bit-vec 0.6.3

A vector of bits
Documentation
// Copyright 2012-2020 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

// FIXME(Gankro): BitVec and BitSet are very tightly coupled. Ideally (for
// maintenance), they should be in separate files/modules, with BitSet only
// using BitVec's public API. This will be hard for performance though, because
// `BitVec` will not want to leak its internal representation while its internal
// representation as `u32`s must be assumed for best performance.

// (1) Be careful, most things can overflow here because the amount of bits in
//     memory can overflow `usize`.
// (2) Make sure that the underlying vector has no excess length:
//     E. g. `nbits == 16`, `storage.len() == 2` would be excess length,
//     because the last word isn't used at all. This is important because some
//     methods rely on it (for *CORRECTNESS*).
// (3) Make sure that the unused bits in the last word are zeroed out, again
//     other methods rely on it for *CORRECTNESS*.
// (4) `BitSet` is tightly coupled with `BitVec`, so any changes you make in
// `BitVec` will need to be reflected in `BitSet`.

//! Collections implemented with bit vectors.
//!
//! # Examples
//!
//! This is a simple example of the [Sieve of Eratosthenes][sieve]
//! which calculates prime numbers up to a given limit.
//!
//! [sieve]: http://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
//!
//! ```
//! use bit_vec::BitVec;
//!
//! let max_prime = 10000;
//!
//! // Store the primes as a BitVec
//! let primes = {
//!     // Assume all numbers are prime to begin, and then we
//!     // cross off non-primes progressively
//!     let mut bv = BitVec::from_elem(max_prime, true);
//!
//!     // Neither 0 nor 1 are prime
//!     bv.set(0, false);
//!     bv.set(1, false);
//!
//!     for i in 2.. 1 + (max_prime as f64).sqrt() as usize {
//!         // if i is a prime
//!         if bv[i] {
//!             // Mark all multiples of i as non-prime (any multiples below i * i
//!             // will have been marked as non-prime previously)
//!             for j in i.. {
//!                 if i * j >= max_prime {
//!                     break;
//!                 }
//!                 bv.set(i * j, false)
//!             }
//!         }
//!     }
//!     bv
//! };
//!
//! // Simple primality tests below our max bound
//! let print_primes = 20;
//! print!("The primes below {} are: ", print_primes);
//! for x in 0..print_primes {
//!     if primes.get(x).unwrap_or(false) {
//!         print!("{} ", x);
//!     }
//! }
//! println!();
//!
//! let num_primes = primes.iter().filter(|x| *x).count();
//! println!("There are {} primes below {}", num_primes, max_prime);
//! assert_eq!(num_primes, 1_229);
//! ```

#![doc(html_root_url = "https://docs.rs/bit-vec/0.6.3")]

#![no_std]

#[cfg(any(test, feature = "std"))]
#[macro_use]
extern crate std;
#[cfg(feature="std")]
use std::vec::Vec;

#[cfg(feature="serde")]
extern crate serde;
#[cfg(feature="serde")]
use serde::{Serialize, Deserialize};

#[cfg(not(feature="std"))]
#[macro_use]
extern crate alloc;
#[cfg(not(feature="std"))]
use alloc::vec::Vec;

use core::cmp::Ordering;
use core::cmp;
use core::fmt;
use core::hash;
use core::mem;
use core::iter::FromIterator;
use core::slice;
use core::{u8, usize};
use core::iter::repeat;
use core::ops::*;

type MutBlocks<'a, B> = slice::IterMut<'a, B>;

/// Abstracts over a pile of bits (basically unsigned primitives)
pub trait BitBlock:
	Copy +
	Add<Self, Output=Self> +
	Sub<Self, Output=Self> +
	Shl<usize, Output=Self> +
	Shr<usize, Output=Self> +
	Not<Output=Self> +
	BitAnd<Self, Output=Self> +
	BitOr<Self, Output=Self> +
	BitXor<Self, Output=Self> +
	Rem<Self, Output=Self> +
	Eq +
	Ord +
	hash::Hash
{
	/// How many bits it has
    fn bits() -> usize;
    /// How many bytes it has
    #[inline]
    fn bytes() -> usize { Self::bits() / 8 }
    /// Convert a byte into this type (lowest-order bits set)
    fn from_byte(byte: u8) -> Self;
    /// Count the number of 1's in the bitwise repr
    fn count_ones(self) -> usize;
    /// Get `0`
    fn zero() -> Self;
    /// Get `1`
    fn one() -> Self;
}

macro_rules! bit_block_impl {
    ($(($t: ident, $size: expr)),*) => ($(
        impl BitBlock for $t {
            #[inline]
            fn bits() -> usize { $size }
            #[inline]
            fn from_byte(byte: u8) -> Self { $t::from(byte) }
            #[inline]
            fn count_ones(self) -> usize { self.count_ones() as usize }
            #[inline]
            fn one() -> Self { 1 }
            #[inline]
            fn zero() -> Self { 0 }
        }
    )*)
}

bit_block_impl!{
    (u8, 8),
    (u16, 16),
    (u32, 32),
    (u64, 64),
    (usize, core::mem::size_of::<usize>() * 8)
}

fn reverse_bits(byte: u8) -> u8 {
    let mut result = 0;
    for i in 0..u8::bits() {
        result |= ((byte >> i) & 1) << (u8::bits() - 1 - i);
    }
    result
}

static TRUE: bool = true;
static FALSE: bool = false;

/// The bitvector type.
///
/// # Examples
///
/// ```
/// use bit_vec::BitVec;
///
/// let mut bv = BitVec::from_elem(10, false);
///
/// // insert all primes less than 10
/// bv.set(2, true);
/// bv.set(3, true);
/// bv.set(5, true);
/// bv.set(7, true);
/// println!("{:?}", bv);
/// println!("total bits set to true: {}", bv.iter().filter(|x| *x).count());
///
/// // flip all values in bitvector, producing non-primes less than 10
/// bv.negate();
/// println!("{:?}", bv);
/// println!("total bits set to true: {}", bv.iter().filter(|x| *x).count());
///
/// // reset bitvector to empty
/// bv.clear();
/// println!("{:?}", bv);
/// println!("total bits set to true: {}", bv.iter().filter(|x| *x).count());
/// ```
#[cfg_attr(feature="serde", derive(Serialize, Deserialize))]
pub struct BitVec<B=u32> {
    /// Internal representation of the bit vector
    storage: Vec<B>,
    /// The number of valid bits in the internal representation
    nbits: usize
}

// FIXME(Gankro): NopeNopeNopeNopeNope (wait for IndexGet to be a thing)
impl<B: BitBlock> Index<usize> for BitVec<B> {
    type Output = bool;

    #[inline]
    fn index(&self, i: usize) -> &bool {
        if self.get(i).expect("index out of bounds") {
            &TRUE
        } else {
            &FALSE
        }
    }
}

