use crate::logic::*;
use crate::{CLog2, SafeDivCeil};
use itertools::izip;
use std::num::NonZeroU8;
use std::ops::{BitAnd, BitAndAssign, BitOr, BitOrAssign};

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub(super) enum OpResult {
    Unchanged,
    Changed,
}

impl BitAnd for OpResult {
    type Output = Self;

    #[inline]
    fn bitand(self, rhs: Self) -> Self::Output {
        match (self, rhs) {
            (Self::Changed, Self::Changed) => Self::Changed,
            _ => Self::Unchanged,
        }
    }
}

impl BitAndAssign for OpResult {
    #[inline]
    fn bitand_assign(&mut self, rhs: Self) {
        *self = *self & rhs;
    }
}

impl BitOr for OpResult {
    type Output = Self;

    #[inline]
    fn bitor(self, rhs: Self) -> Self::Output {
        match (self, rhs) {
            (Self::Unchanged, Self::Unchanged) => Self::Unchanged,
            _ => Self::Changed,
        }
    }
}

impl BitOrAssign for OpResult {
    #[inline]
    fn bitor_assign(&mut self, rhs: Self) {
        *self = *self | rhs;
    }
}

// SAFETY:
// These functions are on the hot path of the simulation,
// so it is important to optimize them as much as possible.
// Therefore in release mode we turn off all bounds checks
// and assume our invariants hold. This is technically not
// safe so proper testing in debug mode is required.

#[cfg(not(debug_assertions))]
macro_rules! get {
    ($slice:expr, $i:expr) => {
        unsafe { *$slice.get_unchecked($i) }
    };
}

#[cfg(debug_assertions)]
macro_rules! get {
    ($slice:expr, $i:expr) => {
        $slice[$i]
    };
}

#[cfg(not(debug_assertions))]
macro_rules! get_mut {
    ($slice:expr, $i:expr) => {
        unsafe { $slice.get_unchecked_mut($i) }
    };
}

#[cfg(debug_assertions)]
macro_rules! get_mut {
    ($slice:expr, $i:expr) => {
        &mut $slice[$i]
    };
}

#[inline]
fn perform_3<Op>(
    width: NonZeroU8,
    out: &mut [Atom],
    lhs: &[Atom],
    rhs: &[Atom],
    mut op: Op,
) -> OpResult
where
    Op: FnMut(AtomWidth, Atom, Atom) -> Atom,
{
    debug_assert_eq!(out.len(), width.safe_div_ceil(Atom::BITS).get() as usize);
    debug_assert_eq!(out.len(), lhs.len());
    debug_assert_eq!(out.len(), rhs.len());

    let mut result = OpResult::Unchanged;

    let mut i = 0;
    let mut total_width = width.get();
    while total_width >= Atom::BITS.get() {
        let out = get_mut!(out, i);
        let lhs = get!(lhs, i);
        let rhs = get!(rhs, i);

        let new = op(AtomWidth::MAX, lhs, rhs);
        if !out.eq(new, AtomWidth::MAX) {
            result = OpResult::Changed;
        }
        *out = new;

        i += 1;
        total_width -= Atom::BITS.get();
    }

    if total_width > 0 {
        let last_out = get_mut!(out, i);
        let last_lhs = get!(lhs, i);
        let last_rhs = get!(rhs, i);

        let last_width = unsafe {
            // SAFETY: the loop and if condition ensure that 0 < total_width < Atom::BITS
            AtomWidth::new_unchecked(total_width)
        };

        let last_new = op(last_width, last_lhs, last_rhs);
        if !last_out.eq(last_new, last_width) {
            result = OpResult::Changed;
        }
        *last_out = last_new;
    }

    result
}

#[inline]
fn perform_2<Op>(width: NonZeroU8, out: &mut [Atom], rhs: &[Atom], mut op: Op) -> OpResult
where
    Op: FnMut(AtomWidth, Atom, Atom) -> Atom,
{
    debug_assert_eq!(out.len(), width.safe_div_ceil(Atom::BITS).get() as usize);
    debug_assert_eq!(out.len(), rhs.len());

    let mut result = OpResult::Unchanged;

    let mut i = 0;
    let mut total_width = width.get();
    while total_width >= Atom::BITS.get() {
        let out = get_mut!(out, i);
        let rhs = get!(rhs, i);

        let new = op(AtomWidth::MAX, *out, rhs);
        if !out.eq(new, AtomWidth::MAX) {
            result = OpResult::Changed;
        }
        *out = new;

        i += 1;
        total_width -= Atom::BITS.get();
    }

    if total_width > 0 {
        let last_out = get_mut!(out, i);
        let last_rhs = get!(rhs, i);

        let last_width = unsafe {
            // SAFETY: the loop and if condition ensure that 0 < total_width < Atom::BITS
            AtomWidth::new_unchecked(total_width)
        };

        let last_new = op(last_width, *last_out, last_rhs);
        if !last_out.eq(last_new, last_width) {
            result = OpResult::Changed;
        }
        *last_out = last_new;
    }

    result
}

#[inline]
fn perform_1<Op>(width: NonZeroU8, out: &mut [Atom], mut op: Op) -> OpResult
where
    Op: FnMut(AtomWidth, Atom) -> Atom,
{
    debug_assert_eq!(out.len(), width.safe_div_ceil(Atom::BITS).get() as usize);

    let mut result = OpResult::Unchanged;

    let mut i = 0;
    let mut total_width = width.get();
    while total_width >= Atom::BITS.get() {
        let out = get_mut!(out, i);

        let new = op(AtomWidth::MAX, *out);
        if !out.eq(new, AtomWidth::MAX) {
            result = OpResult::Changed;
        }
        *out = new;

        i += 1;
        total_width -= Atom::BITS.get();
    }

    if total_width > 0 {
        let last_out = get_mut!(out, i);

        let last_width = unsafe {
            // SAFETY: the loop and if condition ensure that 0 < total_width < Atom::BITS
            AtomWidth::new_unchecked(total_width)
        };

        let last_new = op(last_width, *last_out);
        if !last_out.eq(last_new, last_width) {
            result = OpResult::Changed;
        }
        *last_out = last_new;
    }

    result
}

#[inline]
fn logic_and_impl(a: Atom, b: Atom) -> Atom {
    //  A state | A valid | A meaning | B state | B valid | B meaning | O state | O valid | O meaning
    // ---------|---------|-----------|---------|---------|-----------|---------|---------|-----------
    //     0    |    0    | High-Z    |    0    |    0    | High-Z    |    1    |    0    | Undefined
    //     1    |    0    | Undefined |    0    |    0    | High-Z    |    1    |    0    | Undefined
    //     0    |    1    | Logic 0   |    0    |    0    | High-Z    |    0    |    1    | Logic 0
    //     1    |    1    | Logic 1   |    0    |    0    | High-Z    |    1    |    0    | Undefined
    //     0    |    0    | High-Z    |    1    |    0    | Undefined |    1    |    0    | Undefined
    //     1    |    0    | Undefined |    1    |    0    | Undefined |    1    |    0    | Undefined
    //     0    |    1    | Logic 0   |    1    |    0    | Undefined |    0    |    1    | Logic 0
    //     1    |    1    | Logic 1   |    1    |    0    | Undefined |    1    |    0    | Undefined
    //     0    |    0    | High-Z    |    0    |    1    | Logic 0   |    0    |    1    | Logic 0
    //     1    |    0    | Undefined |    0    |    1    | Logic 0   |    0    |    1    | Logic 0
    //     0    |    1    | Logic 0   |    0    |    1    | Logic 0   |    0    |    1    | Logic 0
    //     1    |    1    | Logic 1   |    0    |    1    | Logic 0   |    0    |    1    | Logic 0
    //     0    |    0    | High-Z    |    1    |    1    | Logic 1   |    1    |    0    | Undefined
    //     1    |    0    | Undefined |    1    |    1    | Logic 1   |    1    |    0    | Undefined
    //     0    |    1    | Logic 0   |    1    |    1    | Logic 1   |    0    |    1    | Logic 0
    //     1    |    1    | Logic 1   |    1    |    1    | Logic 1   |    1    |    1    | Logic 1

