artful 0.1.1

Low-memory overhead and high-performance adaptive radix tree
Documentation 
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
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217

use crate::node::ArtNode;
use crate::node16::Node16;
use crate::ArtKey;
use crate::Header;

pub(crate) struct Node4<K: ArtKey, V, const MAX_PARTIAL_LEN: usize> {
    pub(crate) header: Header<MAX_PARTIAL_LEN>,
    pub(crate) key: [u8; 4],
    pub(crate) children: [ArtNode<K, V, MAX_PARTIAL_LEN>; 4],
    pub(crate) prefixed_child: ArtNode<K, V, MAX_PARTIAL_LEN>,
}

impl<K: ArtKey, V, const MAX_PARTIAL_LEN: usize> Default for Node4<K, V, MAX_PARTIAL_LEN> {
    fn default() -> Node4<K, V, MAX_PARTIAL_LEN> {
        Node4 {
            header: Default::default(),
            key: [0; 4],
            children: [
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
            ],
            prefixed_child: ArtNode::default(),
        }
    }
}

impl<K: ArtKey, V, const MAX_PARTIAL_LEN: usize> Node4<K, V, MAX_PARTIAL_LEN> {
    #[inline(always)]
    pub(crate) fn is_full(&self) -> bool {
        self.header.non_null_children == 4
    }

    #[inline(always)]
    pub(crate) fn minimum_child(&self) -> Option<&ArtNode<K, V, MAX_PARTIAL_LEN>> {
        if !self.prefixed_child.is_none() {
            Some(&self.prefixed_child)
        } else {
            Some(&self.children[0])
        }
    }

    #[inline]
    pub(crate) fn get_child(&self, key: (u8, bool)) -> Option<&ArtNode<K, V, MAX_PARTIAL_LEN>> {
        if !key.1 {
            return Some(&self.prefixed_child);
        }

        Some(&self.children[self.find_child_index(key.0)?])
    }

    pub(crate) fn get_mut_child(
        &mut self,
        key: (u8, bool),
    ) -> Option<&mut ArtNode<K, V, MAX_PARTIAL_LEN>> {
        if !key.1 {
            return Some(&mut self.prefixed_child);
        }

        Some(&mut self.children[self.find_child_index(key.0)?])
    }

    pub(crate) fn insert_child(
        &mut self,
        valid_key: (u8, bool),
        mut new_child: ArtNode<K, V, MAX_PARTIAL_LEN>,
    ) {
        if !valid_key.1 {
            assert!(self.prefixed_child.is_none());
            std::mem::swap(&mut self.prefixed_child, &mut new_child);
            return;
        }
        assert!(self.header.non_null_children < 4);

        let key_byte = valid_key.0;
        // find first index greater than or equal to key_byte
        let mut index = 0;
        while (index < self.header.non_null_children) && self.key[index as usize] < key_byte {
            index += 1;
        }

        if !self.children[index as usize].is_none() {
            let mut i = self.header.non_null_children;
            while i > index {
                let mut moved = std::mem::take(&mut self.children[i as usize - 1]);
                std::mem::swap(&mut self.children[i as usize], &mut moved);
                self.key[i as usize] = self.key[i as usize - 1];
                i -= 1;
            }
        }

        self.key[index as usize] = key_byte;
        std::mem::swap(&mut self.children[index as usize], &mut new_child);

        if !new_child.is_none() && !new_child.is_leaf() {
            assert_eq!(0, new_child.header().non_null_children);
        }

