michael@0: /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
michael@0: /* vim: set ts=8 sts=2 et sw=2 tw=80: */
michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: #ifndef mozilla_BinarySearch_h
michael@0: #define mozilla_BinarySearch_h
michael@0: 
michael@0: #include "mozilla/Assertions.h"
michael@0: 
michael@0: #include <stddef.h>
michael@0: 
michael@0: namespace mozilla {
michael@0: 
michael@0: /*
michael@0:  * The algorithm searches the given container 'c' over the sorted index range
michael@0:  * [begin, end) for an index 'i' where 'c[i] == target'. If such an index 'i' is
michael@0:  * found, BinarySearch returns 'true' and the index is returned via the outparam
michael@0:  * 'matchOrInsertionPoint'. If no index is found, BinarySearch returns 'false'
michael@0:  * and the outparam returns the first index in [begin, end] where 'target' can
michael@0:  * be inserted to maintain sorted order.
michael@0:  *
michael@0:  * Example:
michael@0:  *
michael@0:  *   Vector<int> sortedInts = ...
michael@0:  *
michael@0:  *   size_t match;
michael@0:  *   if (BinarySearch(sortedInts, 0, sortedInts.length(), 13, &match))
michael@0:  *     printf("found 13 at %lu\n", match);
michael@0:  */
michael@0: 
michael@0: template <typename Container, typename T>
michael@0: bool
michael@0: BinarySearch(const Container &c, size_t begin, size_t end, T target, size_t *matchOrInsertionPoint)
michael@0: {
michael@0:   MOZ_ASSERT(begin <= end);
michael@0: 
michael@0:   size_t low = begin;
michael@0:   size_t high = end;
michael@0:   while (low != high) {
michael@0:     size_t middle = low + (high - low) / 2;
michael@0:     const T &middleValue = c[middle];
michael@0: 
michael@0:     MOZ_ASSERT(c[low] <= c[middle]);
michael@0:     MOZ_ASSERT(c[middle] <= c[high - 1]);
michael@0:     MOZ_ASSERT(c[low] <= c[high - 1]);
michael@0: 
michael@0:     if (target == middleValue) {
michael@0:       *matchOrInsertionPoint = middle;
michael@0:       return true;
michael@0:     }
michael@0: 
michael@0:     if (target < middleValue)
michael@0:       high = middle;
michael@0:     else
michael@0:       low = middle + 1;
michael@0:   }
michael@0: 
michael@0:   *matchOrInsertionPoint = low;
michael@0:   return false;
michael@0: }
michael@0: 
michael@0: } // namespace mozilla
michael@0: 
michael@0: #endif // mozilla_BinarySearch_h