
distance + limbs_hamming_distance_neg_leading_limbs_helper(xs, ys, ys_i)
}
// Interpreting two equal-length slices of `Limb`s as the limbs of `Natural`s in ascending order,
// returns the Hamming distance between their negatives (two's complement). Both have infinitely
// many implicit leading ones. Neither slice may be empty or only contain zeros.
//
// # Worst-case complexity
// $T(n) = O(n)$
//
// $M(n) = O(1)$
//
// where $T$ is time, $M$ is additional memory, and $n$ is `xs.len()`.
//
// # Panics
// May panic if `xs` or `ys` only contain zeros.
//
// This is equivalent to `mpz_hamdist` from `mpz/hamdist.c`, GMP 6.2.1, where both arguments are
// negative and have the same length.
pub_test! {limbs_hamming_distance_neg(xs: &[Limb], ys: &[Limb]) -> u64 {
let xs_i = slice_leading_zeros(xs);
let ys_i = slice_leading_zeros(ys);
match xs_i.cmp(&ys_i) {
Ordering::Equal => {
xs[xs_i]
.wrapping_neg()
.hamming_distance(ys[ys_i].wrapping_neg())
+ limbs_hamming_distance_neg_leading_limbs_helper(xs, ys, xs_i)
}
Ordering::Less => limbs_hamming_distance_neg_helper(xs, ys, xs_i, ys_i),
Ordering::Greater => limbs_hamming_distance_neg_helper(ys, xs, ys_i, xs_i),
}
}}
impl Natural {
fn hamming_distance_neg_limb(&self, other: Limb) -> u64 {
match *self {
Natural(Small(small)) => small.wrapping_neg().hamming_distance(other.wrapping_neg()),
Natural(Large(ref limbs)) => limbs_hamming_distance_limb_neg(limbs, other),
}
}
fn hamming_distance_neg(&self, other: &Natural) -> u64 {
match (self, other) {
(&Natural(Small(x)), _) => other.hamming_distance_neg_limb(x),
(_, &Natural(Small(y))) => self.hamming_distance_neg_limb(y),
(&Natural(Large(ref xs)), &Natural(Large(ref ys))) => {
limbs_hamming_distance_neg(xs, ys)
}
}
}
}
impl<'a, 'b> CheckedHammingDistance<&'a Integer> for &'b Integer {
/// Determines the Hamming distance between two [`Integer`]s.
///
/// The two [`Integer`]s have infinitely many leading zeros or infinitely many leading ones,
/// depending on their signs. If they are both non-negative or both negative, the Hamming
/// distance is finite. If one is non-negative and the other is negative, the Hamming distance
/// is infinite, so `None` is returned.
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is `max(self.significant_bits(),
/// other.significant_bits())`.
///
/// # Examples
/// ```
/// use malachite_base::num::logic::traits::CheckedHammingDistance;
/// use malachite_nz::integer::Integer;
///
/// assert_eq!(Integer::from(123).checked_hamming_distance(&Integer::from(123)), Some(0));
/// // 105 = 1101001b, 123 = 1111011
/// assert_eq!(Integer::from(-105).checked_hamming_distance(&Integer::from(-123)), Some(2));
/// assert_eq!(Integer::from(-105).checked_hamming_distance(&Integer::from(123)), None);
/// ```
fn checked_hamming_distance(self, other: &Integer) -> Option<u64> {
match (self.sign, other.sign) {
(true, true) => Some(self.abs.hamming_distance(&other.abs)),
(false, false) => Some(self.abs.hamming_distance_neg(&other.abs)),
_ => None,
}
}
}