Re: Issue 4212: fix out-of-bounds index in division_maior() (issue 189420043 by address@hidden)

[dak]

On 2015/01/02 14:16:54, Dan Eble wrote:
> On 2015/01/02 08:56:03, dak wrote:
> > In particular, the compiler is allowed to make
> > line_pos.begin () < whatever the same as line_pos.begin () !=
whatever.

> * std::vector elements must be contiguous after C++03
> (http://en.cppreference.com/w/cpp/container/vector)
> * it[n] is convertible to a reference and is equivalent to *(i + n)
> (http://en.cppreference.com/w/cpp/concept/RandomAccessIterator)

> Therefore there should be no problem with "x.begin() < it" as long as
the vector
> is not empty and "it != x.end()".  I'm not sure if anything constrains
the
> implementation of x.end() to refer to the place this code assumes it
does, so
> that might still be a problem.

> Still, I'm going to resist doing anything other than fixing the
immediate
> problem.  I do not want to risk spending a bunch of time debugging if
I rewrite
> it wrong.

The case I was worried about was (line_pos.begin () < it - 1)
This expression is undefined if it == line_pos.begin () since
line_pos.begin () - 1 is undefined, being before the start of the array.

https://codereview.appspot.com/189420043/