/// Computes how many blocks are needed to store that many bits
fn blocks_for_bits<B: BitBlock>(bits: usize) -> usize {
    // If we want 17 bits, dividing by 32 will produce 0. So we add 1 to make sure we
    // reserve enough. But if we want exactly a multiple of 32, this will actually allocate
    // one too many. So we need to check if that's the case. We can do that by computing if
    // bitwise AND by `32 - 1` is 0. But LLVM should be able to optimize the semantically
    // superior modulo operator on a power of two to this.
    //
    // Note that we can technically avoid this branch with the expression
    // `(nbits + U32_BITS - 1) / 32::BITS`, but if nbits is almost usize::MAX this will overflow.
    if bits % B::bits() == 0 {
        bits / B::bits()
    } else {
        bits / B::bits() + 1
    }
}

/// Computes the bitmask for the final word of the vector
fn mask_for_bits<B: BitBlock>(bits: usize) -> B {
    // Note especially that a perfect multiple of U32_BITS should mask all 1s.
    (!B::zero()) >> ((B::bits() - bits % B::bits()) % B::bits())
}

type B = u32;

impl BitVec<u32> {

    /// Creates an empty `BitVec`.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    /// let mut bv = BitVec::new();
    /// ```
    #[inline]
    pub fn new() -> Self {
        Default::default()
    }

    /// Creates a `BitVec` that holds `nbits` elements, setting each element
    /// to `bit`.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let mut bv = BitVec::from_elem(10, false);
    /// assert_eq!(bv.len(), 10);
    /// for x in bv.iter() {
    ///     assert_eq!(x, false);
    /// }
    /// ```
    #[inline]
    pub fn from_elem(nbits: usize, bit: bool) -> Self {
        let nblocks = blocks_for_bits::<B>(nbits);
        let mut bit_vec = BitVec {
            storage: vec![if bit { !B::zero() } else { B::zero() }; nblocks],
            nbits,
        };
        bit_vec.fix_last_block();
        bit_vec
    }

    /// Constructs a new, empty `BitVec` with the specified capacity.
    ///
    /// The bitvector will be able to hold at least `capacity` bits without
    /// reallocating. If `capacity` is 0, it will not allocate.
    ///
    /// It is important to note that this function does not specify the
    /// *length* of the returned bitvector, but only the *capacity*.
    #[inline]
    pub fn with_capacity(nbits: usize) -> Self {
        BitVec {
            storage: Vec::with_capacity(blocks_for_bits::<B>(nbits)),
            nbits: 0,
        }
    }

    /// Transforms a byte-vector into a `BitVec`. Each byte becomes eight bits,
    /// with the most significant bits of each byte coming first. Each
    /// bit becomes `true` if equal to 1 or `false` if equal to 0.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let bv = BitVec::from_bytes(&[0b10100000, 0b00010010]);
    /// assert!(bv.eq_vec(&[true, false, true, false,
    ///                     false, false, false, false,
    ///                     false, false, false, true,
    ///                     false, false, true, false]));
    /// ```
    pub fn from_bytes(bytes: &[u8]) -> Self {
        let len = bytes.len().checked_mul(u8::bits()).expect("capacity overflow");
        let mut bit_vec = BitVec::with_capacity(len);
        let complete_words = bytes.len() / B::bytes();
        let extra_bytes = bytes.len() % B::bytes();

        bit_vec.nbits = len;

        for i in 0..complete_words {
            let mut accumulator = B::zero();
            for idx in 0..B::bytes() {
                accumulator |=
                    B::from_byte(reverse_bits(bytes[i * B::bytes() + idx])) << (idx * 8)
            }
            bit_vec.storage.push(accumulator);
        }

        if extra_bytes > 0 {
            let mut last_word = B::zero();
            for (i, &byte) in bytes[complete_words * B::bytes()..].iter().enumerate() {
                last_word |=
                    B::from_byte(reverse_bits(byte)) << (i * 8);
            }
            bit_vec.storage.push(last_word);
        }

        bit_vec
    }

    /// Creates a `BitVec` of the specified length where the value at each index
    /// is `f(index)`.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let bv = BitVec::from_fn(5, |i| { i % 2 == 0 });
    /// assert!(bv.eq_vec(&[true, false, true, false, true]));
    /// ```
    #[inline]
    pub fn from_fn<F>(len: usize, mut f: F) -> Self
        where F: FnMut(usize) -> bool
    {
        let mut bit_vec = BitVec::from_elem(len, false);
        for i in 0..len {
            bit_vec.set(i, f(i));
        }
        bit_vec
    }
}

impl<B: BitBlock> BitVec<B> {
    /// Applies the given operation to the blocks of self and other, and sets
    /// self to be the result. This relies on the caller not to corrupt the
    /// last word.
    #[inline]
    fn process<F>(&mut self, other: &BitVec<B>, mut op: F) -> bool
    		where F: FnMut(B, B) -> B {
        assert_eq!(self.len(), other.len());
        debug_assert_eq!(self.storage.len(), other.storage.len());
        let mut changed_bits = B::zero();
        for (a, b) in self.blocks_mut().zip(other.blocks()) {
            let w = op(*a, b);
            changed_bits = changed_bits | (*a ^ w);
            *a = w;
        }
        changed_bits != B::zero()
    }

    /// Iterator over mutable refs to  the underlying blocks of data.
    #[inline]
    fn blocks_mut(&mut self) -> MutBlocks<B> {
        // (2)
        self.storage.iter_mut()
    }

    /// Iterator over the underlying blocks of data
    #[inline]
    pub fn blocks(&self) -> Blocks<B> {
        // (2)
        Blocks{iter: self.storage.iter()}
    }

    /// Exposes the raw block storage of this BitVec
    ///
    /// Only really intended for BitSet.
    #[inline]
    pub fn storage(&self) -> &[B] {
    	&self.storage
    }

    /// Exposes the raw block storage of this BitVec
    ///
    /// Can probably cause unsafety. Only really intended for BitSet.
    #[inline]
    pub unsafe fn storage_mut(&mut self) -> &mut Vec<B> {
    	&mut self.storage
    }

    /// Helper for procedures involving spare space in the last block.
    #[inline]
    fn last_block_with_mask(&self) -> Option<(B, B)> {
        let extra_bits = self.len() % B::bits();
        if extra_bits > 0 {
            let mask = (B::one() << extra_bits) - B::one();
            let storage_len = self.storage.len();
            Some((self.storage[storage_len - 1], mask))
        } else {
            None
        }
    }

    /// Helper for procedures involving spare space in the last block.
    #[inline]
    fn last_block_mut_with_mask(&mut self) -> Option<(&mut B, B)> {
        let extra_bits = self.len() % B::bits();
        if extra_bits > 0 {
            let mask = (B::one() << extra_bits) - B::one();
            let storage_len = self.storage.len();
            Some((&mut self.storage[storage_len - 1], mask))
        } else {
            None
        }
    }

    /// An operation might screw up the unused bits in the last block of the
    /// `BitVec`. As per (3), it's assumed to be all 0s. This method fixes it up.
    fn fix_last_block(&mut self) {
        if let Some((last_block, used_bits)) = self.last_block_mut_with_mask() {
            *last_block = *last_block & used_bits;
        }
    }

    /// Operations such as change detection for xnor, nor and nand are easiest
    /// to implement when unused bits are all set to 1s.
    fn fix_last_block_with_ones(&mut self) {
        if let Some((last_block, used_bits)) = self.last_block_mut_with_mask() {
            *last_block = *last_block | !used_bits;
        }
    }

