gecko/mfbt/BinarySearch.h

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/* -*- 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/. */
#ifndef mozilla_BinarySearch_h
#define mozilla_BinarySearch_h
#include "mozilla/Assertions.h"
#include <stddef.h>
namespace mozilla {
/*
* The algorithm searches the given container |aContainer| over the sorted
* index range [aBegin, aEnd) for an index |i| where |aContainer[i] == aTarget|.
* If such an index |i| is found, BinarySearch returns |true| and the index is
* returned via the outparam |aMatchOrInsertionPoint|. If no index is found,
* BinarySearch returns |false| and the outparam returns the first index in
* [aBegin, aEnd] where |aTarget| can be inserted to maintain sorted order.
*
* Example:
*
* Vector<int> sortedInts = ...
*
* size_t match;
* if (BinarySearch(sortedInts, 0, sortedInts.length(), 13, &match))
* printf("found 13 at %lu\n", match);
*/
template <typename Container, typename T>
bool
BinarySearch(const Container& aContainer, size_t aBegin, size_t aEnd,
T aTarget, size_t* aMatchOrInsertionPoint)
{
MOZ_ASSERT(aBegin <= aEnd);
size_t low = aBegin;
size_t high = aEnd;
while (low != high) {
size_t middle = low + (high - low) / 2;
// Allow any intermediate type so long as it provides a suitable ordering
// relation.
const auto& middleValue = aContainer[middle];
MOZ_ASSERT(aContainer[low] <= aContainer[middle]);
MOZ_ASSERT(aContainer[middle] <= aContainer[high - 1]);
MOZ_ASSERT(aContainer[low] <= aContainer[high - 1]);
if (aTarget == middleValue) {
*aMatchOrInsertionPoint = middle;
return true;
}
if (aTarget < middleValue) {
high = middle;
} else {
low = middle + 1;
}
}
*aMatchOrInsertionPoint = low;
return false;
}
} // namespace mozilla
#endif // mozilla_BinarySearch_h