    Atom {
        state: (a.state & b.state)
            | (!a.valid & !b.valid)
            | (a.state & !b.valid)
            | (b.state & !a.valid),
        valid: (a.valid & b.valid) | (!a.state & a.valid) | (!b.state & b.valid),
    }
}

#[inline]
fn logic_or_impl(a: Atom, b: Atom) -> Atom {
    //  A state | A valid | A meaning | B state | B valid | B meaning | O state | O valid | O meaning
    // ---------|---------|-----------|---------|---------|-----------|---------|---------|-----------
    //     0    |    0    | High-Z    |    0    |    0    | High-Z    |    1    |    0    | Undefined
    //     1    |    0    | Undefined |    0    |    0    | High-Z    |    1    |    0    | Undefined
    //     0    |    1    | Logic 0   |    0    |    0    | High-Z    |    1    |    0    | Undefined
    //     1    |    1    | Logic 1   |    0    |    0    | High-Z    |    1    |    1    | Logic 1
    //     0    |    0    | High-Z    |    1    |    0    | Undefined |    1    |    0    | Undefined
    //     1    |    0    | Undefined |    1    |    0    | Undefined |    1    |    0    | Undefined
    //     0    |    1    | Logic 0   |    1    |    0    | Undefined |    1    |    0    | Undefined
    //     1    |    1    | Logic 1   |    1    |    0    | Undefined |    1    |    1    | Logic 1
    //     0    |    0    | High-Z    |    0    |    1    | Logic 0   |    1    |    0    | Undefined
    //     1    |    0    | Undefined |    0    |    1    | Logic 0   |    1    |    0    | Undefined
    //     0    |    1    | Logic 0   |    0    |    1    | Logic 0   |    0    |    1    | Logic 0
    //     1    |    1    | Logic 1   |    0    |    1    | Logic 0   |    1    |    1    | Logic 1
    //     0    |    0    | High-Z    |    1    |    1    | Logic 1   |    1    |    1    | Logic 1
    //     1    |    0    | Undefined |    1    |    1    | Logic 1   |    1    |    1    | Logic 1
    //     0    |    1    | Logic 0   |    1    |    1    | Logic 1   |    1    |    1    | Logic 1
    //     1    |    1    | Logic 1   |    1    |    1    | Logic 1   |    1    |    1    | Logic 1

    Atom {
        state: a.state | !a.valid | b.state | !b.valid,
        valid: (a.state & a.valid) | (b.state & b.valid) | (a.valid & b.valid),
    }
}

#[inline]
fn logic_xor_impl(a: Atom, b: Atom) -> Atom {
    //  A state | A valid | A meaning | B state | B valid | B meaning | O state | O valid | O meaning
    // ---------|---------|-----------|---------|---------|-----------|---------|---------|-----------
    //     0    |    0    | High-Z    |    0    |    0    | High-Z    |    1    |    0    | Undefined
    //     1    |    0    | Undefined |    0    |    0    | High-Z    |    1    |    0    | Undefined
    //     0    |    1    | Logic 0   |    0    |    0    | High-Z    |    1    |    0    | Undefined
    //     1    |    1    | Logic 1   |    0    |    0    | High-Z    |    1    |    0    | Undefined
    //     0    |    0    | High-Z    |    1    |    0    | Undefined |    1    |    0    | Undefined
    //     1    |    0    | Undefined |    1    |    0    | Undefined |    1    |    0    | Undefined
    //     0    |    1    | Logic 0   |    1    |    0    | Undefined |    1    |    0    | Undefined
    //     1    |    1    | Logic 1   |    1    |    0    | Undefined |    1    |    0    | Undefined
    //     0    |    0    | High-Z    |    0    |    1    | Logic 0   |    1    |    0    | Undefined
    //     1    |    0    | Undefined |    0    |    1    | Logic 0   |    1    |    0    | Undefined
    //     0    |    1    | Logic 0   |    0    |    1    | Logic 0   |    0    |    1    | Logic 0
    //     1    |    1    | Logic 1   |    0    |    1    | Logic 0   |    1    |    1    | Logic 1
    //     0    |    0    | High-Z    |    1    |    1    | Logic 1   |    1    |    0    | Undefined
    //     1    |    0    | Undefined |    1    |    1    | Logic 1   |    1    |    0    | Undefined
    //     0    |    1    | Logic 0   |    1    |    1    | Logic 1   |    1    |    1    | Logic 1
    //     1    |    1    | Logic 1   |    1    |    1    | Logic 1   |    0    |    1    | Logic 0

    Atom {
        state: (a.state ^ b.state) | !a.valid | !b.valid,
        valid: a.valid & b.valid,
    }
}

#[inline]
fn logic_nand_impl(a: Atom, b: Atom) -> Atom {
    //  A state | A valid | A meaning | B state | B valid | B meaning | O state | O valid | O meaning
    // ---------|---------|-----------|---------|---------|-----------|---------|---------|-----------
    //     0    |    0    | High-Z    |    0    |    0    | High-Z    |    1    |    0    | Undefined
    //     1    |    0    | Undefined |    0    |    0    | High-Z    |    1    |    0    | Undefined
    //     0    |    1    | Logic 0   |    0    |    0    | High-Z    |    1    |    1    | Logic 1
    //     1    |    1    | Logic 1   |    0    |    0    | High-Z    |    1    |    0    | Undefined
    //     0    |    0    | High-Z    |    1    |    0    | Undefined |    1    |    0    | Undefined
    //     1    |    0    | Undefined |    1    |    0    | Undefined |    1    |    0    | Undefined
    //     0    |    1    | Logic 0   |    1    |    0    | Undefined |    1    |    1    | Logic 1
    //     1    |    1    | Logic 1   |    1    |    0    | Undefined |    1    |    0    | Undefined
    //     0    |    0    | High-Z    |    0    |    1    | Logic 0   |    1    |    1    | Logic 1
    //     1    |    0    | Undefined |    0    |    1    | Logic 0   |    1    |    1    | Logic 1
    //     0    |    1    | Logic 0   |    0    |    1    | Logic 0   |    1    |    1    | Logic 1
    //     1    |    1    | Logic 1   |    0    |    1    | Logic 0   |    1    |    1    | Logic 1
    //     0    |    0    | High-Z    |    1    |    1    | Logic 1   |    1    |    0    | Undefined
    //     1    |    0    | Undefined |    1    |    1    | Logic 1   |    1    |    0    | Undefined
    //     0    |    1    | Logic 0   |    1    |    1    | Logic 1   |    1    |    1    | Logic 1
    //     1    |    1    | Logic 1   |    1    |    1    | Logic 1   |    0    |    1    | Logic 0

