1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146

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),
            ))
        }
    }
}