        self.header.non_null_children += 1;
    }

    #[inline(always)]
    pub(crate) fn grow(&mut self) -> Box<Node16<K, V, MAX_PARTIAL_LEN>> {
        assert_eq!(self.header.non_null_children, 4);
        let mut node16: Box<Node16<K, V, MAX_PARTIAL_LEN>> = Box::default();
        // copy invalid child
        std::mem::swap(&mut self.prefixed_child, &mut node16.prefixed_child);
        // copy child
        std::mem::swap(&mut self.children[0], &mut node16.children[0]);
        std::mem::swap(&mut self.children[1], &mut node16.children[1]);
        std::mem::swap(&mut self.children[2], &mut node16.children[2]);
        std::mem::swap(&mut self.children[3], &mut node16.children[3]);
        node16.key[0] = self.key[0];
        node16.key[1] = self.key[1];
        node16.key[2] = self.key[2];
        node16.key[3] = self.key[3];
        // copy the old node header to the new grown node.
        node16.header.partial.clone_from(&self.header.partial);
        node16.header.non_null_children = self.header.non_null_children;
        // node16.header = self.header;
        node16
    }

    pub fn is_few(&self) -> bool {
        let mut child_num = self.header.non_null_children;
        if !self.prefixed_child.is_none() {
            child_num += 1;
        }

        child_num < 2
    }

    pub(crate) fn remove_child(
        &mut self,
        valid_key: (u8, bool),
    ) -> Option<ArtNode<K, V, MAX_PARTIAL_LEN>> {
        if !valid_key.1 {
            assert_eq!(self.prefixed_child.is_none(), false);
            return Some(std::mem::take(&mut self.prefixed_child));
        }

        // TODO: This time the lookup can be optimized to be passed externally.
        let mut idx = self.find_child_index(valid_key.0)?;
        self.key[idx] = 0;
        self.header.non_null_children -= 1;
        let child = std::mem::take(&mut self.children[idx]);

        // to keep order
        while idx < self.header.non_null_children as usize {
            self.key[idx] = self.key[idx + 1];
            let mut moved = std::mem::take(&mut self.children[idx + 1]);
            std::mem::swap(&mut self.children[idx], &mut moved);
            idx += 1
        }

        // again remaining
        while idx < 4 {
            let _ = std::mem::take(&mut self.children[idx]);
            idx += 1
        }

        Some(child)
    }

    #[inline]
    fn find_child_index(&self, key: u8) -> Option<usize> {
        for i in 0..self.header.non_null_children {
            if self.key[i as usize] == key {
                return Some(i as usize);
            }
        }

        None
    }

    // shrink node4
    /// Safety: the node number of children must be equal 1 (include prefix child).
    pub(crate) fn shrink_to_fit(&mut self) -> ArtNode<K, V, MAX_PARTIAL_LEN> {
        let mut single_child = std::mem::take(&mut self.children[0]);
        if single_child.is_none() {
            assert_eq!(self.prefixed_child.is_none(), false);
            single_child = std::mem::take(&mut self.prefixed_child);
        }

        if single_child.is_leaf() {
            return single_child;
        }

        // shrink single child
        // 1. Merge the key pointing to a single child
        let mut prefix_len = self.header.partial.len as usize;
        if prefix_len < MAX_PARTIAL_LEN {
            self.header.partial.data[prefix_len] = self.key[0];
            prefix_len += 1;
        }

        // let header = single_child.header_mut();
        let mut header = Header::<MAX_PARTIAL_LEN>::default();
        header.partial.clone_from(&single_child.header().partial);
        header.non_null_children = single_child.header().non_null_children;

        // 2. Merge partial parts of the Child
        if prefix_len < MAX_PARTIAL_LEN {
            let minimum = std::cmp::min(header.partial.len as usize, MAX_PARTIAL_LEN - prefix_len);
            self.header.partial.data[prefix_len..prefix_len + minimum]
                .copy_from_slice(&header.partial.data[..minimum]);
            prefix_len += minimum;
        }

        let minimum = std::cmp::min(prefix_len, MAX_PARTIAL_LEN);
        header.partial.data[..minimum].copy_from_slice(&self.header.partial.data[..minimum]);
        header.partial.len += (self.header.partial.len + 1) as u32;
        std::mem::swap(single_child.header_mut(), &mut header);
        single_child
    }
}