    /// Check whether last block's invariant is fine.
    fn is_last_block_fixed(&self) -> bool {
        if let Some((last_block, used_bits)) = self.last_block_with_mask() {
            last_block & !used_bits == B::zero()
        } else {
            true
        }
    }

    /// Ensure the invariant for the last block.
    ///
    /// An operation might screw up the unused bits in the last block of the
    /// `BitVec`.
    ///
    /// This method fails in case the last block is not fixed. The check
    /// is skipped outside testing.
    #[inline]
    fn ensure_invariant(&self) {
        if cfg!(test) {
            debug_assert!(self.is_last_block_fixed());
        }
    }

    /// Retrieves the value at index `i`, or `None` if the index is out of bounds.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let bv = BitVec::from_bytes(&[0b01100000]);
    /// assert_eq!(bv.get(0), Some(false));
    /// assert_eq!(bv.get(1), Some(true));
    /// assert_eq!(bv.get(100), None);
    ///
    /// // Can also use array indexing
    /// assert_eq!(bv[1], true);
    /// ```
    #[inline]
    pub fn get(&self, i: usize) -> Option<bool> {
        self.ensure_invariant();
        if i >= self.nbits {
            return None;
        }
        let w = i / B::bits();
        let b = i % B::bits();
        self.storage.get(w).map(|&block|
            (block & (B::one() << b)) != B::zero()
        )
    }

    /// Sets the value of a bit at an index `i`.
    ///
    /// # Panics
    ///
    /// Panics if `i` is out of bounds.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let mut bv = BitVec::from_elem(5, false);
    /// bv.set(3, true);
    /// assert_eq!(bv[3], true);
    /// ```
    #[inline]
    pub fn set(&mut self, i: usize, x: bool) {
        self.ensure_invariant();
        assert!(i < self.nbits, "index out of bounds: {:?} >= {:?}", i, self.nbits);
        let w = i / B::bits();
        let b = i % B::bits();
        let flag = B::one() << b;
        let val = if x { self.storage[w] | flag }
                  else { self.storage[w] & !flag };
        self.storage[w] = val;
    }

    /// Sets all bits to 1.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let before = 0b01100000;
    /// let after  = 0b11111111;
    ///
    /// let mut bv = BitVec::from_bytes(&[before]);
    /// bv.set_all();
    /// assert_eq!(bv, BitVec::from_bytes(&[after]));
    /// ```
    #[inline]
    pub fn set_all(&mut self) {
        self.ensure_invariant();
        for w in &mut self.storage { *w = !B::zero(); }
        self.fix_last_block();
    }

    /// Flips all bits.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let before = 0b01100000;
    /// let after  = 0b10011111;
    ///
    /// let mut bv = BitVec::from_bytes(&[before]);
    /// bv.negate();
    /// assert_eq!(bv, BitVec::from_bytes(&[after]));
    /// ```
    #[inline]
    pub fn negate(&mut self) {
        self.ensure_invariant();
        for w in &mut self.storage { *w = !*w; }
        self.fix_last_block();
    }

    /// Calculates the union of two bitvectors. This acts like the bitwise `or`
    /// function.
    ///
    /// Sets `self` to the union of `self` and `other`. Both bitvectors must be
    /// the same length. Returns `true` if `self` changed.
    ///
    /// # Panics
    ///
    /// Panics if the bitvectors are of different lengths.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let a   = 0b01100100;
    /// let b   = 0b01011010;
    /// let res = 0b01111110;
    ///
    /// let mut a = BitVec::from_bytes(&[a]);
    /// let b = BitVec::from_bytes(&[b]);
    ///
    /// assert!(a.union(&b));
    /// assert_eq!(a, BitVec::from_bytes(&[res]));
    /// ```
    #[deprecated(
        since = "0.7.0",
        note = "Please use the 'or' function instead"
    )]
    #[inline]
    pub fn union(&mut self, other: &Self) -> bool {
        self.or(other)
    }

    /// Calculates the intersection of two bitvectors. This acts like the
    /// bitwise `and` function.
    ///
    /// Sets `self` to the intersection of `self` and `other`. Both bitvectors
    /// must be the same length. Returns `true` if `self` changed.
    ///
    /// # Panics
    ///
    /// Panics if the bitvectors are of different lengths.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let a   = 0b01100100;
    /// let b   = 0b01011010;
    /// let res = 0b01000000;
    ///
    /// let mut a = BitVec::from_bytes(&[a]);
    /// let b = BitVec::from_bytes(&[b]);
    ///
    /// assert!(a.intersect(&b));
    /// assert_eq!(a, BitVec::from_bytes(&[res]));
    /// ```
    #[deprecated(
        since = "0.7.0",
        note = "Please use the 'and' function instead"
    )]
    #[inline]
    pub fn intersect(&mut self, other: &Self) -> bool {
        self.and(other)
    }

    /// Calculates the bitwise `or` of two bitvectors.
    ///
    /// Sets `self` to the union of `self` and `other`. Both bitvectors must be
    /// the same length. Returns `true` if `self` changed.
    ///
    /// # Panics
    ///
    /// Panics if the bitvectors are of different lengths.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let a   = 0b01100100;
    /// let b   = 0b01011010;
    /// let res = 0b01111110;
    ///
    /// let mut a = BitVec::from_bytes(&[a]);
    /// let b = BitVec::from_bytes(&[b]);
    ///
    /// assert!(a.or(&b));
    /// assert_eq!(a, BitVec::from_bytes(&[res]));
    /// ```
    #[inline]
    pub fn or(&mut self, other: &Self) -> bool {
        self.ensure_invariant();
        debug_assert!(other.is_last_block_fixed());
        self.process(other, |w1, w2| (w1 | w2))
    }

    /// Calculates the bitwise `and` of two bitvectors.
    ///
    /// Sets `self` to the intersection of `self` and `other`. Both bitvectors
    /// must be the same length. Returns `true` if `self` changed.
    ///
    /// # Panics
    ///
    /// Panics if the bitvectors are of different lengths.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let a   = 0b01100100;
    /// let b   = 0b01011010;
    /// let res = 0b01000000;
    ///
    /// let mut a = BitVec::from_bytes(&[a]);
    /// let b = BitVec::from_bytes(&[b]);
    ///
    /// assert!(a.and(&b));
    /// assert_eq!(a, BitVec::from_bytes(&[res]));
    /// ```
    #[inline]
    pub fn and(&mut self, other: &Self) -> bool {
        self.ensure_invariant();
        debug_assert!(other.is_last_block_fixed());
        self.process(other, |w1, w2| (w1 & w2))
    }

    /// Calculates the difference between two bitvectors.
    ///
    /// Sets each element of `self` to the value of that element minus the
    /// element of `other` at the same index. Both bitvectors must be the same
    /// length. Returns `true` if `self` changed.
    ///
    /// # Panics
    ///
    /// Panics if the bitvectors are of different length.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let a   = 0b01100100;
    /// let b   = 0b01011010;
    /// let a_b = 0b00100100; // a - b
    /// let b_a = 0b00011010; // b - a
    ///
    /// let mut bva = BitVec::from_bytes(&[a]);
    /// let bvb = BitVec::from_bytes(&[b]);
    ///
    /// assert!(bva.difference(&bvb));
    /// assert_eq!(bva, BitVec::from_bytes(&[a_b]));
    ///
    /// let bva = BitVec::from_bytes(&[a]);
    /// let mut bvb = BitVec::from_bytes(&[b]);
    ///
    /// assert!(bvb.difference(&bva));
    /// assert_eq!(bvb, BitVec::from_bytes(&[b_a]));
    /// ```
    #[inline]
    pub fn difference(&mut self, other: &Self) -> bool {
        self.ensure_invariant();
        debug_assert!(other.is_last_block_fixed());
        self.process(other, |w1, w2| (w1 & !w2))
    }

