`On Sat, Jan 19, 2019 at 04:14:50PM +0100, Florian La Roche wrote:> If an input number x for int_sqrt() has the highest bit set, then> __ffs(x) is 64. (1UL << 64) is an overflow and breaks the algorithm.This is confusing, because the patch doesn't go near an __ffs().> Just subtracting 1 is an even better guess for the initial> value of m and that's what also used to be done in earlier> versions of this code.> > best regards,> > Florian La Roche> > Signed-off-by: Florian La Roche <Florian.LaRoche@googlemail.com>> --->  lib/int_sqrt.c | 4 ++-->  1 file changed, 2 insertions(+), 2 deletions(-)> > diff --git a/lib/int_sqrt.c b/lib/int_sqrt.c> index 14436f4ca6bd..ea00e84dc272 100644> --- a/lib/int_sqrt.c> +++ b/lib/int_sqrt.c> @@ -23,7 +23,7 @@ unsigned long int_sqrt(unsigned long x)>  	if (x <= 1)>  		return x;> > -	m = 1UL << (__fls(x) & ~1UL);> +	m = 1UL << ((__fls(x) - 1) & ~1UL);I think this one is fine, because __fls() gives you back 0-63 (orundefined, but the previous <= 1 check handles that case).>  	while (m != 0) {>  		b = y + m;>  		y >>= 1;> @@ -52,7 +52,7 @@ u32 int_sqrt64(u64 x)>  	if (x <= ULONG_MAX)>  		return int_sqrt((unsigned long) x);> > -	m = 1ULL << (fls64(x) & ~1ULL);> +	m = 1ULL << ((fls64(x) - 1) & ~1ULL);This just looks like a copy-paste error because there isn't an __fls64().But I think your suggestion here is ok, given the previous check againstULONG_MAX.Will`