Re: [ft-devel] those OVERFLOW_* macros and Fontval b69 (Re: Freetype-devel Digest, Vol 149, Issue 5

[Markus Trippelsdorf]

On 2017.06.05 at 05:56 +0200, Werner LEMBERG wrote:
> 
> >> Ditto for bytecode.  Checking every addition, subtraction or
> >> multiplication for overflow is something I want to avoid,
> > 
> > Of course, I am only suggesting rejecting input with unreasonably
> > large coordinates or metric values.
> 
> This would be ideal, yes, but I don't see how you can do that.  For
> example, it makes sense to reject, say, PCF properties that exceed the
> value 0x7FFF (I added such tests recently).  Similar things can be
> done for other format too.  However, the majority of input data in
> most formats are deltas, and here you would have to check after every
> addition, subtraction, or multiplication whether you get something
> `unreasonable'.

BTW are you aware of gcc's and clang's built-in functions that perform
arithmetic with overflow checking? Maybe they could help.
https://gcc.gnu.org/onlinedocs/gcc/Integer-Overflow-Builtins.html

-- 
Markus