    /// Calculates the xor of two bitvectors.
    ///
    /// Sets `self` to the xor of `self` and `other`. Both bitvectors must be
    /// the same length. Returns `true` if `self` changed.
    ///
    /// # Panics
    ///
    /// Panics if the bitvectors are of different length.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let a   = 0b01100110;
    /// let b   = 0b01010100;
    /// let res = 0b00110010;
    ///
    /// let mut a = BitVec::from_bytes(&[a]);
    /// let b = BitVec::from_bytes(&[b]);
    ///
    /// assert!(a.xor(&b));
    /// assert_eq!(a, BitVec::from_bytes(&[res]));
    /// ```
    #[inline]
    pub fn xor(&mut self, other: &Self) -> bool {
        self.ensure_invariant();
        debug_assert!(other.is_last_block_fixed());
        self.process(other, |w1, w2| (w1 ^ w2))
    }

    /// Calculates the nand of two bitvectors.
    ///
    /// Sets `self` to the nand of `self` and `other`. Both bitvectors must be
    /// the same length. Returns `true` if `self` changed.
    ///
    /// # Panics
    ///
    /// Panics if the bitvectors are of different length.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let a   = 0b01100110;
    /// let b   = 0b01010100;
    /// let res = 0b10111011;
    ///
    /// let mut a = BitVec::from_bytes(&[a]);
    /// let b = BitVec::from_bytes(&[b]);
    ///
    /// assert!(a.nand(&b));
    /// assert_eq!(a, BitVec::from_bytes(&[res]));
    /// ```
    #[inline]
    pub fn nand(&mut self, other: &Self) -> bool {
        self.ensure_invariant();
        debug_assert!(other.is_last_block_fixed());
        self.fix_last_block_with_ones();
        let result = self.process(other, |w1, w2| !(w1 & w2));
        self.fix_last_block();
        result
    }

    /// Calculates the nor of two bitvectors.
    ///
    /// Sets `self` to the nor of `self` and `other`. Both bitvectors must be
    /// the same length. Returns `true` if `self` changed.
    ///
    /// # Panics
    ///
    /// Panics if the bitvectors are of different length.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let a   = 0b01100110;
    /// let b   = 0b01010100;
    /// let res = 0b10001001;
    ///
    /// let mut a = BitVec::from_bytes(&[a]);
    /// let b = BitVec::from_bytes(&[b]);
    ///
    /// assert!(a.nor(&b));
    /// assert_eq!(a, BitVec::from_bytes(&[res]));
    /// ```
    #[inline]
    pub fn nor(&mut self, other: &Self) -> bool {
        self.ensure_invariant();
        debug_assert!(other.is_last_block_fixed());
        self.fix_last_block_with_ones();
        let result = self.process(other, |w1, w2| !(w1 | w2));
        self.fix_last_block();
        result
    }

    /// Calculates the xnor of two bitvectors.
    ///
    /// Sets `self` to the xnor of `self` and `other`. Both bitvectors must be
    /// the same length. Returns `true` if `self` changed.
    ///
    /// # Panics
    ///
    /// Panics if the bitvectors are of different length.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let a   = 0b01100110;
    /// let b   = 0b01010100;
    /// let res = 0b11001101;
    ///
    /// let mut a = BitVec::from_bytes(&[a]);
    /// let b = BitVec::from_bytes(&[b]);
    ///
    /// assert!(a.xnor(&b));
    /// assert_eq!(a, BitVec::from_bytes(&[res]));
    /// ```
    #[inline]
    pub fn xnor(&mut self, other: &Self) -> bool {
        self.ensure_invariant();
        debug_assert!(other.is_last_block_fixed());
        self.fix_last_block_with_ones();
        let result = self.process(other, |w1, w2| !(w1 ^ w2));
        self.fix_last_block();
        result
    }

    /// Returns `true` if all bits are 1.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let mut bv = BitVec::from_elem(5, true);
    /// assert_eq!(bv.all(), true);
    ///
    /// bv.set(1, false);
    /// assert_eq!(bv.all(), false);
    /// ```
    #[inline]
    pub fn all(&self) -> bool {
        self.ensure_invariant();
        let mut last_word = !B::zero();
        // Check that every block but the last is all-ones...
        self.blocks().all(|elem| {
            let tmp = last_word;
            last_word = elem;
            tmp == !B::zero()
        // and then check the last one has enough ones
        }) && (last_word == mask_for_bits(self.nbits))
    }

    /// Returns an iterator over the elements of the vector in order.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let bv = BitVec::from_bytes(&[0b01110100, 0b10010010]);
    /// assert_eq!(bv.iter().filter(|x| *x).count(), 7);
    /// ```
    #[inline]
    pub fn iter(&self) -> Iter<B> {
        self.ensure_invariant();
        Iter { bit_vec: self, range: 0..self.nbits }
    }

    /// Moves all bits from `other` into `Self`, leaving `other` empty.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let mut a = BitVec::from_bytes(&[0b10000000]);
    /// let mut b = BitVec::from_bytes(&[0b01100001]);
    ///
    /// a.append(&mut b);
    ///
    /// assert_eq!(a.len(), 16);
    /// assert_eq!(b.len(), 0);
    /// assert!(a.eq_vec(&[true, false, false, false, false, false, false, false,
    ///                    false, true, true, false, false, false, false, true]));
    /// ```
    pub fn append(&mut self, other: &mut Self) {
        self.ensure_invariant();
        debug_assert!(other.is_last_block_fixed());

        let b = self.len() % B::bits();
        let o = other.len() % B::bits();
        let will_overflow = (b + o > B::bits()) || (o == 0 && b != 0);

        self.nbits += other.len();
        other.nbits = 0;

        if b == 0 {
            self.storage.append(&mut other.storage);
        } else {
            self.storage.reserve(other.storage.len());

            for block in other.storage.drain(..) {
            	{
            		let last = self.storage.last_mut().unwrap();
                	*last = *last | (block << b);
                }
                self.storage.push(block >> (B::bits() - b));
            }

            // Remove additional block if the last shift did not overflow
            if !will_overflow {
                self.storage.pop();
            }
        }
    }

    /// Splits the `BitVec` into two at the given bit,
    /// retaining the first half in-place and returning the second one.
    ///
    /// # Panics
    ///
    /// Panics if `at` is out of bounds.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    /// let mut a = BitVec::new();
    /// a.push(true);
    /// a.push(false);
    /// a.push(false);
    /// a.push(true);
    ///
    /// let b = a.split_off(2);
    ///
    /// assert_eq!(a.len(), 2);
    /// assert_eq!(b.len(), 2);
    /// assert!(a.eq_vec(&[true, false]));
    /// assert!(b.eq_vec(&[false, true]));
    /// ```
    pub fn split_off(&mut self, at: usize) -> Self {
        self.ensure_invariant();
        assert!(at <= self.len(), "`at` out of bounds");

        let mut other = BitVec::<B>::default();

        if at == 0 {
            mem::swap(self, &mut other);
            return other;
        } else if at == self.len() {
            return other;
        }

        let w = at / B::bits();
        let b = at % B::bits();
        other.nbits = self.nbits - at;
        self.nbits = at;
        if b == 0 {
            // Split at block boundary
            other.storage = self.storage.split_off(w);
        } else {
            other.storage.reserve(self.storage.len() - w);

