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    use super::bitmask::BitMask;
    use super::EMPTY;
    use core::mem;

    #[cfg(target_arch = "x86")]
    use core::arch::x86;
    #[cfg(target_arch = "x86_64")]
    use core::arch::x86_64 as x86;

    pub type BitMaskWord = u16;
    pub const BITMASK_STRIDE: usize = 1;
    pub const BITMASK_MASK: BitMaskWord = 0xffff;

    /// Abstraction over a group of control bytes which can be scanned in
    /// parallel.
    ///
    /// This implementation uses a 128-bit SSE value.
    #[derive(Copy, Clone)]
    pub struct Group(x86::__m128i);

    // FIXME: https://github.com/rust-lang/rust-clippy/issues/3859
    #[allow(clippy::use_self)]
    impl Group {
        /// Number of bytes in the group.
        pub const WIDTH: usize = mem::size_of::<Self>();

        /// Returns a full group of empty bytes, suitable for use as the initial
        /// value for an empty hash table.
        ///
        /// This is guaranteed to be aligned to the group size.
        #[inline]
        #[allow(clippy::items_after_statements)]
        pub const fn static_empty() -> &'static [u8; Group::WIDTH] {
            #[repr(C)]
            struct AlignedBytes {
                _align: [Group; 0],
                bytes: [u8; Group::WIDTH],
            }
            const ALIGNED_BYTES: AlignedBytes = AlignedBytes {
                _align: [],
                bytes: [EMPTY; Group::WIDTH],
            };
            &ALIGNED_BYTES.bytes
        }

        /// Loads a group of bytes starting at the given address.
        #[inline]
        #[allow(clippy::cast_ptr_alignment)] // unaligned load
        pub unsafe fn load(ptr: *const u8) -> Self {
            Group(x86::_mm_loadu_si128(ptr.cast()))
        }

        /// Loads a group of bytes starting at the given address, which must be
        /// aligned to `mem::align_of::<Group>()`.
        #[inline]
        #[allow(clippy::cast_ptr_alignment)]
        pub unsafe fn load_aligned(ptr: *const u8) -> Self {
            // FIXME: use align_offset once it stabilizes
            debug_assert_eq!(ptr as usize & (mem::align_of::<Self>() - 1), 0);
            Group(x86::_mm_load_si128(ptr.cast()))
        }

        /// Stores the group of bytes to the given address, which must be
        /// aligned to `mem::align_of::<Group>()`.
        #[inline]
        #[allow(clippy::cast_ptr_alignment)]
        pub unsafe fn store_aligned(self, ptr: *mut u8) {
            // FIXME: use align_offset once it stabilizes
            debug_assert_eq!(ptr as usize & (mem::align_of::<Self>() - 1), 0);
            x86::_mm_store_si128(ptr.cast(), self.0);
        }

        /// Returns a `BitMask` indicating all bytes in the group which have
        /// the given value.
        #[inline]
        pub fn match_byte(self, byte: u8) -> BitMask {
            #[allow(
                clippy::cast_possible_wrap, // byte: u8 as i8
                // byte: i32 as u16
                //   note: _mm_movemask_epi8 returns a 16-bit mask in a i32, the
                //   upper 16-bits of the i32 are zeroed:
                clippy::cast_sign_loss,
                clippy::cast_possible_truncation
            )]
            unsafe {
                let cmp = x86::_mm_cmpeq_epi8(self.0, x86::_mm_set1_epi8(byte as i8));
                BitMask(x86::_mm_movemask_epi8(cmp) as u16)
            }
        }

        /// Returns a `BitMask` indicating all bytes in the group which are
        /// `EMPTY`.
        #[inline]
        pub fn match_empty(self) -> BitMask {
            self.match_byte(EMPTY)
        }

        /// Returns a `BitMask` indicating all bytes in the group which are
        /// `EMPTY` or `DELETED`.
        #[inline]
        pub fn match_empty_or_deleted(self) -> BitMask {
            #[allow(
                // byte: i32 as u16
                //   note: _mm_movemask_epi8 returns a 16-bit mask in a i32, the
                //   upper 16-bits of the i32 are zeroed:
                clippy::cast_sign_loss,
                clippy::cast_possible_truncation
            )]
            unsafe {
                // A byte is EMPTY or DELETED iff the high bit is set
                BitMask(x86::_mm_movemask_epi8(self.0) as u16)
            }
        }

        /// Returns a `BitMask` indicating all bytes in the group which are full.
        #[inline]
        pub fn match_full(&self) -> BitMask {
            self.match_empty_or_deleted().invert()
        }

        /// Performs the following transformation on all bytes in the group:
        /// - `EMPTY => EMPTY`
        /// - `DELETED => EMPTY`
        /// - `FULL => DELETED`
        #[inline]
        pub fn convert_special_to_empty_and_full_to_deleted(self) -> Self {
            // Map high_bit = 1 (EMPTY or DELETED) to 1111_1111
            // and high_bit = 0 (FULL) to 1000_0000
            //
            // Here's this logic expanded to concrete values:
            //   let special = 0 > byte = 1111_1111 (true) or 0000_0000 (false)
            //   1111_1111 | 1000_0000 = 1111_1111
            //   0000_0000 | 1000_0000 = 1000_0000
            #[allow(
                clippy::cast_possible_wrap, // byte: 0x80_u8 as i8
            )]
            unsafe {
                let zero = x86::_mm_setzero_si128();
                let special = x86::_mm_cmpgt_epi8(zero, self.0);
                Group(x86::_mm_or_si128(
                    special,
                    x86::_mm_set1_epi8(0x80_u8 as i8),
                ))
            }
        }
    }