/**
* Copyright (C) 2015 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see .
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#include "mongo/platform/basic.h"
#include "mongo/platform/stack_locator.h"
#include "mongo/util/assert_util.h"
namespace mongo {
boost::optional StackLocator::available() const {
if (!begin() || !end())
return boost::none;
// Technically, it is undefined behavior to compare or subtract
// two pointers that do not point into the same
// aggregate. However, we know that these are both pointers within
// the same stack, and it seems unlikely that the compiler will
// see that it can elide the comparison here.
const auto cbegin = reinterpret_cast(begin());
const auto cthis = reinterpret_cast(this);
const auto cend = reinterpret_cast(end());
// TODO: Assumes that stack grows downward
invariant(cthis <= cbegin);
invariant(cthis > cend);
std::size_t avail = cthis - cend;
return avail;
}
boost::optional StackLocator::size() const {
if (!begin() || !end())
return boost::none;
const auto cbegin = reinterpret_cast(begin());
const auto cend = reinterpret_cast(end());
// TODO: Assumes that stack grows downward
invariant(cbegin > cend);
return static_cast(cbegin - cend);
}
} // namespace mongo