    Atom {
        state: !a.state | !a.valid | !b.state | !b.valid,
        valid: (a.valid & b.valid) | (!a.state & a.valid) | (!b.state & b.valid),
    }
}

#[inline]
fn logic_nor_impl(a: Atom, b: Atom) -> Atom {
    //  A state | A valid | A meaning | B state | B valid | B meaning | O state | O valid | O meaning
    // ---------|---------|-----------|---------|---------|-----------|---------|---------|-----------
    //     0    |    0    | High-Z    |    0    |    0    | High-Z    |    1    |    0    | Undefined
    //     1    |    0    | Undefined |    0    |    0    | High-Z    |    1    |    0    | Undefined
    //     0    |    1    | Logic 0   |    0    |    0    | High-Z    |    1    |    0    | Undefined
    //     1    |    1    | Logic 1   |    0    |    0    | High-Z    |    0    |    1    | Logic 0
    //     0    |    0    | High-Z    |    1    |    0    | Undefined |    1    |    0    | Undefined
    //     1    |    0    | Undefined |    1    |    0    | Undefined |    1    |    0    | Undefined
    //     0    |    1    | Logic 0   |    1    |    0    | Undefined |    1    |    0    | Undefined
    //     1    |    1    | Logic 1   |    1    |    0    | Undefined |    0    |    1    | Logic 0
    //     0    |    0    | High-Z    |    0    |    1    | Logic 0   |    1    |    0    | Undefined
    //     1    |    0    | Undefined |    0    |    1    | Logic 0   |    1    |    0    | Undefined
    //     0    |    1    | Logic 0   |    0    |    1    | Logic 0   |    1    |    1    | Logic 1
    //     1    |    1    | Logic 1   |    0    |    1    | Logic 0   |    0    |    1    | Logic 0
    //     0    |    0    | High-Z    |    1    |    1    | Logic 1   |    0    |    1    | Logic 0
    //     1    |    0    | Undefined |    1    |    1    | Logic 1   |    0    |    1    | Logic 0
    //     0    |    1    | Logic 0   |    1    |    1    | Logic 1   |    0    |    1    | Logic 0
    //     1    |    1    | Logic 1   |    1    |    1    | Logic 1   |    0    |    1    | Logic 0

    Atom {
        state: (!a.state & !b.state)
            | (!a.valid & !b.valid)
            | (!a.state & !b.valid)
            | (!b.state & !a.valid),
        valid: (a.state & a.valid) | (b.state & b.valid) | (a.valid & b.valid),
    }
}

#[inline]
fn logic_xnor_impl(a: Atom, b: Atom) -> Atom {
    //  A state | A valid | A meaning | B state | B valid | B meaning | O state | O valid | O meaning
    // ---------|---------|-----------|---------|---------|-----------|---------|---------|-----------
    //     0    |    0    | High-Z    |    0    |    0    | High-Z    |    1    |    0    | Undefined
    //     1    |    0    | Undefined |    0    |    0    | High-Z    |    1    |    0    | Undefined
    //     0    |    1    | Logic 0   |    0    |    0    | High-Z    |    1    |    0    | Undefined
    //     1    |    1    | Logic 1   |    0    |    0    | High-Z    |    1    |    0    | Undefined
    //     0    |    0    | High-Z    |    1    |    0    | Undefined |    1    |    0    | Undefined
    //     1    |    0    | Undefined |    1    |    0    | Undefined |    1    |    0    | Undefined
    //     0    |    1    | Logic 0   |    1    |    0    | Undefined |    1    |    0    | Undefined
    //     1    |    1    | Logic 1   |    1    |    0    | Undefined |    1    |    0    | Undefined
    //     0    |    0    | High-Z    |    0    |    1    | Logic 0   |    1    |    0    | Undefined
    //     1    |    0    | Undefined |    0    |    1    | Logic 0   |    1    |    0    | Undefined
    //     0    |    1    | Logic 0   |    0    |    1    | Logic 0   |    1    |    1    | Logic 1
    //     1    |    1    | Logic 1   |    0    |    1    | Logic 0   |    0    |    1    | Logic 0
    //     0    |    0    | High-Z    |    1    |    1    | Logic 1   |    1    |    0    | Undefined
    //     1    |    0    | Undefined |    1    |    1    | Logic 1   |    1    |    0    | Undefined
    //     0    |    1    | Logic 0   |    1    |    1    | Logic 1   |    0    |    1    | Logic 0
    //     1    |    1    | Logic 1   |    1    |    1    | Logic 1   |    1    |    1    | Logic 1

    Atom {
        state: !(a.state ^ b.state) | !a.valid | !b.valid,
        valid: a.valid & b.valid,
    }
}

macro_rules! def_binary_op {
    ($op_impl:ident -> $name3:ident, $name2:ident) => {
        pub(super) fn $name3(
            width: NonZeroU8,
            out: &mut [Atom],
            lhs: &[Atom],
            rhs: &[Atom],
        ) -> OpResult {
            perform_3(width, out, lhs, rhs, |_, a, b| $op_impl(a, b))
        }

        #[allow(dead_code)]
        pub(super) fn $name2(width: NonZeroU8, out: &mut [Atom], rhs: &[Atom]) -> OpResult {
            perform_2(width, out, rhs, |_, a, b| $op_impl(a, b))
        }
    };
}

def_binary_op!(logic_and_impl -> logic_and_3, logic_and_2);
def_binary_op!(logic_or_impl -> logic_or_3, logic_or_2);
def_binary_op!(logic_xor_impl -> logic_xor_3, logic_xor_2);
def_binary_op!(logic_nand_impl -> logic_nand_3, logic_nand_2);
def_binary_op!(logic_nor_impl -> logic_nor_3, logic_nor_2);
def_binary_op!(logic_xnor_impl -> logic_xnor_3, logic_xnor_2);

#[inline]
fn logic_not_impl(v: Atom) -> Atom {
    //  I state | I valid | I meaning | O state | O valid | O meaning
    // ---------|---------|-----------|---------|---------|-----------
    //     0    |    0    | High-Z    |    1    |    0    | Undefined
    //     1    |    0    | Undefined |    1    |    0    | Undefined
    //     0    |    1    | Logic 0   |    1    |    1    | Logic 1
    //     1    |    1    | Logic 1   |    0    |    1    | Logic 0

    Atom {
        state: !v.state | !v.valid,
        valid: v.valid,
    }
}

macro_rules! def_unary_op {
    ($op_impl:ident -> $name2:ident, $name1:ident) => {
        pub(super) fn $name2(width: NonZeroU8, out: &mut [Atom], val: &[Atom]) -> OpResult {
            perform_2(width, out, val, |_, _, v| $op_impl(v))
        }

        pub(super) fn $name1(width: NonZeroU8, out: &mut [Atom]) -> OpResult {
            perform_1(width, out, |_, v| $op_impl(v))
        }
    };
}

def_unary_op!(logic_not_impl -> logic_not_2, logic_not_1);

pub(super) fn buffer(
    width: NonZeroU8,
    out: &mut [Atom],
    val: &[Atom],
    en: LogicBitState,
) -> OpResult {
    match en {
        LogicBitState::Undefined => perform_1(width, out, |_, _| Atom::UNDEFINED),
        LogicBitState::Logic1 => perform_2(width, out, val, |_, _, v| v.high_z_to_undefined()),
        _ => perform_1(width, out, |_, _| Atom::HIGH_Z),
    }
}

