[vlc-devel] [PATCH 3/7] subsdec: fix potential unsigned overflow

Rémi Denis-Courmont remi at remlab.net
Tue May 6 22:44:48 CEST 2014

Le mardi 6 mai 2014, 22:28:04 Felix Abecassis a écrit :
> > If psz_tag is the empty string the result is unchanged.
> Is it? Unsigned overflow is well defined but conversion of an out of
> range unsigned value to a signed value is implementation defined
> apparently.

Well yeah. In ISO, it is implementation-defined. GCC defines it to do the Right 
Thing though, as, I believe, any other real-life C compiler:

   * `The result of, or the signal raised by, converting an integer to a
     signed integer type when the value cannot be represented in an
     object of that type (C90, C99'

     For conversion to a type of width N, the value is reduced modulo
     2^N to be within range of the type; no signal is raised.

You are allowed to be pedantic and ignore that GCC statement. But then, 
converting to size_t to int is also implementation-defined as size_t may be 
larger than int. So the patch does not really fix the theoretical problem.

Rémi Denis-Courmont

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