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 : public std::iterator<std::forward_iterator_tag, uint32_t, ptrdiff_t, void, void> {
37 static_assert(std::is_integral<T>::value, "T must be integral");
38 static_assert(std::is_unsigned<T>::value, "T must be unsigned");
39
40 static_assert(sizeof(T) == sizeof(uint32_t) || sizeof(T) == sizeof(uint64_t), "Unsupported size");
41
42 public:
BitIteratorBase()43 BitIteratorBase() : bits_(0u) { }
BitIteratorBase(T bits)44 explicit BitIteratorBase(T bits) : bits_(bits) { }
45
46 Iter& operator++() {
47 DCHECK_NE(bits_, 0u);
48 uint32_t bit = *static_cast<Iter&>(*this);
49 bits_ &= ~(static_cast<T>(1u) << bit);
50 return static_cast<Iter&>(*this);
51 }
52
53 Iter& operator++(int) {
54 Iter tmp(static_cast<Iter&>(*this));
55 ++*this;
56 return tmp;
57 }
58
59 protected:
60 T bits_;
61
62 template <typename U, typename I>
63 friend bool operator==(const BitIteratorBase<U, I>& lhs, const BitIteratorBase<U, I>& rhs);
64 };
65
66 template <typename T, typename Iter>
67 bool operator==(const BitIteratorBase<T, Iter>& lhs, const BitIteratorBase<T, Iter>& rhs) {
68 return lhs.bits_ == rhs.bits_;
69 }
70
71 template <typename T, typename Iter>
72 bool operator!=(const BitIteratorBase<T, Iter>& lhs, const BitIteratorBase<T, Iter>& rhs) {
73 return !(lhs == rhs);
74 }
75
76 template <typename T>
77 class LowToHighBitIterator : public BitIteratorBase<T, LowToHighBitIterator<T>> {
78 public:
79 using BitIteratorBase<T, LowToHighBitIterator<T>>::BitIteratorBase;
80
81 uint32_t operator*() const {
82 DCHECK_NE(this->bits_, 0u);
83 return CTZ(this->bits_);
84 }
85 };
86
87 template <typename T>
88 class HighToLowBitIterator : public BitIteratorBase<T, HighToLowBitIterator<T>> {
89 public:
90 using BitIteratorBase<T, HighToLowBitIterator<T>>::BitIteratorBase;
91
92 uint32_t operator*() const {
93 DCHECK_NE(this->bits_, 0u);
94 static_assert(std::numeric_limits<T>::radix == 2, "Unexpected radix!");
95 return std::numeric_limits<T>::digits - 1u - CLZ(this->bits_);
96 }
97 };
98
99 template <typename T>
LowToHighBits(T bits)100 IterationRange<LowToHighBitIterator<T>> LowToHighBits(T bits) {
101 return IterationRange<LowToHighBitIterator<T>>(
102 LowToHighBitIterator<T>(bits), LowToHighBitIterator<T>());
103 }
104
105 template <typename T>
HighToLowBits(T bits)106 IterationRange<HighToLowBitIterator<T>> HighToLowBits(T bits) {
107 return IterationRange<HighToLowBitIterator<T>>(
108 HighToLowBitIterator<T>(bits), HighToLowBitIterator<T>());
109 }
110
111 } // namespace art
112
113 #endif // ART_LIBARTBASE_BASE_BIT_UTILS_ITERATOR_H_
114