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

[Uoti Urpala]

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.