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
|
// Copyright 2021 The Abseil Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "absl/strings/internal/cord_rep_btree_navigator.h"
#include <cassert>
#include "absl/strings/internal/cord_internal.h"
#include "absl/strings/internal/cord_rep_btree.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace cord_internal {
using ReadResult = CordRepBtreeNavigator::ReadResult;
namespace {
// Returns a `CordRepSubstring` from `rep` starting at `offset` of size `n`.
// If `rep` is already a `CordRepSubstring` instance, an adjusted instance is
// created based on the old offset and new offset.
// Adopts a reference on `rep`. Rep must be a valid data edge. Returns
// nullptr if `n == 0`, `rep` if `n == rep->length`.
// Requires `offset < rep->length` and `offset + n <= rep->length`.
// TODO(192061034): move to utility library in internal and optimize for small
// substrings of larger reps.
inline CordRep* Substring(CordRep* rep, size_t offset, size_t n) {
assert(n <= rep->length);
assert(offset < rep->length);
assert(offset <= rep->length - n);
assert(CordRepBtree::IsDataEdge(rep));
if (n == 0) return nullptr;
if (n == rep->length) return CordRep::Ref(rep);
if (rep->tag == SUBSTRING) {
offset += rep->substring()->start;
rep = rep->substring()->child;
}
CordRepSubstring* substring = new CordRepSubstring();
substring->length = n;
substring->tag = SUBSTRING;
substring->start = offset;
substring->child = CordRep::Ref(rep);
return substring;
}
inline CordRep* Substring(CordRep* rep, size_t offset) {
return Substring(rep, offset, rep->length - offset);
}
} // namespace
CordRepBtreeNavigator::Position CordRepBtreeNavigator::Skip(size_t n) {
int height = 0;
size_t index = index_[0];
CordRepBtree* node = node_[0];
CordRep* edge = node->Edge(index);
// Overall logic: Find an edge of at least the length we need to skip.
// We consume all edges which are smaller (i.e., must be 100% skipped).
// If we exhausted all edges on the current level, we move one level
// up the tree, and repeat until we either find the edge, or until we hit
// the top of the tree meaning the skip exceeds tree->length.
while (n >= edge->length) {
n -= edge->length;
while (++index == node->end()) {
if (++height > height_) return {nullptr, n};
node = node_[height];
index = index_[height];
}
edge = node->Edge(index);
}
// If we moved up the tree, descend down to the leaf level, consuming all
// edges that must be skipped.
while (height > 0) {
node = edge->btree();
index_[height] = index;
node_[--height] = node;
index = node->begin();
edge = node->Edge(index);
while (n >= edge->length) {
n -= edge->length;
++index;
assert(index != node->end());
edge = node->Edge(index);
}
}
index_[0] = index;
return {edge, n};
}
ReadResult CordRepBtreeNavigator::Read(size_t edge_offset, size_t n) {
int height = 0;
size_t length = edge_offset + n;
size_t index = index_[0];
CordRepBtree* node = node_[0];
CordRep* edge = node->Edge(index);
assert(edge_offset < edge->length);
if (length < edge->length) {
return {Substring(edge, edge_offset, n), length};
}
// Similar to 'Skip', we consume all edges that are inside the 'length' of
// data that needs to be read. If we exhaust the current level, we move one
// level up the tree and repeat until we hit the final edge that must be
// (partially) read. We consume all edges into `subtree`.
CordRepBtree* subtree = CordRepBtree::New(Substring(edge, edge_offset));
size_t subtree_end = 1;
do {
length -= edge->length;
while (++index == node->end()) {
index_[height] = index;
if (++height > height_) {
subtree->set_end(subtree_end);
if (length == 0) return {subtree, 0};
CordRep::Unref(subtree);
return {nullptr, length};
}
if (length != 0) {
subtree->set_end(subtree_end);
subtree = CordRepBtree::New(subtree);
subtree_end = 1;
}
node = node_[height];
index = index_[height];
}
edge = node->Edge(index);
if (length >= edge->length) {
subtree->length += edge->length;
subtree->edges_[subtree_end++] = CordRep::Ref(edge);
}
} while (length >= edge->length);
CordRepBtree* tree = subtree;
subtree->length += length;
// If we moved up the tree, descend down to the leaf level, consuming all
// edges that must be read, adding 'down' nodes to `subtree`.
while (height > 0) {
node = edge->btree();
index_[height] = index;
node_[--height] = node;
index = node->begin();
edge = node->Edge(index);
if (length != 0) {
CordRepBtree* right = CordRepBtree::New(height);
right->length = length;
subtree->edges_[subtree_end++] = right;
subtree->set_end(subtree_end);
subtree = right;
subtree_end = 0;
while (length >= edge->length) {
subtree->edges_[subtree_end++] = CordRep::Ref(edge);
length -= edge->length;
edge = node->Edge(++index);
}
}
}
// Add any (partial) edge still remaining at the leaf level.
if (length != 0) {
subtree->edges_[subtree_end++] = Substring(edge, 0, length);
}
subtree->set_end(subtree_end);
index_[0] = index;
return {tree, length};
}
} // namespace cord_internal
ABSL_NAMESPACE_END
} // namespace absl
|