            {
                let mut iter = self.storage[w..].iter();
                let mut last = *iter.next().unwrap();
                for &cur in iter {
                    other.storage.push((last >> b) | (cur << (B::bits() - b)));
                    last = cur;
                }
                other.storage.push(last >> b);
            }

            self.storage.truncate(w + 1);
            self.fix_last_block();
        }

        other
    }

    /// Returns `true` if all bits are 0.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let mut bv = BitVec::from_elem(10, false);
    /// assert_eq!(bv.none(), true);
    ///
    /// bv.set(3, true);
    /// assert_eq!(bv.none(), false);
    /// ```
    #[inline]
    pub fn none(&self) -> bool {
        self.blocks().all(|w| w == B::zero())
    }

    /// Returns `true` if any bit is 1.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let mut bv = BitVec::from_elem(10, false);
    /// assert_eq!(bv.any(), false);
    ///
    /// bv.set(3, true);
    /// assert_eq!(bv.any(), true);
    /// ```
    #[inline]
    pub fn any(&self) -> bool {
        !self.none()
    }

    /// Organises the bits into bytes, such that the first bit in the
    /// `BitVec` becomes the high-order bit of the first byte. If the
    /// size of the `BitVec` is not a multiple of eight then trailing bits
    /// will be filled-in with `false`.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let mut bv = BitVec::from_elem(3, true);
    /// bv.set(1, false);
    ///
    /// assert_eq!(bv.to_bytes(), [0b10100000]);
    ///
    /// let mut bv = BitVec::from_elem(9, false);
    /// bv.set(2, true);
    /// bv.set(8, true);
    ///
    /// assert_eq!(bv.to_bytes(), [0b00100000, 0b10000000]);
    /// ```
    pub fn to_bytes(&self) -> Vec<u8> {
        self.ensure_invariant();
    	// Oh lord, we're mapping this to bytes bit-by-bit!
        fn bit<B: BitBlock>(bit_vec: &BitVec<B>, byte: usize, bit: usize) -> u8 {
            let offset = byte * 8 + bit;
            if offset >= bit_vec.nbits {
                0
            } else {
                (bit_vec[offset] as u8) << (7 - bit)
            }
        }

        let len = self.nbits / 8 +
                  if self.nbits % 8 == 0 { 0 } else { 1 };
        (0..len).map(|i|
            bit(self, i, 0) |
            bit(self, i, 1) |
            bit(self, i, 2) |
            bit(self, i, 3) |
            bit(self, i, 4) |
            bit(self, i, 5) |
            bit(self, i, 6) |
            bit(self, i, 7)
        ).collect()
    }

    /// Compares a `BitVec` to a slice of `bool`s.
    /// Both the `BitVec` and slice must have the same length.
    ///
    /// # Panics
    ///
    /// Panics if the `BitVec` and slice are of different length.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let bv = BitVec::from_bytes(&[0b10100000]);
    ///
    /// assert!(bv.eq_vec(&[true, false, true, false,
    ///                     false, false, false, false]));
    /// ```
    #[inline]
    pub fn eq_vec(&self, v: &[bool]) -> bool {
        assert_eq!(self.nbits, v.len());
        self.iter().zip(v.iter().cloned()).all(|(b1, b2)| b1 == b2)
    }

    /// Shortens a `BitVec`, dropping excess elements.
    ///
    /// If `len` is greater than the vector's current length, this has no
    /// effect.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let mut bv = BitVec::from_bytes(&[0b01001011]);
    /// bv.truncate(2);
    /// assert!(bv.eq_vec(&[false, true]));
    /// ```
    #[inline]
    pub fn truncate(&mut self, len: usize) {
        self.ensure_invariant();
        if len < self.len() {
            self.nbits = len;
            // This fixes (2).
            self.storage.truncate(blocks_for_bits::<B>(len));
            self.fix_last_block();
        }
    }

    /// Reserves capacity for at least `additional` more bits to be inserted in the given
    /// `BitVec`. The collection may reserve more space to avoid frequent reallocations.
    ///
    /// # Panics
    ///
    /// Panics if the new capacity overflows `usize`.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let mut bv = BitVec::from_elem(3, false);
    /// bv.reserve(10);
    /// assert_eq!(bv.len(), 3);
    /// assert!(bv.capacity() >= 13);
    /// ```
    #[inline]
    pub fn reserve(&mut self, additional: usize) {
        let desired_cap = self.len().checked_add(additional).expect("capacity overflow");
        let storage_len = self.storage.len();
        if desired_cap > self.capacity() {
            self.storage.reserve(blocks_for_bits::<B>(desired_cap) - storage_len);
        }
    }

    /// Reserves the minimum capacity for exactly `additional` more bits to be inserted in the
    /// given `BitVec`. Does nothing if the capacity is already sufficient.
    ///
    /// Note that the allocator may give the collection more space than it requests. Therefore
    /// capacity can not be relied upon to be precisely minimal. Prefer `reserve` if future
    /// insertions are expected.
    ///
    /// # Panics
    ///
    /// Panics if the new capacity overflows `usize`.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let mut bv = BitVec::from_elem(3, false);
    /// bv.reserve(10);
    /// assert_eq!(bv.len(), 3);
    /// assert!(bv.capacity() >= 13);
    /// ```
    #[inline]
    pub fn reserve_exact(&mut self, additional: usize) {
        let desired_cap = self.len().checked_add(additional).expect("capacity overflow");
        let storage_len = self.storage.len();
        if desired_cap > self.capacity() {
            self.storage.reserve_exact(blocks_for_bits::<B>(desired_cap) - storage_len);
        }
    }

    /// Returns the capacity in bits for this bit vector. Inserting any
    /// element less than this amount will not trigger a resizing.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let mut bv = BitVec::new();
    /// bv.reserve(10);
    /// assert!(bv.capacity() >= 10);
    /// ```
    #[inline]
    pub fn capacity(&self) -> usize {
        self.storage.capacity().checked_mul(B::bits()).unwrap_or(usize::MAX)
    }

    /// Grows the `BitVec` in-place, adding `n` copies of `value` to the `BitVec`.
    ///
    /// # Panics
    ///
    /// Panics if the new len overflows a `usize`.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let mut bv = BitVec::from_bytes(&[0b01001011]);
    /// bv.grow(2, true);
    /// assert_eq!(bv.len(), 10);
    /// assert_eq!(bv.to_bytes(), [0b01001011, 0b11000000]);
    /// ```
    pub fn grow(&mut self, n: usize, value: bool) {
        self.ensure_invariant();

        // Note: we just bulk set all the bits in the last word in this fn in multiple places
        // which is technically wrong if not all of these bits are to be used. However, at the end
        // of this fn we call `fix_last_block` at the end of this fn, which should fix this.

