1/*
2 * Copyright 2017-present Facebook, Inc.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17/**
18 * @author Giuseppe Ottaviano <ott@fb.com>
19 *
20 * Shared utils for BitVectorCoding.h and EliasFanoCoding.h.
21 */
22
23#pragma once
24
25#include <stddef.h>
26
27namespace folly {
28namespace compression {
29namespace detail {
30
31/**
32 * Helpers to store pointers to forward and skip pointer arrays only
33 * if they are used, that is, the quantum is nonzero. If it is 0, the
34 * class is empty, and the member is static to keep the syntax valid,
35 * thus it will take no space in a derived class thanks to empty base
36 * class optimization.
37 */
38template <size_t>
39class ForwardPointers {
40 protected:
41 explicit ForwardPointers(const unsigned char* ptr) : forwardPointers_(ptr) {}
42 const unsigned char* const forwardPointers_;
43};
44template <>
45class ForwardPointers<0> {
46 protected:
47 explicit ForwardPointers(const unsigned char*) {}
48 constexpr static const unsigned char* const forwardPointers_{};
49};
50
51template <size_t>
52class SkipPointers {
53 protected:
54 explicit SkipPointers(const unsigned char* ptr) : skipPointers_(ptr) {}
55 const unsigned char* const skipPointers_;
56};
57template <>
58class SkipPointers<0> {
59 protected:
60 explicit SkipPointers(const unsigned char*) {}
61 constexpr static const unsigned char* const skipPointers_{};
62};
63} // namespace detail
64} // namespace compression
65} // namespace folly
66