[FFmpeg-cvslog] r21069 - trunk/libavcodec/alsdec.c

[Måns Rullgård]

Uoti Urpala <uoti.urpala at pp1.inet.fi> writes:

> On Sat, 2010-01-09 at 12:42 +0000, M?ns Rullg?rd wrote:
>> OK, here's what's happening.
>> 
>> When opt_order is unsigned, the expression -opt_order has a (large)
>> positive value obtained by wrapping the mathematical negation of
>> opt_order into the proper number of bits (32 here).  The type of the
>> expression is still unsigned.  When an out of range value is assigned
>> to a signed type, the result is undefined.  Most compilers seem to
>
> Wrong. Overflow in signed arithmetic would be undefined, but converting
> a value to a signed integer type when the value cannot be represented in
> that type is implementation-defined behavior. GCC defines that the value
> is reduced modulo 2^N (N=width of the type). If GCC 4.1 behaves as
> described that is a bug which goes against defined behavior.

Undefined or implementation-defined, it's a bad thing to be doing.

-- 
M?ns Rullg?rd
mans at mansr.com