[resent in text only]
Hi,
Le 22/10/2022 à 03:44, Jason A. Donenfeld a écrit :
Now that we have get_random_u32_below(), it's trivial to make inline
helpers to compute get_random_u32_above() and get_random_u32_between(),
which will help clean up open coded loops and manual computations
throughout the tree.
Signed-off-by: Jason A. Donenfeld<Jason@xxxxxxxxx>
---
include/linux/random.h | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)
diff --git a/include/linux/random.h b/include/linux/random.h
index 3a82c0a8bc46..92188a74e50e 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -91,6 +91,30 @@ static inline u32 get_random_u32_below(u32 ceil)
}
}
+/*
+ * Returns a random integer in the interval (floor, U32_MAX], with uniform
+ * distribution, suitable for all uses. Fastest when floor is a constant, but
+ * still fast for variable floor as well.
+ */
+static inline u32 get_random_u32_above(u32 floor)
+{
+ BUILD_BUG_ON_MSG(__builtin_constant_p(floor) && floor == U32_MAX,
+ "get_random_u32_above() must take floor < U32_MAX");
+ return floor + 1 + get_random_u32_below(U32_MAX - floor);
+}
+
+/*
+ * Returns a random integer in the interval [floor, ceil), with uniform
+ * distribution, suitable for all uses. Fastest when floor and ceil are
+ * constant, but still fast for variable floor and ceil as well.
+ */
+static inline u32 get_random_u32_between(u32 floor, u32 ceil)
+{
+ BUILD_BUG_ON_MSG(__builtin_constant_p(floor) && __builtin_constant_p(ceil) &&
+ floor >= ceil, "get_random_u32_above() must take floor < ceil");
+ return floor + get_random_u32_below(ceil - floor);
+}
I have a bad feeling about this one, and can't help but thinking it's going
to bite someone: when asked to pick a number *between* 0 and 10,
I usually think I'm allowed to pick 10 (even if I'm going to answer 7 as it should).
Also, regardinghttps://lore.kernel.org/lkml/20221114164558.1180362-4-Jason@xxxxxxxxx/
where there's a lot of such changes:
- seqno = get_random_u32_below(data->fc.chain_length) + 1; + seqno =
get_random_u32_between(1, data->fc.chain_length + 1); IMHO, having the
function returning a value in range [floor, ceil] would simplify the
patch: - seqno = get_random_u32_below(data->fc.chain_length) + 1; +
seqno = get_random_u32_between(1, data->fc.chain_length);
Regards.
--
Yann Droneaud
OPTEYA