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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.

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@xxxxxxxxxxxxxx>

---

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);

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);

while (m != 0) {

b = y + m;

y >>= 1;

--

2.17.1

**Next message:**Jiri Olsa: "Re: [RFC] Don't print sample_type bits in non-group events not set in the group's was Re: [PATCH] perf, script: Fix crash with printing mixed trace point and other events"**Previous message:**Martin Blumenstingl: "[PATCH v6 2/2] rtc: support for the Amlogic Meson RTC"**Next in thread:**Will Deacon: "Re: fix int_sqrt() for very large numbers"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]