#[inline]
fn add_impl(width: AtomWidth, a: Atom, b: Atom, c: LogicBitState) -> (Atom, LogicBitState) {
    let (c_in, c_valid) = c.to_bits();
    let sum = (a.state.get() as u64) + (b.state.get() as u64) + (c_in as u64);

    let valid_mask_a = a.valid.keep_trailing_ones();
    let valid_mask_b = b.valid.keep_trailing_ones();
    let valid_mask_c = match c_valid {
        false => LogicStorage::ALL_ZERO,
        true => LogicStorage::ALL_ONE,
    };
    let valid_mask = (valid_mask_a & valid_mask_b & valid_mask_c).get();

    let c_valid = (valid_mask >> (width.get() - 1)) > 0;
    let c_state = ((sum >> width.get()) > 0) | !c_valid;

    (
        Atom {
            state: LogicStorage::new((sum as u32) | !valid_mask),
            valid: LogicStorage::new(valid_mask),
        },
        LogicBitState::from_bits(c_state, c_valid),
    )
}

pub(super) fn add(
    width: NonZeroU8,
    out: &mut [Atom],
    carry_out: &mut LogicBitState,
    lhs: &[Atom],
    rhs: &[Atom],
    carry_in: LogicBitState,
) -> OpResult {
    let mut carry = carry_in;
    let result = perform_3(width, out, lhs, rhs, |width, a, b| {
        let sum;
        (sum, carry) = add_impl(width, a, b, carry);
        sum
    });

    *carry_out = carry;
    result
}

pub(super) fn sub(
    width: NonZeroU8,
    out: &mut [Atom],
    carry_out: &mut LogicBitState,
    lhs: &[Atom],
    rhs: &[Atom],
    carry_in: LogicBitState,
) -> OpResult {
    let mut carry = carry_in;
    let result = perform_3(width, out, lhs, rhs, |width, a, mut b| {
        let sum;
        b.state = !b.state;
        (sum, carry) = add_impl(width, a, b, carry);
        sum
    });

    *carry_out = carry;
    result
}

pub(super) fn neg(
    width: NonZeroU8,
    out: &mut [Atom],
    carry_out: &mut LogicBitState,
    val: &[Atom],
    carry_in: LogicBitState,
) -> OpResult {
    let mut carry = carry_in;
    let result = perform_2(width, out, val, |width, _, mut v| {
        let sum;
        v.state = !v.state;
        (sum, carry) = add_impl(width, Atom::LOGIC_0, v, carry);
        sum
    });

    *carry_out = carry;
    result
}

#[inline]
fn mul_impl(width: AtomWidth, prev: Atom, a: Atom, b: Atom, c: Atom) -> (Atom, Atom) {
    let mask = LogicStorage::mask(width);

    let prev_valid = prev.valid | !mask;
    let a_valid = a.valid | !mask;
    let b_valid = b.valid | !mask;
    let c_valid = c.valid | !mask;

    if (prev_valid != LogicStorage::ALL_ONE)
        | (a_valid != LogicStorage::ALL_ONE)
        | (b_valid != LogicStorage::ALL_ONE)
        | (c_valid != LogicStorage::ALL_ONE)
    {
        return (Atom::UNDEFINED, Atom::UNDEFINED);
    }

    let prev_state = prev.state & mask;
    let a_state = a.state & mask;
    let b_state = b.state & mask;
    let c_state = c.state & mask;

    let product = (prev_state.get() as u64)
        + (a_state.get() as u64) * (b_state.get() as u64)
        + (c_state.get() as u64);

    (
        Atom::from_int(product as u32),
        Atom::from_int((product >> 32) as u32),
    )
}

pub(super) fn mul(width: NonZeroU8, out: &mut [Atom], lhs: &[Atom], rhs: &[Atom]) -> OpResult {
    debug_assert_eq!(out.len(), width.safe_div_ceil(Atom::BITS).get() as usize);
    debug_assert_eq!(out.len(), lhs.len());
    debug_assert_eq!(out.len(), rhs.len());

    let mut tmp_state = [Atom::LOGIC_0; MAX_ATOM_COUNT];
    let tmp_state = get_mut!(tmp_state, ..out.len());

    let mut total_width = width.get();
    for (i, lhs) in lhs.iter().copied().enumerate() {
        let width = AtomWidth::new(total_width).unwrap_or(AtomWidth::MAX);
        total_width -= width.get();

        let mut carry = Atom::LOGIC_0;
        for (j, rhs) in rhs.iter().copied().enumerate() {
            if let Some(dst) = tmp_state.get_mut(i + j) {
                (*dst, carry) = mul_impl(width, *dst, lhs, rhs, carry);
            } else {
                break;
            }
        }
    }

    let mut iter = tmp_state.iter().copied();
    perform_1(width, out, |_, _| iter.next().unwrap())
}

//#[inline]
//pub(super) fn div(a: Atom, b: Atom, width: LogicWidth) -> Atom {
//    let mask = LogicStorage::mask(width);
//    let a_state = a.state & mask;
//    let b_state = b.state & mask;
//    let a_valid = a.valid | !mask;
//    let b_valid = b.valid | !mask;
//
//    if (a_valid == LogicStorage::ALL_ONE)
//        && (b_valid == LogicStorage::ALL_ONE)
//        && (b_state != LogicStorage::ALL_ZERO)
//    {
//        Atom {
//            state: a_state / b_state,
//            valid: LogicStorage::ALL_ONE,
//        }
//    } else {
//        Atom::UNDEFINED
//    }
//}
//
//#[inline]
//pub(super) fn rem(a: Atom, b: Atom, width: LogicWidth) -> Atom {
//    let mask = LogicStorage::mask(width);
//    let a_state = a.state & mask;
//    let b_state = b.state & mask;
//    let a_valid = a.valid | !mask;
//    let b_valid = b.valid | !mask;
//
//    if (a_valid == LogicStorage::ALL_ONE)
//        && (b_valid == LogicStorage::ALL_ONE)
//        && (b_state != LogicStorage::ALL_ZERO)
//    {
//        Atom {
//            state: a_state % b_state,
//            valid: LogicStorage::ALL_ONE,
//        }
//    } else {
//        Atom::UNDEFINED
//    }
//}

