1/*
2 * Copyright (C) 2012 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 MINIKIN_SPARSE_BIT_SET_H
18#define MINIKIN_SPARSE_BIT_SET_H
19
20#include <stdint.h>
21#include <sys/types.h>
22#include <UniquePtr.h>
23
24// ---------------------------------------------------------------------------
25
26namespace android {
27
28// This is an implementation of a set of integers. It is optimized for
29// values that are somewhat sparse, in the ballpark of a maximum value
30// of thousands to millions. It is particularly efficient when there are
31// large gaps. The motivating example is Unicode coverage of a font, but
32// the abstraction itself is fully general.
33
34class SparseBitSet {
35public:
36    SparseBitSet(): mMaxVal(0) {
37    }
38
39    // Clear the set
40    void clear();
41
42    // Initialize the set to a new value, represented by ranges. For
43    // simplicity, these ranges are arranged as pairs of values,
44    // inclusive of start, exclusive of end, laid out in a uint32 array.
45    void initFromRanges(const uint32_t* ranges, size_t nRanges);
46
47    // Determine whether the value is included in the set
48    bool get(uint32_t ch) const {
49        if (ch >= mMaxVal) return false;
50        uint32_t *bitmap = &mBitmaps[mIndices[ch >> kLogValuesPerPage]];
51        uint32_t index = ch & kPageMask;
52        return (bitmap[index >> kLogBitsPerEl] & (kElFirst >> (index & kElMask))) != 0;
53    }
54
55    // One more than the maximum value in the set, or zero if empty
56    uint32_t length() const {
57        return mMaxVal;
58    }
59
60    // The next set bit starting at fromIndex, inclusive, or kNotFound
61    // if none exists.
62    uint32_t nextSetBit(uint32_t fromIndex) const;
63
64    static const uint32_t kNotFound = ~0u;
65
66private:
67    static const int kLogValuesPerPage = 8;
68    static const int kPageMask = (1 << kLogValuesPerPage) - 1;
69    static const int kLogBytesPerEl = 2;
70    static const int kLogBitsPerEl = kLogBytesPerEl + 3;
71    static const int kElMask = (1 << kLogBitsPerEl) - 1;
72    // invariant: sizeof(element) == (1 << kLogBytesPerEl)
73    typedef uint32_t element;
74    static const element kElAllOnes = ~((element)0);
75    static const element kElFirst = ((element)1) << kElMask;
76    static const uint32_t noZeroPage = ~0u;
77
78    static uint32_t calcNumPages(const uint32_t* ranges, size_t nRanges);
79    static int CountLeadingZeros(element x);
80
81    uint32_t mMaxVal;
82    UniquePtr<uint32_t[]> mIndices;
83    UniquePtr<element[]> mBitmaps;
84    uint32_t mZeroPageIndex;
85};
86
87// Note: this thing cannot be used in vectors yet. If that were important, we'd need to
88// make the copy constructor work, and probably set up move traits as well.
89
90}; // namespace android
91
92#endif // MINIKIN_SPARSE_BIT_SET_H
93