c/7284: incorrectly simplifies leftshift followed by signed power-of-2 division

Falk Hueffner falk.hueffner@student.uni-tuebingen.de
Fri Jul 12 10:05:00 GMT 2002

"Al Grant" <AlGrant@myrealbox.com> writes:

> 3.3.7 (something else in ISO, maybe 6.3.7)
>   The result of E1 << E2 is E1 left-shifted E2 bit
>   positions; vacated bits are filled with zeros.
> For signed types it says nothing more.
> Now if signed left-shift is defined at all, in terms of the
> representation, I don't see there's any lack of definition in
> "0x00000080 left-shifted 24 bit positions", it is clearly 0x80000000
> (of the same type).  So it's defined unless the standard says
> otherwise, which only C99 seems to.

Defect Report #081 seems to be of interest here
(http://wwwold.dkuug.dk/JTC1/SC22/WG14/www/docs/dr_081.html). It
basically states that the behaviour is implementation defined (for any
signed left shift, not just this case).


More information about the Gcc-bugs mailing list