[erlang-questions] Extending term external format to support shared substructures

[Bjorn Gustavsson]

On Tue, Mar 31, 2009 at 12:00 PM, Matthew Dempsky <matthew@REDACTED> wrote:
>
> Here's what I get with my patched R13A:
>
>    > binary_to_term(<<131,104,2,108,0,0,0,0,106,100,0,1,97>>).
>    {[],a}
>
> Do you get something different?  Is this not what you think it should be?

My fault. I did not apply the patch correctly (I manually applied only the
correction for this issue, because I didn't want the rest of the patch).
Your correction works fine and I will use your correction (my correction
used a goto).

>
>> To make sure that all terms are properly nested. We try to do as much error
>> checking as possible while calculating the size.
>
> Sorry, I still don't see the benefit.  E.g., what better error
> checking do you have right now than if in the clause for
> SMALL_TUPLE_EXT you were to replace
>
>    ESTACK_PUSH(s, terms);
>    terms = *ep++;
>    heap_size += terms + 1;
>
> with
>
>    n = *ep++;
>    terms += n;
>    heap_size += n + 1;
>
>
> ?  With the exception of overflowing the 'terms' counter (which can be
> easily resolved by changing it to a 64-bit integer), I don't see how
> the former ends up being any stricter than the latter.

You are probably right. I applied your change and ran a test suite with contains
many examples of corrupt external format. It did not fail.

I will have to think more about it. If I can't find any reason for the
pushing and
popping, I will change it in R13B.

/Bjorn

-- 
Björn Gustavsson, Erlang/OTP, Ericsson AB