mirror of
https://github.com/mozilla/gecko-dev.git
synced 2024-11-24 05:11:16 +00:00
265e672179
# ignore-this-changeset --HG-- extra : amend_source : 4d301d3b0b8711c4692392aa76088ba7fd7d1022
130 lines
3.5 KiB
C++
130 lines
3.5 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
|
|
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
|
|
/* This Source Code Form is subject to the terms of the Mozilla Public
|
|
* License, v. 2.0. If a copy of the MPL was not distributed with this
|
|
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
|
|
|
|
/**
|
|
* A class to generate unique IDs in the range [ - 2^31, 0 )
|
|
*/
|
|
|
|
#ifndef MOZILLA_A11Y_IDSet_h_
|
|
#define MOZILLA_A11Y_IDSet_h_
|
|
|
|
#include "mozilla/Attributes.h"
|
|
#include "mozilla/MathAlgorithms.h"
|
|
#include "mozilla/SplayTree.h"
|
|
|
|
namespace mozilla {
|
|
namespace a11y {
|
|
|
|
/**
|
|
* On windows an accessible's id must be a negative 32 bit integer. It is
|
|
* important to support recycling arbitrary IDs because accessibles can be
|
|
* created and destroyed at any time in the life of a page. IDSet provides 2
|
|
* operations: generate an ID in the range (0, mMaxId], and release an ID so
|
|
* it can be allocated again. Allocated ID are tracked by a sparse bitmap
|
|
* implemented with a splay tree. Nodes in the tree are keyed by the upper N
|
|
* bits of the ID, and the node contains a bitmap tracking the allocation of
|
|
* 2^(ceil(log2(mMaxId)) - N) IDs.
|
|
*
|
|
* Note that negation is handled by MsaaIdGenerator as it performs additional
|
|
* decoration on the ID generated by IDSet.
|
|
* @see mozilla::a11y::MsaaIdGenerator
|
|
*/
|
|
class IDSet {
|
|
public:
|
|
constexpr explicit IDSet(const uint32_t aMaxIdBits)
|
|
: mBitSet(),
|
|
mIdx(0),
|
|
mMaxId((1UL << aMaxIdBits) - 1UL),
|
|
mMaxIdx(mMaxId / bitsPerElt) {}
|
|
|
|
/**
|
|
* Return a new unique id.
|
|
*/
|
|
uint32_t GetID() {
|
|
uint32_t idx = mIdx;
|
|
while (true) {
|
|
BitSetElt* elt = mBitSet.findOrInsert(BitSetElt(idx));
|
|
if (elt->mBitvec[0] != UINT64_MAX) {
|
|
uint32_t i = CountTrailingZeroes64(~elt->mBitvec[0]);
|
|
|
|
elt->mBitvec[0] |= (1ull << i);
|
|
mIdx = idx;
|
|
return (elt->mIdx * bitsPerElt + i);
|
|
}
|
|
|
|
if (elt->mBitvec[1] != UINT64_MAX) {
|
|
uint32_t i = CountTrailingZeroes64(~elt->mBitvec[1]);
|
|
|
|
elt->mBitvec[1] |= (1ull << i);
|
|
mIdx = idx;
|
|
return (elt->mIdx * bitsPerElt + bitsPerWord + i);
|
|
}
|
|
|
|
idx++;
|
|
if (idx > mMaxIdx) {
|
|
idx = 0;
|
|
}
|
|
|
|
if (idx == mIdx) {
|
|
MOZ_CRASH("used up all the available ids");
|
|
}
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Free a no longer required id so it may be allocated again.
|
|
*/
|
|
void ReleaseID(uint32_t aID) {
|
|
MOZ_ASSERT(aID < mMaxId);
|
|
|
|
uint32_t idx = aID / bitsPerElt;
|
|
mIdx = idx;
|
|
BitSetElt* elt = mBitSet.find(BitSetElt(idx));
|
|
MOZ_ASSERT(elt);
|
|
|
|
uint32_t vecIdx = (aID % bitsPerElt) / bitsPerWord;
|
|
elt->mBitvec[vecIdx] &= ~(1ull << (aID % bitsPerWord));
|
|
if (elt->mBitvec[0] == 0 && elt->mBitvec[1] == 0) {
|
|
delete mBitSet.remove(*elt);
|
|
}
|
|
}
|
|
|
|
private:
|
|
static const unsigned int wordsPerElt = 2;
|
|
static const unsigned int bitsPerWord = 64;
|
|
static const unsigned int bitsPerElt = wordsPerElt * bitsPerWord;
|
|
|
|
struct BitSetElt : mozilla::SplayTreeNode<BitSetElt> {
|
|
explicit BitSetElt(uint32_t aIdx) : mIdx(aIdx) {
|
|
mBitvec[0] = mBitvec[1] = 0;
|
|
}
|
|
|
|
uint64_t mBitvec[wordsPerElt];
|
|
uint32_t mIdx;
|
|
|
|
static int compare(const BitSetElt& a, const BitSetElt& b) {
|
|
if (a.mIdx == b.mIdx) {
|
|
return 0;
|
|
}
|
|
|
|
if (a.mIdx < b.mIdx) {
|
|
return -1;
|
|
}
|
|
return 1;
|
|
}
|
|
};
|
|
|
|
SplayTree<BitSetElt, BitSetElt> mBitSet;
|
|
uint32_t mIdx;
|
|
const uint32_t mMaxId;
|
|
const uint32_t mMaxIdx;
|
|
};
|
|
|
|
} // namespace a11y
|
|
} // namespace mozilla
|
|
|
|
#endif
|