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// Copyright 2023 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef UI_ACCESSIBILITY_AX_BIT_MAP_H_
#define UI_ACCESSIBILITY_AX_BIT_MAP_H_
#include "base/check.h"
#include "third_party/abseil-cpp/absl/types/optional.h"
#include <memory>
#include <string>
#include <tuple>
namespace ui {
// A helper class to store AX-related boolean enums.
template <typename T>
class AXBitMap {
public:
static const size_t kElementsPerMapBucket = 64;
AXBitMap() {
for (size_t i = 0;
i <= static_cast<size_t>(T::kMaxValue) / kElementsPerMapBucket; ++i) {
true_map_[i] = 0;
false_map_[i] = 0;
}
}
~AXBitMap() = default;
// Returns whether enum T at |value| is set to true, false or unset.
absl::optional<bool> Has(const T enum_value) {
auto [value_position, true_map, false_map] = GetPositionAndMaps(enum_value);
const bool is_in_true_map = (*true_map) >> value_position & 1ull;
const bool is_in_false_map = (*false_map) >> value_position & 1ull;
CHECK(!(is_in_true_map && is_in_false_map))
<< std::string("A value can't be true and false at the same time.");
if (is_in_true_map) {
return true;
}
if (is_in_false_map) {
return false;
}
return absl::nullopt;
}
// Sets the enum T at |enum_value| to true or false.
void Set(const T enum_value, const bool bool_value) {
auto [value_position, true_map, false_map] = GetPositionAndMaps(enum_value);
uint64_t* map_to_set_true;
uint64_t* map_to_set_false;
if (bool_value) {
map_to_set_true = true_map;
map_to_set_false = false_map;
} else {
map_to_set_true = false_map;
map_to_set_false = true_map;
}
*map_to_set_true |= 1ull << value_position;
*map_to_set_false &= ~(1ull << value_position);
}
// Unsets the enum T at |enum_value|. If it is not set, this is a no-op.
void Unset(const T enum_value) {
auto [value_position, true_map, false_map] = GetPositionAndMaps(enum_value);
(*true_map) &= ~(1ull << value_position);
(*false_map) &= ~(1ull << value_position);
}
private:
// Helper function that returns a tuple with the position of the value in the
// maps, a pointer to the correct bucket in |true_map_| and |false_map_|.
std::tuple<uint64_t, uint64_t*, uint64_t*> GetPositionAndMaps(const T value) {
uint64_t absolute_value_position = static_cast<uint64_t>(value);
const size_t map_bucket = absolute_value_position / kElementsPerMapBucket;
uint64_t* true_map = &(true_map_[map_bucket]);
uint64_t* false_map = &(false_map_[map_bucket]);
// Subtracts map_bucket * 64 from |value_position| so that it references the
// correct place in the map variables.
uint64_t relative_value_position =
absolute_value_position - map_bucket * kElementsPerMapBucket;
return {relative_value_position, true_map, false_map};
}
// Indicates that the enum T is true at the bit shifted value. This array
// holds 64 enum values per position, and will contains as many entries to
// hold all enum possible values.
uint64_t true_map_[static_cast<size_t>(
static_cast<size_t>(T::kMaxValue) / kElementsPerMapBucket + 1)];
// Indicates that the enum T is false at the bit shifted value. This array
// holds 64 enum values per position, and will contains as many entries to
// hold all enum possible values.
uint64_t false_map_[static_cast<size_t>(
static_cast<size_t>(T::kMaxValue) / kElementsPerMapBucket + 1)];
// Undefined/unset implied by not in *_true and *_false;
};
} // namespace ui
#endif // UI_ACCESSIBILITY_AX_BIT_MAP_H_
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