std::vector::_Reserve() contains a suboptimal check against max_size by Dmitry Me

As of version 10.0.40219.1 SP1Rel std::vector::_Reserve() code goes like this:

if (max_size() - _Count < _Size)
_Xlen();
else if ((_Size += _Count) <= capacity())
;
else
reserve(_Grow_to(_Size));
}

Now capacity() <= max_size() at all times. Which means that if capacity() >= _Size + _Count (enough room) then automatically max_size() >= _Size + _Count. Which means that whenever that code is invoked when a vector already has room (that's quite often) the check max_size() >= _Size() + _Count is redundant.

_Reserve() should be redesigned like this:

if (capacity() - _Size >= _Count)
;//enough room - do nothing
else if( (max_size() - _Size < _Count)
_Xlen();
else
{
     reserve(_Grow_to( _Size+_Count));
}

so that the check is done only if there's a need for reallocation in the first place.