forked from apache/arrow-rs
-
Notifications
You must be signed in to change notification settings - Fork 0
/
bit_iterator.rs
202 lines (177 loc) · 6.62 KB
/
bit_iterator.rs
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
// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements. See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership. The ASF licenses this file
// to you 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
//
// http://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.
use arrow_buffer::bit_chunk_iterator::{UnalignedBitChunk, UnalignedBitChunkIterator};
use std::result::Result;
/// Iterator of contiguous ranges of set bits within a provided packed bitmask
///
/// Returns `(usize, usize)` each representing an interval where the corresponding
/// bits in the provides mask are set
///
#[derive(Debug)]
pub struct BitSliceIterator<'a> {
iter: UnalignedBitChunkIterator<'a>,
len: usize,
current_offset: i64,
current_chunk: u64,
}
impl<'a> BitSliceIterator<'a> {
/// Create a new [`BitSliceIterator`] from the provide `buffer`,
/// and `offset` and `len` in bits
pub fn new(buffer: &'a [u8], offset: usize, len: usize) -> Self {
let chunk = UnalignedBitChunk::new(buffer, offset, len);
let mut iter = chunk.iter();
let current_offset = -(chunk.lead_padding() as i64);
let current_chunk = iter.next().unwrap_or(0);
Self {
iter,
len,
current_offset,
current_chunk,
}
}
/// Returns `Some((chunk_offset, bit_offset))` for the next chunk that has at
/// least one bit set, or None if there is no such chunk.
///
/// Where `chunk_offset` is the bit offset to the current `u64` chunk
/// and `bit_offset` is the offset of the first `1` bit in that chunk
fn advance_to_set_bit(&mut self) -> Option<(i64, u32)> {
loop {
if self.current_chunk != 0 {
// Find the index of the first 1
let bit_pos = self.current_chunk.trailing_zeros();
return Some((self.current_offset, bit_pos));
}
self.current_chunk = self.iter.next()?;
self.current_offset += 64;
}
}
}
impl<'a> Iterator for BitSliceIterator<'a> {
type Item = (usize, usize);
fn next(&mut self) -> Option<Self::Item> {
// Used as termination condition
if self.len == 0 {
return None;
}
let (start_chunk, start_bit) = self.advance_to_set_bit()?;
// Set bits up to start
self.current_chunk |= (1 << start_bit) - 1;
loop {
if self.current_chunk != u64::MAX {
// Find the index of the first 0
let end_bit = self.current_chunk.trailing_ones();
// Zero out up to end_bit
self.current_chunk &= !((1 << end_bit) - 1);
return Some((
(start_chunk + start_bit as i64) as usize,
(self.current_offset + end_bit as i64) as usize,
));
}
match self.iter.next() {
Some(next) => {
self.current_chunk = next;
self.current_offset += 64;
}
None => {
return Some((
(start_chunk + start_bit as i64) as usize,
std::mem::replace(&mut self.len, 0),
));
}
}
}
}
}
/// An iterator of `usize` whose index in a provided bitmask is true
///
/// This provides the best performance on most masks, apart from those which contain
/// large runs and therefore favour [`BitSliceIterator`]
#[derive(Debug)]
pub struct BitIndexIterator<'a> {
current_chunk: u64,
chunk_offset: i64,
iter: UnalignedBitChunkIterator<'a>,
}
impl<'a> BitIndexIterator<'a> {
/// Create a new [`BitIndexIterator`] from the provide `buffer`,
/// and `offset` and `len` in bits
pub fn new(buffer: &'a [u8], offset: usize, len: usize) -> Self {
let chunks = UnalignedBitChunk::new(buffer, offset, len);
let mut iter = chunks.iter();
let current_chunk = iter.next().unwrap_or(0);
let chunk_offset = -(chunks.lead_padding() as i64);
Self {
current_chunk,
chunk_offset,
iter,
}
}
}
impl<'a> Iterator for BitIndexIterator<'a> {
type Item = usize;
fn next(&mut self) -> Option<Self::Item> {
loop {
if self.current_chunk != 0 {
let bit_pos = self.current_chunk.trailing_zeros();
self.current_chunk ^= 1 << bit_pos;
return Some((self.chunk_offset + bit_pos as i64) as usize);
}
self.current_chunk = self.iter.next()?;
self.chunk_offset += 64;
}
}
}
/// Calls the provided closure for each index in the provided null mask that is set,
/// using an adaptive strategy based on the null count
///
/// Ideally this would be encapsulated in an [`Iterator`] that would determine the optimal
/// strategy up front, and then yield indexes based on this.
///
/// Unfortunately, external iteration based on the resulting [`Iterator`] would match the strategy
/// variant on each call to [`Iterator::next`], and LLVM generally cannot eliminate this.
///
/// One solution to this might be internal iteration, e.g. [`Iterator::try_fold`], however,
/// it is currently [not possible] to override this for custom iterators in stable Rust.
///
/// As such this is the next best option
///
/// [not possible]: https://github.com/rust-lang/rust/issues/69595
#[inline]
pub fn try_for_each_valid_idx<E, F: FnMut(usize) -> Result<(), E>>(
len: usize,
offset: usize,
null_count: usize,
nulls: Option<&[u8]>,
f: F,
) -> Result<(), E> {
let valid_count = len - null_count;
if valid_count == len {
(0..len).try_for_each(f)
} else if null_count != len {
let selectivity = valid_count as f64 / len as f64;
if selectivity > 0.8 {
BitSliceIterator::new(nulls.unwrap(), offset, len)
.flat_map(|(start, end)| start..end)
.try_for_each(f)
} else {
BitIndexIterator::new(nulls.unwrap(), offset, len).try_for_each(f)
}
} else {
Ok(())
}
}
// Note: tests located in filter module