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Subject[PATCH] trivial, document that div64_u64() is not precise on 32bit platforms
We have a bugreport which blames div64_u64() on 32bit platforms.

However, the code obviously doesn't even try to pretend it can do
the 64bit division precisely. If there is something in the high
word of divisor, div64_u64() just shifts both arguments and throws
out the low bits.

Add a small comment to avoid the confusion.

Signed-off-by: Oleg Nesterov <>

lib/div64.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

--- a/lib/div64.c
+++ b/lib/div64.c
@@ -77,7 +77,10 @@ s64 div_s64_rem(s64 dividend, s32 diviso

-/* 64bit divisor, dividend and result. dynamic precision */
+ * 64bit divisor, dividend and result. Dynamic precision, unless
+ * divisor fits in u32 result is not exactly correct.
+ */
#ifndef div64_u64
u64 div64_u64(u64 dividend, u64 divisor)

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