Re: [PATCH] atm: he: fix sign-extension overflow on large shift

From: Dan Carpenter
Date: Wed Jan 16 2019 - 03:51:20 EST


On Tue, Jan 15, 2019 at 06:03:38PM +0000, Colin King wrote:
> From: Colin Ian King <colin.king@xxxxxxxxxxxxx>
>
> Shifting the 1 by exp by an int can lead to sign-extension overlow when
> exp is 31 since 1 is an signed int and sign-extending this result to an
> unsigned long long will set the upper 32 bits. Fix this by shifting an
> unsigned long.

You could just cast it to unsigned.

rate_cps = (unsigned long long) (1U << exp) * (man + 512) >> 9;

I don't think it makes a difference at runtime because we just
pick buf = 4 either way...

regards,
dan carpenter