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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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 BinarySearch() 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);
* }
*
* The BinarySearchIf() version behaves similarly, but takes |aComparator|, a
* functor to compare the values with, instead of a value to find.
* That functor should take one argument - the value to compare - and return an
* |int| with the comparison result:
*
* * 0, if the argument is equal to,
* * less than 0, if the argument is greater than,
* * greater than 0, if the argument is less than
*
* the value.
*
* Example:
*
* struct Comparator {
* int operator()(int aVal) const {
* if (mTarget < aVal) { return -1; }
* if (mTarget > aVal) { return 1; }
* return 0;
* }
* explicit Comparator(int aTarget) : mTarget(aTarget) {}
* const int mTarget;
* };
*
* Vector<int> sortedInts = ...
*
* size_t match;
* if (BinarySearchIf(sortedInts, 0, sortedInts.length(), Comparator(13), &match)) {
* printf("found 13 at %lu\n", match);
* }
*
*/
template<typename Container, typename Comparator>
bool
BinarySearchIf(const Container& aContainer, size_t aBegin, size_t aEnd,
const Comparator& aCompare, size_t* aMatchOrInsertionPoint)
{
MOZ_ASSERT(aBegin <= aEnd);
size_t low = aBegin;
size_t high = aEnd;
while (high != low) {
size_t middle = low + (high - low) / 2;
// Allow any intermediate type so long as it provides a suitable ordering
// relation.
const int result = aCompare(aContainer[middle]);
if (result == 0) {
*aMatchOrInsertionPoint = middle;
return true;
}
if (result < 0) {
high = middle;
} else {
low = middle + 1;
}
}
*aMatchOrInsertionPoint = low;
return false;
}
namespace detail {
template<class T>
class BinarySearchDefaultComparator
{
public:
explicit BinarySearchDefaultComparator(const T& aTarget)
: mTarget(aTarget)
{}
template <class U>
int operator()(const U& aVal) const {
if (mTarget == aVal) {
return 0;
}
if (mTarget < aVal) {
return -1;
}
return 1;
}
private:
const T& mTarget;
};
} // namespace detail
template <typename Container, typename T>
bool
BinarySearch(const Container& aContainer, size_t aBegin, size_t aEnd,
T aTarget, size_t* aMatchOrInsertionPoint)
{
return BinarySearchIf(aContainer, aBegin, aEnd,
detail::BinarySearchDefaultComparator<T>(aTarget),
aMatchOrInsertionPoint);
}
} // namespace mozilla
#endif // mozilla_BinarySearch_h
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