        let new_nbits = self.nbits.checked_add(n).expect("capacity overflow");
        let new_nblocks = blocks_for_bits::<B>(new_nbits);
        let full_value = if value { !B::zero() } else { B::zero() };

        // Correct the old tail word, setting or clearing formerly unused bits
        let num_cur_blocks = blocks_for_bits::<B>(self.nbits);
        if self.nbits % B::bits() > 0 {
            let mask = mask_for_bits::<B>(self.nbits);
            if value {
            	let block = &mut self.storage[num_cur_blocks - 1];
                *block = *block | !mask;
            } else {
                // Extra bits are already zero by invariant.
            }
        }

        // Fill in words after the old tail word
        let stop_idx = cmp::min(self.storage.len(), new_nblocks);
        for idx in num_cur_blocks..stop_idx {
            self.storage[idx] = full_value;
        }

        // Allocate new words, if needed
        if new_nblocks > self.storage.len() {
            let to_add = new_nblocks - self.storage.len();
            self.storage.extend(repeat(full_value).take(to_add));
        }

        // Adjust internal bit count
        self.nbits = new_nbits;

        self.fix_last_block();
    }

    /// Removes the last bit from the BitVec, and returns it. Returns None if the BitVec is empty.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let mut bv = BitVec::from_bytes(&[0b01001001]);
    /// assert_eq!(bv.pop(), Some(true));
    /// assert_eq!(bv.pop(), Some(false));
    /// assert_eq!(bv.len(), 6);
    /// ```
    #[inline]
    pub fn pop(&mut self) -> Option<bool> {
        self.ensure_invariant();

        if self.is_empty() {
            None
        } else {
            let i = self.nbits - 1;
            let ret = self[i];
            // (3)
            self.set(i, false);
            self.nbits = i;
            if self.nbits % B::bits() == 0 {
                // (2)
                self.storage.pop();
            }
            Some(ret)
        }
    }

    /// Pushes a `bool` onto the end.
    ///
    /// # Examples
    ///
    /// ```
    /// use bit_vec::BitVec;
    ///
    /// let mut bv = BitVec::new();
    /// bv.push(true);
    /// bv.push(false);
    /// assert!(bv.eq_vec(&[true, false]));
    /// ```
    #[inline]
    pub fn push(&mut self, elem: bool) {
        if self.nbits % B::bits() == 0 {
            self.storage.push(B::zero());
        }
        let insert_pos = self.nbits;
        self.nbits = self.nbits.checked_add(1).expect("Capacity overflow");
        self.set(insert_pos, elem);
    }

    /// Returns the total number of bits in this vector
    #[inline]
    pub fn len(&self) -> usize { self.nbits }

    /// Sets the number of bits that this BitVec considers initialized.
    ///
    /// Almost certainly can cause bad stuff. Only really intended for BitSet.
    #[inline]
    pub unsafe fn set_len(&mut self, len: usize) {
    	self.nbits = len;
    }

    /// Returns true if there are no bits in this vector
    #[inline]
    pub fn is_empty(&self) -> bool { self.len() == 0 }

    /// Clears all bits in this vector.
    #[inline]
    pub fn clear(&mut self) {
        self.ensure_invariant();
        for w in &mut self.storage { *w = B::zero(); }
    }

    /// Shrinks the capacity of the underlying storage as much as
    /// possible.
    ///
    /// It will drop down as close as possible to the length but the
    /// allocator may still inform the underlying storage that there
    /// is space for a few more elements/bits.
    pub fn shrink_to_fit(&mut self) {
        self.storage.shrink_to_fit();
    }
}

impl<B: BitBlock> Default for BitVec<B> {
    #[inline]
    fn default() -> Self { BitVec { storage: Vec::new(), nbits: 0 } }
}

impl<B: BitBlock> FromIterator<bool> for BitVec<B> {
    #[inline]
    fn from_iter<I: IntoIterator<Item=bool>>(iter: I) -> Self {
        let mut ret: Self = Default::default();
        ret.extend(iter);
        ret
    }
}

impl<B: BitBlock> Extend<bool> for BitVec<B> {
    #[inline]
    fn extend<I: IntoIterator<Item=bool>>(&mut self, iterable: I) {
        self.ensure_invariant();
        let iterator = iterable.into_iter();
        let (min, _) = iterator.size_hint();
        self.reserve(min);
        for element in iterator {
            self.push(element)
        }
    }
}

impl<B: BitBlock> Clone for BitVec<B> {
    #[inline]
    fn clone(&self) -> Self {
        self.ensure_invariant();
        BitVec { storage: self.storage.clone(), nbits: self.nbits }
    }

    #[inline]
    fn clone_from(&mut self, source: &Self) {
        debug_assert!(source.is_last_block_fixed());
        self.nbits = source.nbits;
        self.storage.clone_from(&source.storage);
    }
}

impl<B: BitBlock> PartialOrd for BitVec<B> {
    #[inline]
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

impl<B: BitBlock> Ord for BitVec<B> {
    #[inline]
    fn cmp(&self, other: &Self) -> Ordering {
        self.ensure_invariant();
        debug_assert!(other.is_last_block_fixed());
        let mut a = self.iter();
        let mut b = other.iter();
        loop {
            match (a.next(), b.next()) {
                (Some(x), Some(y)) => match x.cmp(&y) {
                    Ordering::Equal => {}
                    otherwise => return otherwise,
                },
                (None, None) => return Ordering::Equal,
                (None, _) => return Ordering::Less,
                (_, None) => return Ordering::Greater,
            }
        }
    }
}

impl<B: BitBlock> fmt::Debug for BitVec<B> {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        self.ensure_invariant();
        for bit in self {
            write!(fmt, "{}", if bit { 1 } else { 0 })?;
        }
        Ok(())
    }
}

impl<B: BitBlock> hash::Hash for BitVec<B> {
    #[inline]
    fn hash<H: hash::Hasher>(&self, state: &mut H) {
        self.ensure_invariant();
        self.nbits.hash(state);
        for elem in self.blocks() {
            elem.hash(state);
        }
    }
}

impl<B: BitBlock> cmp::PartialEq for BitVec<B> {
    #[inline]
    fn eq(&self, other: &Self) -> bool {
        if self.nbits != other.nbits {
            self.ensure_invariant();
            other.ensure_invariant();
            return false;
        }
        self.blocks().zip(other.blocks()).all(|(w1, w2)| w1 == w2)
    }
}

impl<B: BitBlock> cmp::Eq for BitVec<B> {}

/// An iterator for `BitVec`.
#[derive(Clone)]
pub struct Iter<'a, B: 'a = u32> {
    bit_vec: &'a BitVec<B>,
    range: Range<usize>,
}

impl<'a, B: BitBlock> Iterator for Iter<'a, B> {
    type Item = bool;