#[inline]
fn perform_shift<'a, Iter, F>(
    width: NonZeroU8,
    shamnt_width: NonZeroU8,
    out: &mut [Atom],
    val: &'a [Atom],
    shamnt: Atom,
    make_iter: F,
) -> OpResult
where
    Iter: Iterator<Item = Atom>,
    F: FnOnce(NonZeroU8, &'a [Atom], usize) -> Iter + 'a,
{
    debug_assert_eq!(width.clog2(), shamnt_width.get());
    debug_assert!(shamnt_width <= Atom::BITS);

    let shamnt_width = unsafe { AtomWidth::new_unchecked(shamnt_width.get()) };
    if shamnt.is_valid(shamnt_width) {
        debug_assert_eq!(out.len(), width.safe_div_ceil(Atom::BITS).get() as usize);
        debug_assert_eq!(out.len(), val.len());

        let shamnt_mask = LogicStorage::mask(shamnt_width);
        let shamnt = (shamnt.state & shamnt_mask).get() as usize;

        let mut result = OpResult::Unchanged;

        let mut i = 0;
        let mut total_width = width.get();
        let mut val_iter = make_iter(width, val, shamnt);
        while total_width >= Atom::BITS.get() {
            let out = get_mut!(out, i);
            let val = val_iter.next().unwrap();

            if !out.eq(val, AtomWidth::MAX) {
                result = OpResult::Changed;
            }
            *out = val;

            i += 1;
            total_width -= Atom::BITS.get();
        }

        if total_width > 0 {
            let last_out = get_mut!(out, i);
            let last_val = val_iter.next().unwrap();

            let last_width = unsafe {
                // SAFETY: the loop and if condition ensure that 0 < total_width < Atom::BITS
                AtomWidth::new_unchecked(total_width)
            };

            if !last_out.eq(last_val, last_width) {
                result = OpResult::Changed;
            }
            *last_out = last_val;
        }

        result
    } else {
        perform_1(width, out, |_, _| Atom::UNDEFINED)
    }
}

struct ShlIter<'a> {
    iter: std::slice::Iter<'a, Atom>,
    atom_shift: usize,
    bit_shift: AtomOffset,
    carry: Option<Atom>,
}

impl<'a> ShlIter<'a> {
    #[inline]
    fn new(val: &'a [Atom], shamnt: usize) -> Self {
        let atom_shift = shamnt / (Atom::BITS.get() as usize);
        let bit_shift = unsafe {
            // SAFETY: <anything> % 32 = [0..31]
            AtomOffset::new_unchecked((shamnt % (Atom::BITS.get() as usize)) as u8)
        };

        Self {
            iter: val.iter(),
            atom_shift,
            bit_shift,
            carry: None,
        }
    }
}

impl Iterator for ShlIter<'_> {
    type Item = Atom;

    #[inline]
    fn next(&mut self) -> Option<Self::Item> {
        if self.atom_shift > 0 {
            self.atom_shift -= 1;
            Some(Atom::LOGIC_0)
        } else if let Some(next) = self.iter.next().copied().map(Atom::high_z_to_undefined) {
            let (low_state, high_state) = next.state.widening_shl(self.bit_shift);
            let (low_valid, high_valid) = next.valid.widening_shl(self.bit_shift);
            let carry = self.carry.unwrap_or(Atom {
                state: Atom::LOGIC_0.state.widening_shl(self.bit_shift).1,
                valid: Atom::LOGIC_0.valid.widening_shl(self.bit_shift).1,
            });

            self.carry = Some(Atom {
                state: high_state,
                valid: high_valid,
            });

            Some(Atom {
                state: low_state | carry.state,
                valid: low_valid | carry.valid,
            })
        } else if let Some(carry) = self.carry.take() {
            Some(carry)
        } else {
            Some(Atom::LOGIC_0)
        }
    }
}

pub(super) fn shl(
    width: NonZeroU8,
    shamnt_width: NonZeroU8,
    out: &mut [Atom],
    val: &[Atom],
    shamnt: Atom,
) -> OpResult {
    perform_shift(width, shamnt_width, out, val, shamnt, |_, val, shamnt| {
        ShlIter::new(val, shamnt)
    })
}

struct MaskingIter<Iter: Iterator<Item = Atom>> {
    width: u8,
    fill: Atom,
    iter: Iter,
}

impl<Iter: Iterator<Item = Atom>> MaskingIter<Iter> {
    #[inline]
    fn new(width: NonZeroU8, fill: Atom, iter: Iter) -> Self {
        Self {
            width: width.get(),
            fill,
            iter,
        }
    }
}

impl<Iter: Iterator<Item = Atom>> Iterator for MaskingIter<Iter> {
    type Item = Atom;

    #[inline]
    fn next(&mut self) -> Option<Self::Item> {
        if self.width > 0 {
            let next = self.iter.next().unwrap_or(self.fill);

            let width = AtomWidth::new(self.width).unwrap_or(AtomWidth::MAX);
            self.width -= width.get();

            let mask = LogicStorage::mask(width);
            let inv_mask = !mask;

            Some(Atom {
                state: (next.state & mask) | (self.fill.state & inv_mask),
                valid: (next.valid & mask) | (self.fill.valid & inv_mask),
            })
        } else {
            Some(self.fill)
        }
    }
}

struct ShrIter<'a> {
    iter: MaskingIter<std::iter::Copied<std::iter::Skip<std::slice::Iter<'a, Atom>>>>,
    bit_shift: AtomOffset,
    current: Atom,
}

impl<'a> ShrIter<'a> {
    #[inline]
    fn new_logical(width: NonZeroU8, val: &'a [Atom], shamnt: usize) -> Self {
        let atom_shift = shamnt / (Atom::BITS.get() as usize);
        let bit_shift = unsafe {
            // SAFETY: <anything> % 32 = [0..31]
            AtomOffset::new_unchecked((shamnt % (Atom::BITS.get() as usize)) as u8)
        };

        let mut iter = MaskingIter::new(width, Atom::LOGIC_0, val.iter().skip(atom_shift).copied());
        let current = iter.next().map(Atom::high_z_to_undefined).unwrap();
        let current = Atom {
            state: current.state >> bit_shift,
            valid: current.valid >> bit_shift,
        };

        Self {
            iter,
            bit_shift,
            current,
        }
    }

    #[inline]
    fn new_arithmetic(width: NonZeroU8, val: &'a [Atom], shamnt: usize) -> Self {
        let atom_index = ((width.get() - 1) / Atom::BITS.get()) as usize;
        let bit_index = unsafe {
            // SAFETY: <anything> % 32 = [0..31]
            AtomOffset::new_unchecked((width.get() - 1) % Atom::BITS.get())
        };

        let atom_shift = shamnt / (Atom::BITS.get() as usize);
        let bit_shift = unsafe {
            // SAFETY: <anything> % 32 = [0..31]
            AtomOffset::new_unchecked((shamnt % (Atom::BITS.get() as usize)) as u8)
        };

        let fill = val[atom_index].get_bit_state(bit_index).splat();
        let mut iter = MaskingIter::new(width, fill, val.iter().skip(atom_shift).copied());
        let current = iter.next().map(Atom::high_z_to_undefined).unwrap();
        let current = Atom {
            state: current.state >> bit_shift,
            valid: current.valid >> bit_shift,
        };

        Self {
            iter,
            bit_shift,
            current,
        }
    }
}

impl Iterator for ShrIter<'_> {
    type Item = Atom;

    #[inline]
    fn next(&mut self) -> Option<Self::Item> {
        let current = self.current;
        let next = self.iter.next().map(Atom::high_z_to_undefined).unwrap();

        let (high_state, low_state) = next.state.widening_shr(self.bit_shift);
        let (high_valid, low_valid) = next.valid.widening_shr(self.bit_shift);

        self.current = Atom {
            state: high_state,
            valid: high_valid,
        };

