1 /*
2 * Copyright (C) 2015 The Android Open Source Project
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 #ifndef ART_LIBARTBASE_BASE_BIT_UTILS_ITERATOR_H_
18 #define ART_LIBARTBASE_BASE_BIT_UTILS_ITERATOR_H_
19
20 #include <iterator>
21 #include <limits>
22 #include <type_traits>
23
24 #include <android-base/logging.h>
25
26 #include "bit_utils.h"
27 #include "iteration_range.h"
28 #include "stl_util.h"
29
30 namespace art {
31
32 // Using the Curiously Recurring Template Pattern to implement everything shared
33 // by LowToHighBitIterator and HighToLowBitIterator, i.e. everything but operator*().
34 template <typename T, typename Iter>
35 class BitIteratorBase {
36 static_assert(std::is_integral_v<T>, "T must be integral");
37 static_assert(std::is_unsigned_v<T>, "T must be unsigned");
38
39 static_assert(sizeof(T) == sizeof(uint32_t) || sizeof(T) == sizeof(uint64_t), "Unsupported size");
40
41 public:
42 using iterator_category = std::forward_iterator_tag;
43 using value_type = uint32_t;
44 using difference_type = ptrdiff_t;
45 using pointer = void;
46 using reference = void;
47
BitIteratorBase()48 BitIteratorBase() : bits_(0u) { }
BitIteratorBase(T bits)49 explicit BitIteratorBase(T bits) : bits_(bits) { }
50
51 Iter& operator++() {
52 DCHECK_NE(bits_, 0u);
53 uint32_t bit = *static_cast<Iter&>(*this);
54 bits_ &= ~(static_cast<T>(1u) << bit);
55 return static_cast<Iter&>(*this);
56 }
57
58 Iter& operator++(int) {
59 Iter tmp(static_cast<Iter&>(*this));
60 ++*this;
61 return tmp;
62 }
63
64 protected:
65 T bits_;
66
67 template <typename U, typename I>
68 friend bool operator==(const BitIteratorBase<U, I>& lhs, const BitIteratorBase<U, I>& rhs);
69 };
70
71 template <typename T, typename Iter>
72 bool operator==(const BitIteratorBase<T, Iter>& lhs, const BitIteratorBase<T, Iter>& rhs) {
73 return lhs.bits_ == rhs.bits_;
74 }
75
76 template <typename T, typename Iter>
77 bool operator!=(const BitIteratorBase<T, Iter>& lhs, const BitIteratorBase<T, Iter>& rhs) {
78 return !(lhs == rhs);
79 }
80
81 template <typename T>
82 class LowToHighBitIterator : public BitIteratorBase<T, LowToHighBitIterator<T>> {
83 public:
84 using BitIteratorBase<T, LowToHighBitIterator<T>>::BitIteratorBase;
85
86 uint32_t operator*() const {
87 DCHECK_NE(this->bits_, 0u);
88 return CTZ(this->bits_);
89 }
90 };
91
92 template <typename T>
93 class HighToLowBitIterator : public BitIteratorBase<T, HighToLowBitIterator<T>> {
94 public:
95 using BitIteratorBase<T, HighToLowBitIterator<T>>::BitIteratorBase;
96
97 uint32_t operator*() const {
98 DCHECK_NE(this->bits_, 0u);
99 static_assert(std::numeric_limits<T>::radix == 2, "Unexpected radix!");
100 return std::numeric_limits<T>::digits - 1u - CLZ(this->bits_);
101 }
102 };
103
104 template <typename T>
LowToHighBits(T bits)105 IterationRange<LowToHighBitIterator<T>> LowToHighBits(T bits) {
106 return IterationRange<LowToHighBitIterator<T>>(
107 LowToHighBitIterator<T>(bits), LowToHighBitIterator<T>());
108 }
109
110 template <typename T>
HighToLowBits(T bits)111 IterationRange<HighToLowBitIterator<T>> HighToLowBits(T bits) {
112 return IterationRange<HighToLowBitIterator<T>>(
113 HighToLowBitIterator<T>(bits), HighToLowBitIterator<T>());
114 }
115
116 } // namespace art
117
118 #endif // ART_LIBARTBASE_BASE_BIT_UTILS_ITERATOR_H_
119