gecko-dev/mfbt/BinarySearch.h

67 lines
1.8 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/. */
#ifndef mozilla_BinarySearch_h
#define mozilla_BinarySearch_h
#include "mozilla/Assertions.h"
#include <stddef.h>
namespace mozilla {
/*
* The algorithm searches the given container 'c' over the sorted index range
* [begin, end) for an index 'i' where 'c[i] == target'. If such an index 'i' is
* found, BinarySearch returns 'true' and the index is returned via the outparam
* 'matchOrInsertionPoint'. If no index is found, BinarySearch returns 'false'
* and the outparam returns the first index in [begin, end] where 'target' 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 &c, size_t begin, size_t end, T target, size_t *matchOrInsertionPoint)
{
MOZ_ASSERT(begin <= end);
size_t low = begin;
size_t high = end;
while (low != high) {
size_t middle = low + (high - low) / 2;
const T &middleValue = c[middle];
MOZ_ASSERT(c[low] <= c[middle]);
MOZ_ASSERT(c[middle] <= c[high - 1]);
MOZ_ASSERT(c[low] <= c[high - 1]);
if (target == middleValue) {
*matchOrInsertionPoint = middle;
return true;
}
if (target < middleValue)
high = middle;
else
low = middle + 1;
}
*matchOrInsertionPoint = low;
return false;
}
} // namespace mozilla
#endif // mozilla_BinarySearch_h