        Some(Atom {
            state: current.state | low_state,
            valid: current.valid | low_valid,
        })
    }
}

pub(super) fn lshr(
    width: NonZeroU8,
    shamnt_width: NonZeroU8,
    out: &mut [Atom],
    val: &[Atom],
    shamnt: Atom,
) -> OpResult {
    perform_shift(width, shamnt_width, out, val, shamnt, ShrIter::new_logical)
}

pub(super) fn ashr(
    width: NonZeroU8,
    shamnt_width: NonZeroU8,
    out: &mut [Atom],
    val: &[Atom],
    shamnt: Atom,
) -> OpResult {
    perform_shift(
        width,
        shamnt_width,
        out,
        val,
        shamnt,
        ShrIter::new_arithmetic,
    )
}

struct SliceShiftIter<'a> {
    iter: std::iter::Skip<std::slice::Iter<'a, Atom>>,
    bit_shift: AtomOffset,
    current: Atom,
}

impl<'a> SliceShiftIter<'a> {
    #[inline]
    fn new(val: &'a [Atom], shamnt: usize) -> Self {
        let atom_shift = shamnt / (Atom::BITS.get() as usize);
        let bit_shift = unsafe {
            // SAFETY: <anything> % 32 = [0..31]
            AtomOffset::new_unchecked((shamnt % (Atom::BITS.get() as usize)) as u8)
        };

        let mut iter = val.iter().skip(atom_shift);
        let current = iter.next().copied().unwrap_or(Atom::UNDEFINED);
        let current = Atom {
            state: current.state >> bit_shift,
            valid: current.valid >> bit_shift,
        };

        Self {
            iter,
            bit_shift,
            current,
        }
    }
}

impl Iterator for SliceShiftIter<'_> {
    type Item = Atom;

    #[inline]
    fn next(&mut self) -> Option<Self::Item> {
        let current = self.current;
        let next = self.iter.next().copied().unwrap_or(Atom::UNDEFINED);

        let (high_state, low_state) = next.state.widening_shr(self.bit_shift);
        let (high_valid, low_valid) = next.valid.widening_shr(self.bit_shift);

        self.current = Atom {
            state: high_state,
            valid: high_valid,
        };

        Some(Atom {
            state: current.state | low_state,
            valid: current.valid | low_valid,
        })
    }
}

pub(super) fn slice(width: NonZeroU8, out: &mut [Atom], val: &[Atom], offset: u8) -> OpResult {
    debug_assert_eq!(out.len(), width.safe_div_ceil(Atom::BITS).get() as usize);
    debug_assert!(out.len() <= val.len());

    let mut result = OpResult::Unchanged;

    let mut i = 0;
    let mut total_width = width.get();
    let mut val_iter = SliceShiftIter::new(val, offset as usize);
    while total_width >= Atom::BITS.get() {
        let out = get_mut!(out, i);
        let val = val_iter.next().unwrap();

        if !out.eq(val, AtomWidth::MAX) {
            result = OpResult::Changed;
        }
        *out = val;

        i += 1;
        total_width -= Atom::BITS.get();
    }

    if total_width > 0 {
        let last_out = get_mut!(out, i);
        let last_val = val_iter.next().unwrap();

        let last_width = unsafe {
            // SAFETY: the loop and if condition ensure that 0 < total_width < Atom::BITS
            AtomWidth::new_unchecked(total_width)
        };

        if !last_out.eq(last_val, last_width) {
            result = OpResult::Changed;
        }
        *last_out = last_val;
    }

    result
}

struct MergeShiftIter<'a> {
    iter: MaskingIter<std::iter::Copied<std::slice::Iter<'a, Atom>>>,
    atom_shift: usize,
    bit_shift: AtomOffset,
    carry: Atom,
}

impl<'a> MergeShiftIter<'a> {
    #[inline]
    fn new(width: NonZeroU8, val: &'a [Atom], shamnt: usize) -> Self {
        let atom_shift = shamnt / (Atom::BITS.get() as usize);
        let bit_shift = unsafe {
            // SAFETY: <anything> % 32 = [0..31]
            AtomOffset::new_unchecked((shamnt % (Atom::BITS.get() as usize)) as u8)
        };

        Self {
            iter: MaskingIter::new(width, Atom::HIGH_Z, val.iter().copied()),
            atom_shift,
            bit_shift,
            carry: Atom::HIGH_Z,
        }
    }
}

impl Iterator for MergeShiftIter<'_> {
    type Item = Atom;

    #[inline]
    fn next(&mut self) -> Option<Self::Item> {
        if self.atom_shift > 0 {
            self.atom_shift -= 1;
            Some(Atom::HIGH_Z)
        } else {
            let next = self.iter.next().unwrap();
            let (low_state, high_state) = next.state.widening_shl(self.bit_shift);
            let (low_valid, high_valid) = next.valid.widening_shl(self.bit_shift);
            let carry = self.carry;

            self.carry = Atom {
                state: high_state,
                valid: high_valid,
            };

            Some(Atom {
                state: low_state | carry.state,
                valid: low_valid | carry.valid,
            })
        }
    }
}

pub(super) fn merge_one(dst: &mut [Atom], src_width: NonZeroU8, src: &[Atom], shamnt: usize) {
    debug_assert_eq!(
        src.len(),
        src_width.safe_div_ceil(Atom::BITS).get() as usize
    );
    debug_assert!(dst.len() >= src.len());

    let src_iter = MergeShiftIter::new(src_width, src, shamnt);
    for (dst, src) in izip!(dst, src_iter) {
        dst.state |= src.state;
        dst.valid |= src.valid;
    }
}

pub(super) fn copy(width: NonZeroU8, dst: &mut [Atom], src: &[Atom]) -> OpResult {
    debug_assert_eq!(src.len(), width.safe_div_ceil(Atom::BITS).get() as usize);
    debug_assert_eq!(dst.len(), src.len());

    let mut result = OpResult::Unchanged;
    let mut i = 0;
    let mut total_width = width.get();
    while total_width >= Atom::BITS.get() {
        let dst = get_mut!(dst, i);
        let src = get!(src, i);

        if !dst.eq(src, AtomWidth::MAX) {
            result = OpResult::Changed;
        }
        *dst = src;

        i += 1;
        total_width -= Atom::BITS.get();
    }

    if total_width > 0 {
        let dst = get_mut!(dst, i);
        let src = get!(src, i);

        let last_width = unsafe {
            // SAFETY: the loop and if condition ensure that 0 < total_width < Atom::BITS
            AtomWidth::new_unchecked(total_width)
        };

        if !dst.eq(src, last_width) {
            result = OpResult::Changed;
        }
        *dst = src;
    }

    result
}

#[inline]
fn reduce_atom<Op>(mut val: Atom, mut op: Op) -> Atom
where
    Op: FnMut(Atom, Atom) -> Atom,
{
    const O16: AtomOffset = unsafe { AtomOffset::new_unchecked(16) };
    const O8: AtomOffset = unsafe { AtomOffset::new_unchecked(8) };
    const O4: AtomOffset = unsafe { AtomOffset::new_unchecked(4) };
    const O2: AtomOffset = unsafe { AtomOffset::new_unchecked(2) };
    const O1: AtomOffset = unsafe { AtomOffset::new_unchecked(1) };

    let sh16 = Atom {
        state: val.state >> O16,
        valid: val.valid >> O16,
    };
    val = op(val, sh16);

    let sh8 = Atom {
        state: val.state >> O8,
        valid: val.valid >> O8,
    };
    val = op(val, sh8);

    let sh4 = Atom {
        state: val.state >> O4,
        valid: val.valid >> O4,
    };
    val = op(val, sh4);

    let sh2 = Atom {
        state: val.state >> O2,
        valid: val.valid >> O2,
    };
    val = op(val, sh2);

    let sh1 = Atom {
        state: val.state >> O1,
        valid: val.valid >> O1,
    };
    val = op(val, sh1);

    val
}

// TODO:
//   Maybe the horizontal operations can be implemented more efficiently using popcount.
//   This needs further investigation as it is unclear how to handle the Z and X states.