    #[inline]
    fn next(&mut self) -> Option<bool> {
        // NB: indexing is slow for extern crates when it has to go through &TRUE or &FALSE
        // variables.  get is more direct, and unwrap is fine since we're sure of the range.
        self.range.next().map(|i| self.bit_vec.get(i).unwrap())
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        self.range.size_hint()
    }
}

impl<'a, B: BitBlock> DoubleEndedIterator for Iter<'a, B> {
    #[inline]
    fn next_back(&mut self) -> Option<bool> {
        self.range.next_back().map(|i| self.bit_vec.get(i).unwrap())
    }
}

impl<'a, B: BitBlock> ExactSizeIterator for Iter<'a, B> {}

impl<'a, B: BitBlock> IntoIterator for &'a BitVec<B> {
    type Item = bool;
    type IntoIter = Iter<'a, B>;

    #[inline]
    fn into_iter(self) -> Iter<'a, B> {
        self.iter()
    }
}

pub struct IntoIter<B=u32> {
    bit_vec: BitVec<B>,
    range: Range<usize>,
}

impl<B: BitBlock> Iterator for IntoIter<B> {
    type Item = bool;

    #[inline]
    fn next(&mut self) -> Option<bool> {
        self.range.next().map(|i| self.bit_vec.get(i).unwrap())
    }
}

impl<B: BitBlock> DoubleEndedIterator for IntoIter<B> {
    #[inline]
    fn next_back(&mut self) -> Option<bool> {
        self.range.next_back().map(|i| self.bit_vec.get(i).unwrap())
    }
}

impl<B: BitBlock> ExactSizeIterator for IntoIter<B> {}

impl<B: BitBlock> IntoIterator for BitVec<B> {
    type Item = bool;
    type IntoIter = IntoIter<B>;

    #[inline]
    fn into_iter(self) -> IntoIter<B> {
        let nbits = self.nbits;
        IntoIter { bit_vec: self, range: 0..nbits }
    }
}

/// An iterator over the blocks of a `BitVec`.
#[derive(Clone)]
pub struct Blocks<'a, B: 'a> {
    iter: slice::Iter<'a, B>,
}

impl<'a, B: BitBlock> Iterator for Blocks<'a, B> {
    type Item = B;

    #[inline]
    fn next(&mut self) -> Option<B> {
        self.iter.next().cloned()
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
}

impl<'a, B: BitBlock> DoubleEndedIterator for Blocks<'a, B> {
    #[inline]
    fn next_back(&mut self) -> Option<B> {
        self.iter.next_back().cloned()
    }
}

impl<'a, B: BitBlock> ExactSizeIterator for Blocks<'a, B> {}

#[cfg(test)]
mod tests {
    use super::{BitVec, Iter, Vec};

    // This is stupid, but I want to differentiate from a "random" 32
    const U32_BITS: usize = 32;

    #[test]
    fn test_to_str() {
        let zerolen = BitVec::new();
        assert_eq!(format!("{:?}", zerolen), "");

        let eightbits = BitVec::from_elem(8, false);
        assert_eq!(format!("{:?}", eightbits), "00000000")
    }

    #[test]
    fn test_0_elements() {
        let act = BitVec::new();
        let exp = Vec::new();
        assert!(act.eq_vec(&exp));
        assert!(act.none() && act.all());
    }

    #[test]
    fn test_1_element() {
        let mut act = BitVec::from_elem(1, false);
        assert!(act.eq_vec(&[false]));
        assert!(act.none() && !act.all());
        act = BitVec::from_elem(1, true);
        assert!(act.eq_vec(&[true]));
        assert!(!act.none() && act.all());
    }

    #[test]
    fn test_2_elements() {
        let mut b = BitVec::from_elem(2, false);
        b.set(0, true);
        b.set(1, false);
        assert_eq!(format!("{:?}", b), "10");
        assert!(!b.none() && !b.all());
    }

    #[test]
    fn test_10_elements() {
        let mut act;
        // all 0

        act = BitVec::from_elem(10, false);
        assert!((act.eq_vec(
                    &[false, false, false, false, false, false, false, false, false, false])));
        assert!(act.none() && !act.all());
        // all 1

        act = BitVec::from_elem(10, true);
        assert!((act.eq_vec(&[true, true, true, true, true, true, true, true, true, true])));
        assert!(!act.none() && act.all());
        // mixed

        act = BitVec::from_elem(10, false);
        act.set(0, true);
        act.set(1, true);
        act.set(2, true);
        act.set(3, true);
        act.set(4, true);
        assert!((act.eq_vec(&[true, true, true, true, true, false, false, false, false, false])));
        assert!(!act.none() && !act.all());
        // mixed

        act = BitVec::from_elem(10, false);
        act.set(5, true);
        act.set(6, true);
        act.set(7, true);
        act.set(8, true);
        act.set(9, true);
        assert!((act.eq_vec(&[false, false, false, false, false, true, true, true, true, true])));
        assert!(!act.none() && !act.all());
        // mixed

        act = BitVec::from_elem(10, false);
        act.set(0, true);
        act.set(3, true);
        act.set(6, true);
        act.set(9, true);
        assert!((act.eq_vec(&[true, false, false, true, false, false, true, false, false, true])));
        assert!(!act.none() && !act.all());
    }

    #[test]
    fn test_31_elements() {
        let mut act;
        // all 0

        act = BitVec::from_elem(31, false);
        assert!(act.eq_vec(
                &[false, false, false, false, false, false, false, false, false, false, false,
                  false, false, false, false, false, false, false, false, false, false, false,
                  false, false, false, false, false, false, false, false, false]));
        assert!(act.none() && !act.all());
        // all 1

        act = BitVec::from_elem(31, true);
        assert!(act.eq_vec(
                &[true, true, true, true, true, true, true, true, true, true, true, true, true,
                  true, true, true, true, true, true, true, true, true, true, true, true, true,
                  true, true, true, true, true]));
        assert!(!act.none() && act.all());
        // mixed

        act = BitVec::from_elem(31, false);
        act.set(0, true);
        act.set(1, true);
        act.set(2, true);
        act.set(3, true);
        act.set(4, true);
        act.set(5, true);
        act.set(6, true);
        act.set(7, true);
        assert!(act.eq_vec(
                &[true, true, true, true, true, true, true, true, false, false, false, false, false,
                  false, false, false, false, false, false, false, false, false, false, false,
                  false, false, false, false, false, false, false]));
        assert!(!act.none() && !act.all());
        // mixed

        act = BitVec::from_elem(31, false);
        act.set(16, true);
        act.set(17, true);
        act.set(18, true);
        act.set(19, true);
        act.set(20, true);
        act.set(21, true);
        act.set(22, true);
        act.set(23, true);
        assert!(act.eq_vec(
                &[false, false, false, false, false, false, false, false, false, false, false,
                  false, false, false, false, false, true, true, true, true, true, true, true, true,
                  false, false, false, false, false, false, false]));
        assert!(!act.none() && !act.all());
        // mixed

        act = BitVec::from_elem(31, false);
        act.set(24, true);
        act.set(25, true);
        act.set(26, true);
        act.set(27, true);
        act.set(28, true);
        act.set(29, true);
        act.set(30, true);
        assert!(act.eq_vec(
                &[false, false, false, false, false, false, false, false, false, false, false,
                  false, false, false, false, false, false, false, false, false, false, false,
                  false, false, true, true, true, true, true, true, true]));
        assert!(!act.none() && !act.all());
        // mixed

        act = BitVec::from_elem(31, false);
        act.set(3, true);
        act.set(17, true);
        act.set(30, true);
        assert!(act.eq_vec(
                &[false, false, false, true, false, false, false, false, false, false, false, false,
                  false, false, false, false, false, true, false, false, false, false, false, false,
                  false, false, false, false, false, false, true]));
        assert!(!act.none() && !act.all());
    }

