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/*
* Copyright 2020 WebAssembly Community Group participants
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef wasm_support_space_h
#define wasm_support_space_h
#include "utilities.h"
#include <wasm.h>
namespace wasm {
struct DisjointSpans {
// A span of form [a, b), i.e., that does not include the end point.
struct Span {
Address left, right;
bool checkOverlap(const Span& other) const {
return !(left >= other.right || right <= other.left);
}
};
struct SortByLeft {
bool operator()(const Span& left, const Span& right) const {
return left.left < right.left ||
(left.left == right.left && left.right < right.right);
}
};
// The spans seen so far. Guaranteed to be disjoint.
std::set<Span, SortByLeft> spans;
// Adds an item and checks overlap while doing so, returning true if such
// overlap exists.
bool addAndCheckOverlap(Span span) {
// Insert the new span. We can then find its predecessor and successor.
// They are disjoint by assumption, so the question is then does the new
// span overlap with them, or not.
auto [iter, inserted] = spans.insert(span);
if (!inserted) {
// This exact span was already there, so there is definite overlap.
return true;
}
// Check predecessor and successor, if they exist.
if (iter != spans.begin() && std::prev(iter)->checkOverlap(span)) {
return true;
}
if (std::next(iter) != spans.end() && std::next(iter)->checkOverlap(span)) {
return true;
}
return false;
}
// Inefficient - mostly for testing.
void add(Span span) { addAndCheckOverlap(span); }
// Inefficient - mostly for testing.
bool checkOverlap(Span span) {
bool existsBefore = spans.find(span) != spans.end();
auto hasOverlap = addAndCheckOverlap(span);
if (!existsBefore) {
spans.erase(span);
}
return hasOverlap;
}
};
} // namespace wasm
#endif // wasm_support_space_h
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