#[inline]
pub(super) fn horizontal_logic_and_impl(width: NonZeroU8, val: &[Atom]) -> Atom {
    let mut new = Atom::LOGIC_1;

    let mut total_width = width.get();
    for &(mut val) in val {
        let width = AtomWidth::new(total_width).unwrap_or(AtomWidth::MAX);
        total_width -= width.get();

        if width < AtomWidth::MAX {
            // set bits outside the width to Logic1
            let mask = LogicStorage::mask(width);
            val.state |= !mask;
            val.valid |= !mask;
        }

        new = logic_and_impl(new, val);
    }

    reduce_atom(new, logic_and_impl)
}

#[inline]
pub(super) fn horizontal_logic_or_impl(width: NonZeroU8, val: &[Atom]) -> Atom {
    let mut new = Atom::LOGIC_0;

    let mut total_width = width.get();
    for &(mut val) in val {
        let width = AtomWidth::new(total_width).unwrap_or(AtomWidth::MAX);
        total_width -= width.get();

        if width < AtomWidth::MAX {
            // set bits outside the width to Logic0
            let mask = LogicStorage::mask(width);
            val.state &= mask;
            val.valid |= !mask;
        }

        new = logic_or_impl(new, val);
    }

    reduce_atom(new, logic_or_impl)
}

pub(super) fn horizontal_logic_xor_impl(width: NonZeroU8, val: &[Atom]) -> Atom {
    let mut new = Atom::LOGIC_0;

    let mut total_width = width.get();
    for &(mut val) in val {
        let width = AtomWidth::new(total_width).unwrap_or(AtomWidth::MAX);
        total_width -= width.get();

        if width < AtomWidth::MAX {
            // set bits outside the width to Logic0
            let mask = LogicStorage::mask(width);
            val.state &= mask;
            val.valid |= !mask;
        }

        new = logic_xor_impl(new, val);
    }

    reduce_atom(new, logic_xor_impl)
}

pub(super) fn horizontal_logic_and(width: NonZeroU8, out: &mut Atom, val: &[Atom]) -> OpResult {
    let new = horizontal_logic_and_impl(width, val);

    if !out.eq(new, AtomWidth::MIN) {
        *out = new;
        OpResult::Changed
    } else {
        OpResult::Unchanged
    }
}

pub(super) fn horizontal_logic_or(width: NonZeroU8, out: &mut Atom, val: &[Atom]) -> OpResult {
    let new = horizontal_logic_or_impl(width, val);

    if !out.eq(new, AtomWidth::MIN) {
        *out = new;
        OpResult::Changed
    } else {
        OpResult::Unchanged
    }
}

pub(super) fn horizontal_logic_xor(width: NonZeroU8, out: &mut Atom, val: &[Atom]) -> OpResult {
    let new = horizontal_logic_xor_impl(width, val);

    if !out.eq(new, AtomWidth::MIN) {
        *out = new;
        OpResult::Changed
    } else {
        OpResult::Unchanged
    }
}

pub(super) fn horizontal_logic_nand(width: NonZeroU8, out: &mut Atom, val: &[Atom]) -> OpResult {
    let new = horizontal_logic_and_impl(width, val);
    let new = logic_not_impl(new);

    if !out.eq(new, AtomWidth::MIN) {
        *out = new;
        OpResult::Changed
    } else {
        OpResult::Unchanged
    }
}

pub(super) fn horizontal_logic_nor(width: NonZeroU8, out: &mut Atom, val: &[Atom]) -> OpResult {
    let new = horizontal_logic_or_impl(width, val);
    let new = logic_not_impl(new);

    if !out.eq(new, AtomWidth::MIN) {
        *out = new;
        OpResult::Changed
    } else {
        OpResult::Unchanged
    }
}

pub(super) fn horizontal_logic_xnor(width: NonZeroU8, out: &mut Atom, val: &[Atom]) -> OpResult {
    let new = horizontal_logic_xor_impl(width, val);
    let new = logic_not_impl(new);

    if !out.eq(new, AtomWidth::MIN) {
        *out = new;
        OpResult::Changed
    } else {
        OpResult::Unchanged
    }
}

pub(super) fn equal(width: NonZeroU8, out: &mut Atom, lhs: &[Atom], rhs: &[Atom]) -> OpResult {
    let mut new = Atom::LOGIC_1;

    let mut total_width = width.get();
    for (&lhs, &rhs) in izip!(lhs, rhs) {
        let width = AtomWidth::new(total_width).unwrap_or(AtomWidth::MAX);
        total_width -= width.get();

        if !lhs.is_valid(width) || !rhs.is_valid(width) {
            new = Atom::UNDEFINED;
            break;
        }

        if !lhs.eq(rhs, width) {
            new = Atom::LOGIC_0;
        }
    }

    if !out.eq(new, AtomWidth::MIN) {
        *out = new;
        OpResult::Changed
    } else {
        OpResult::Unchanged
    }
}

pub(super) fn not_equal(width: NonZeroU8, out: &mut Atom, lhs: &[Atom], rhs: &[Atom]) -> OpResult {
    let mut new = Atom::LOGIC_0;

    let mut total_width = width.get();
    for (&lhs, &rhs) in izip!(lhs, rhs) {
        let width = AtomWidth::new(total_width).unwrap_or(AtomWidth::MAX);
        total_width -= width.get();

        if !lhs.is_valid(width) || !rhs.is_valid(width) {
            new = Atom::UNDEFINED;
            break;
        }

        if !lhs.eq(rhs, width) {
            new = Atom::LOGIC_1;
        }
    }

    if !out.eq(new, AtomWidth::MIN) {
        *out = new;
        OpResult::Changed
    } else {
        OpResult::Unchanged
    }
}

#[inline]
fn cmp<Cmp>(width: NonZeroU8, out: &mut Atom, lhs: &[Atom], rhs: &[Atom], inv_cmp: Cmp) -> OpResult
where
    Cmp: Fn(LogicStorage, LogicStorage) -> bool,
{
    let mut new = Atom::LOGIC_1;