    #[test]
    fn test_32_elements() {
        let mut act;
        // all 0

        act = BitVec::from_elem(32, false);
        assert!(act.eq_vec(
                &[false, false, false, false, false, false, false, false, false, false, false,
                  false, false, false, false, false, false, false, false, false, false, false,
                  false, false, false, false, false, false, false, false, false, false]));
        assert!(act.none() && !act.all());
        // all 1

        act = BitVec::from_elem(32, true);
        assert!(act.eq_vec(
                &[true, true, true, true, true, true, true, true, true, true, true, true, true,
                  true, true, true, true, true, true, true, true, true, true, true, true, true,
                  true, true, true, true, true, true]));
        assert!(!act.none() && act.all());
        // mixed

        act = BitVec::from_elem(32, false);
        act.set(0, true);
        act.set(1, true);
        act.set(2, true);
        act.set(3, true);
        act.set(4, true);
        act.set(5, true);
        act.set(6, true);
        act.set(7, true);
        assert!(act.eq_vec(
                &[true, true, true, true, true, true, true, true, false, false, false, false, false,
                  false, false, false, false, false, false, false, false, false, false, false,
                  false, false, false, false, false, false, false, false]));
        assert!(!act.none() && !act.all());
        // mixed

        act = BitVec::from_elem(32, false);
        act.set(16, true);
        act.set(17, true);
        act.set(18, true);
        act.set(19, true);
        act.set(20, true);
        act.set(21, true);
        act.set(22, true);
        act.set(23, true);
        assert!(act.eq_vec(
                &[false, false, false, false, false, false, false, false, false, false, false,
                  false, false, false, false, false, true, true, true, true, true, true, true, true,
                  false, false, false, false, false, false, false, false]));
        assert!(!act.none() && !act.all());
        // mixed

        act = BitVec::from_elem(32, false);
        act.set(24, true);
        act.set(25, true);
        act.set(26, true);
        act.set(27, true);
        act.set(28, true);
        act.set(29, true);
        act.set(30, true);
        act.set(31, true);
        assert!(act.eq_vec(
                &[false, false, false, false, false, false, false, false, false, false, false,
                  false, false, false, false, false, false, false, false, false, false, false,
                  false, false, true, true, true, true, true, true, true, true]));
        assert!(!act.none() && !act.all());
        // mixed

        act = BitVec::from_elem(32, false);
        act.set(3, true);
        act.set(17, true);
        act.set(30, true);
        act.set(31, true);
        assert!(act.eq_vec(
                &[false, false, false, true, false, false, false, false, false, false, false, false,
                  false, false, false, false, false, true, false, false, false, false, false, false,
                  false, false, false, false, false, false, true, true]));
        assert!(!act.none() && !act.all());
    }

    #[test]
    fn test_33_elements() {
        let mut act;
        // all 0

        act = BitVec::from_elem(33, false);
        assert!(act.eq_vec(
                &[false, false, false, false, false, false, false, false, false, false, false,
                  false, false, false, false, false, false, false, false, false, false, false,
                  false, false, false, false, false, false, false, false, false, false, false]));
        assert!(act.none() && !act.all());
        // all 1

        act = BitVec::from_elem(33, true);
        assert!(act.eq_vec(
                &[true, true, true, true, true, true, true, true, true, true, true, true, true,
                  true, true, true, true, true, true, true, true, true, true, true, true, true,
                  true, true, true, true, true, true, true]));
        assert!(!act.none() && act.all());
        // mixed

        act = BitVec::from_elem(33, false);
        act.set(0, true);
        act.set(1, true);
        act.set(2, true);
        act.set(3, true);
        act.set(4, true);
        act.set(5, true);
        act.set(6, true);
        act.set(7, true);
        assert!(act.eq_vec(
                &[true, true, true, true, true, true, true, true, false, false, false, false, false,
                  false, false, false, false, false, false, false, false, false, false, false,
                  false, false, false, false, false, false, false, false, false]));
        assert!(!act.none() && !act.all());
        // mixed

        act = BitVec::from_elem(33, false);
        act.set(16, true);
        act.set(17, true);
        act.set(18, true);
        act.set(19, true);
        act.set(20, true);
        act.set(21, true);
        act.set(22, true);
        act.set(23, true);
        assert!(act.eq_vec(
                &[false, false, false, false, false, false, false, false, false, false, false,
                  false, false, false, false, false, true, true, true, true, true, true, true, true,
                  false, false, false, false, false, false, false, false, false]));
        assert!(!act.none() && !act.all());
        // mixed

        act = BitVec::from_elem(33, false);
        act.set(24, true);
        act.set(25, true);
        act.set(26, true);
        act.set(27, true);
        act.set(28, true);
        act.set(29, true);
        act.set(30, true);
        act.set(31, true);
        assert!(act.eq_vec(
                &[false, false, false, false, false, false, false, false, false, false, false,
                  false, false, false, false, false, false, false, false, false, false, false,
                  false, false, true, true, true, true, true, true, true, true, false]));
        assert!(!act.none() && !act.all());
        // mixed

        act = BitVec::from_elem(33, false);
        act.set(3, true);
        act.set(17, true);
        act.set(30, true);
        act.set(31, true);
        act.set(32, true);
        assert!(act.eq_vec(
                &[false, false, false, true, false, false, false, false, false, false, false, false,
                  false, false, false, false, false, true, false, false, false, false, false, false,
                  false, false, false, false, false, false, true, true, true]));
        assert!(!act.none() && !act.all());
    }

    #[test]
    fn test_equal_differing_sizes() {
        let v0 = BitVec::from_elem(10, false);
        let v1 = BitVec::from_elem(11, false);
        assert_ne!(v0, v1);
    }

    #[test]
    fn test_equal_greatly_differing_sizes() {
        let v0 = BitVec::from_elem(10, false);
        let v1 = BitVec::from_elem(110, false);
        assert_ne!(v0, v1);
    }

    #[test]
    fn test_equal_sneaky_small() {
        let mut a = BitVec::from_elem(1, false);
        a.set(0, true);

        let mut b = BitVec::from_elem(1, true);
        b.set(0, true);

        assert_eq!(a, b);
    }

    #[test]
    fn test_equal_sneaky_big() {
        let mut a = BitVec::from_elem(100, false);
        for i in 0..100 {
            a.set(i, true);
        }

        let mut b = BitVec::from_elem(100, true);
        for i in 0..100 {
            b.set(i, true);
        }

        assert_eq!(a, b);
    }

    #[test]
    fn test_from_bytes() {
        let bit_vec = BitVec::from_bytes(&[0b10110110, 0b00000000, 0b11111111]);
        let str = concat!("10110110", "00000000", "11111111");
        assert_eq!(format!("{:?}", bit_vec), str);
    }

    #[test]
    fn test_to_bytes() {
        let mut bv = BitVec::from_elem(3, true);
        bv.set(1, false);
        assert_eq!(bv.to_bytes(), [0b10100000]);

        let mut bv = BitVec::from_elem(9, false);
        bv.set(2, true)