| commit | c622ac1b8662908b595ec1a19e401ad6a629f52c | |
| author | Adhemerval Zanella <adhemerval.zanella@linaro.org> | |
| Thu, 28 Jul 2022 12:18:01 +0000 (28 09:18 -0300) | ||
| committer | Adhemerval Zanella <adhemerval.zanella@linaro.org> | |
| Mon, 1 Aug 2022 17:37:24 +0000 (1 14:37 -0300) | ||
| tree | 3f45901eabfdbcb7688b68d22f8cf55d07eaf4c1 | treesnapshot (tar.gz zip) |
| parent | 7187efd0aa270c83c428ea6cd0e1cffc34b41a74 | commitdiff |
stdlib: Simplify arc4random_uniform
It uses the bitmask with rejection [1], which calculates a mask
being the lowest power of two bounding the request upper bound,
successively queries new random values, and rejects values
outside the requested range.
Performance-wise, there is no much gain in trying to conserve
bits since arc4random is wrapper on getrandom syscall. It should
be cheaper to just query a uint32_t value. The algorithm also
avoids modulo and divide operations, which might be costly
depending of the architecture.
[1] https://www.pcg-random.org/posts/bounded-rands.html
Reviewed-by: Yann Droneaud <ydroneaud@opteya.com>
It uses the bitmask with rejection [1], which calculates a mask
being the lowest power of two bounding the request upper bound,
successively queries new random values, and rejects values
outside the requested range.
Performance-wise, there is no much gain in trying to conserve
bits since arc4random is wrapper on getrandom syscall. It should
be cheaper to just query a uint32_t value. The algorithm also
avoids modulo and divide operations, which might be costly
depending of the architecture.
[1] https://www.pcg-random.org/posts/bounded-rands.html
Reviewed-by: Yann Droneaud <ydroneaud@opteya.com>
| stdlib/arc4random_uniform.c | diffblobblamehistory |