    'valid: {
        let mut iter = izip!(lhs, rhs).rev();

        let head_width = AtomWidth::new(width.get() % Atom::BITS.get()).unwrap_or(AtomWidth::MAX);
        if let Some((&lhs, &rhs)) = iter.next() {
            if !lhs.is_valid(head_width) || !rhs.is_valid(head_width) {
                new = Atom::UNDEFINED;
                break 'valid;
            }

            let mask = LogicStorage::mask(head_width);
            if inv_cmp(lhs.state & mask, rhs.state & mask) {
                new = Atom::LOGIC_0;
            }
        }

        for (&lhs, &rhs) in iter {
            if !lhs.is_valid(AtomWidth::MAX) || !rhs.is_valid(AtomWidth::MAX) {
                new = Atom::UNDEFINED;
                break 'valid;
            }

            if inv_cmp(lhs.state, rhs.state) {
                new = Atom::LOGIC_0;
            }
        }
    }

    if !out.eq(new, AtomWidth::MIN) {
        *out = new;
        OpResult::Changed
    } else {
        OpResult::Unchanged
    }
}

pub(super) fn less_than(width: NonZeroU8, out: &mut Atom, lhs: &[Atom], rhs: &[Atom]) -> OpResult {
    cmp(width, out, lhs, rhs, |a, b| a >= b)
}

pub(super) fn greater_than(
    width: NonZeroU8,
    out: &mut Atom,
    lhs: &[Atom],
    rhs: &[Atom],
) -> OpResult {
    cmp(width, out, lhs, rhs, |a, b| a <= b)
}

pub(super) fn less_than_or_equal(
    width: NonZeroU8,
    out: &mut Atom,
    lhs: &[Atom],
    rhs: &[Atom],
) -> OpResult {
    cmp(width, out, lhs, rhs, |a, b| a > b)
}

pub(super) fn greater_than_or_equal(
    width: NonZeroU8,
    out: &mut Atom,
    lhs: &[Atom],
    rhs: &[Atom],
) -> OpResult {
    cmp(width, out, lhs, rhs, |a, b| a < b)
}

#[inline]
fn cmp_signed<Cmp>(
    width: NonZeroU8,
    out: &mut Atom,
    lhs: &[Atom],
    rhs: &[Atom],
    inv_cmp: Cmp,
) -> OpResult
where
    Cmp: Fn(LogicStorage, LogicStorage, AtomWidth) -> bool,
{
    let mut new = Atom::LOGIC_1;

    'valid: {
        let mut iter = izip!(lhs, rhs).rev();

        let head_width = AtomWidth::new(width.get() % Atom::BITS.get()).unwrap_or(AtomWidth::MAX);
        if let Some((&lhs, &rhs)) = iter.next() {
            if !lhs.is_valid(head_width) || !rhs.is_valid(head_width) {
                new = Atom::UNDEFINED;
                break 'valid;
            }

            let mask = LogicStorage::mask(head_width);
            if inv_cmp(lhs.state & mask, rhs.state & mask, head_width) {
                new = Atom::LOGIC_0;
            }
        }

        for (&lhs, &rhs) in iter {
            if !lhs.is_valid(AtomWidth::MAX) || !rhs.is_valid(AtomWidth::MAX) {
                new = Atom::UNDEFINED;
                break 'valid;
            }

            if inv_cmp(lhs.state, rhs.state, AtomWidth::MAX) {
                new = Atom::LOGIC_0;
            }
        }
    }

    if !out.eq(new, AtomWidth::MIN) {
        *out = new;
        OpResult::Changed
    } else {
        OpResult::Unchanged
    }
}

pub(super) fn less_than_signed(
    width: NonZeroU8,
    out: &mut Atom,
    lhs: &[Atom],
    rhs: &[Atom],
) -> OpResult {
    cmp_signed(width, out, lhs, rhs, LogicStorage::ges)
}

pub(super) fn greater_than_signed(
    width: NonZeroU8,
    out: &mut Atom,
    lhs: &[Atom],
    rhs: &[Atom],
) -> OpResult {
    cmp_signed(width, out, lhs, rhs, LogicStorage::les)
}

pub(super) fn less_than_or_equal_signed(
    width: NonZeroU8,
    out: &mut Atom,
    lhs: &[Atom],
    rhs: &[Atom],
) -> OpResult {
    cmp_signed(width, out, lhs, rhs, LogicStorage::gts)
}

pub(super) fn greater_than_or_equal_signed(
    width: NonZeroU8,
    out: &mut Atom,
    lhs: &[Atom],
    rhs: &[Atom],
) -> OpResult {
    cmp_signed(width, out, lhs, rhs, LogicStorage::lts)
}

pub(super) fn zero_extend(
    val_width: NonZeroU8,
    out_width: NonZeroU8,
    val: &[Atom],
    out: &mut [Atom],
) -> OpResult {
    let val_tail_width =
        AtomWidth::new(val_width.get() % Atom::BITS.get()).unwrap_or(AtomWidth::MAX);
    let out_tail_width =
        AtomWidth::new(out_width.get() % Atom::BITS.get()).unwrap_or(AtomWidth::MAX);

    let mut val_iter = val.iter();
    let mut out_iter = out.iter_mut();

    let mut result = OpResult::Unchanged;

    while val_iter.len() > 1 {
        let val = *val_iter.next().unwrap();
        let out = out_iter.next().unwrap();

        if !out.eq(val, AtomWidth::MAX) {
            *out = val;
            result = OpResult::Changed;
        }
    }

    let val = *val_iter.next().unwrap();
    let out = out_iter.next().unwrap();

    let mask = LogicStorage::mask(val_tail_width);
    let extend = Atom::LOGIC_0;
    let val = Atom {
        state: (val.state & mask) | (extend.state & !mask),
        valid: (val.valid & mask) | (extend.valid & !mask),
    };

    let tail_width = if out_iter.len() == 0 {
        out_tail_width
    } else {
        AtomWidth::MAX
    };

    if !out.eq(val, tail_width) {
        *out = val;
        result = OpResult::Changed;
    }

    if out_iter.len() > 0 {
        while out_iter.len() > 1 {
            let out = out_iter.next().unwrap();

            if !out.eq(extend, AtomWidth::MAX) {
                *out = extend;
                result = OpResult::Changed;
            }
        }

        let out = out_iter.next().unwrap();

        if !out.eq(extend, out_tail_width) {
            *out = extend;
            result = OpResult::Changed;
        }
    }

    result
}

pub(super) fn sign_extend(
    val_width: NonZeroU8,
    out_width: NonZeroU8,
    val: &[Atom],
    out: &mut [Atom],
) -> OpResult {
    let val_tail_width =
        AtomWidth::new(val_width.get() % Atom::BITS.get()).unwrap_or(AtomWidth::MAX);
    let out_tail_width =
        AtomWidth::new(out_width.get() % Atom::BITS.get()).unwrap_or(AtomWidth::MAX);

    let mut val_iter = val.iter();
    let mut out_iter = out.iter_mut();

    let mut result = OpResult::Unchanged;

    while val_iter.len() > 1 {
        let val = *val_iter.next().unwrap();
        let out = out_iter.next().unwrap();

        if !out.eq(val, AtomWidth::MAX) {
            *out = val;
            result = OpResult::Changed;
        }
    }

    let val = *val_iter.next().unwrap();
    let out = out_iter.next().unwrap();

    let mask = LogicStorage::mask(val_tail_width);
    let extend = val
        .get_bit_state(AtomOffset::new(val_tail_width.get() - 1).unwrap())
        .splat();
    let val = Atom {
        state: (val.state & mask) | (extend.state & !mask),
        valid: (val.valid & mask) | (extend.valid & !mask),
    };

    let tail_width = if out_iter.len() == 0 {
        out_tail_width
    } else {
        AtomWidth::MAX
    };

    if !out.eq(val, tail_width) {
        *out = val;
        result = OpResult::Changed;
    }

    if out_iter.len() > 0 {
        while out_iter.len() > 1 {
            let out = out_iter.next().unwrap();

            if !out.eq(extend, AtomWidth::MAX) {
                *out = extend;
                result = OpResult::Changed;
            }
        }

        let out = out_iter.next().unwrap();

        if !out.eq(extend, out_tail_width) {
            *out = extend;
            result = OpResult::Changed;
        }
    }

    result
}