[PATCH v1 3/5] random: add helpers for random numbers with given floor or range
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: 2022-10-22 01:44:44
Also in:
linux-arm-kernel, linux-block, linux-crypto, linux-fsdevel, linux-media, linux-mips, linux-mmc, linux-patches, linuxppc-dev, lkml, loongarch
Subsystem:
random number driver, the rest · Maintainers:
"Theodore Ts'o", Jason A. Donenfeld, Linus Torvalds
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@zx2c4.com> --- 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); +} + /* * On 64-bit architectures, protect against non-terminated C string overflows * by zeroing out the first byte of the canary; this leaves 56 bits of entropy.
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2.38.1