From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
To: libc-alpha@sourceware.org, Florian Weimer <fweimer@redhat.com>
Subject: [PATCH v9 9/9] manual: Add documentation for arc4random functions
Date: Wed, 13 Jul 2022 14:36:57 -0300 [thread overview]
Message-ID: <20220713173657.516725-10-adhemerval.zanella@linaro.org> (raw)
In-Reply-To: <20220713173657.516725-1-adhemerval.zanella@linaro.org>
From: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
---
manual/math.texi | 45 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 45 insertions(+)
diff --git a/manual/math.texi b/manual/math.texi
index 477a18b6d1..ab96726e57 100644
--- a/manual/math.texi
+++ b/manual/math.texi
@@ -1447,6 +1447,7 @@ systems.
* ISO Random:: @code{rand} and friends.
* BSD Random:: @code{random} and friends.
* SVID Random:: @code{drand48} and friends.
+* High Quality Random:: @code{arc4random} and friends.
@end menu
@node ISO Random
@@ -1985,6 +1986,50 @@ This function is a GNU extension and should not be used in portable
programs.
@end deftypefun
+@node High Quality Random
+@subsection High Quality Random Number Functions
+
+This section describes the random number functions provided as a GNU
+extension, based on OpenBSD interfaces.
+
+@Theglibc{} uses kernel entropy obtained either through @code{getrandom}
+or by reading @file{/dev/urandom} to seed and periodically re-seed the
+internal state. A per-thread data pool is used, which allows fast output
+generation.
+
+Although these functions provide higher random quality than ISO, BSD, and
+SVID functions, these still use a Pseudo-Random generator and should not
+be used in cryptographic contexts.
+
+The internal state is cleared and reseed with kernel entropy on @code{fork}
+and @code{_Fork}. It is not cleared for either direct @code{clone} syscall
+or when using @theglibc{} @code{syscall} function.
+
+The prototypes for these functions are in @file{stdlib.h}.
+@pindex stdlib.h
+
+@deftypefun int32_t arc4random (void)
+@standards{BSD, stdlib.h}
+@safety{@mtsafe{}@asunsafe{@asucorrupt{}}@acsafe{}}
+This function returns a single 32-bit value in the range of @code{0} to
+@code{2^32−1} (inclusive), which is twice the range of @code{rand} and
+@code{random}.
+@end deftypefun
+
+@deftypefun void arc4random (void *@var{buffer}, size_t @var{length})
+@standards{BSD, stdlib.h}
+@safety{@mtsafe{}@asunsafe{@asucorrupt{}}@acsafe{}}
+This function fills the region @var{buffer} of @var{length} with random data.
+@end deftypefun
+
+@deftypefun uint32_t arc4random_uniform (uint32_t @var{upper_bound})
+@standards{BSD, stdlib.h}
+@safety{@mtsafe{}@asunsafe{@asucorrupt{}}@acsafe{}}
+This function returns a single 32-bit value, uniformly distributed but
+less than the @var{upper_bound}. It avoids the @w{modulo bias} when the
+upper bound is not a power of two.
+@end deftypefun
+
@node FP Function Optimizations
@section Is Fast Code or Small Code preferred?
@cindex Optimization
--
2.34.1
next prev parent reply other threads:[~2022-07-13 17:37 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-13 17:36 [PATCH v9 0/9] Add arc4random support Adhemerval Zanella
2022-07-13 17:36 ` [PATCH v9 1/9] stdlib: Add arc4random, arc4random_buf, and arc4random_uniform (BZ #4417) Adhemerval Zanella
2022-07-13 17:36 ` [PATCH v9 2/9] stdlib: Add arc4random tests Adhemerval Zanella
2022-07-13 17:36 ` [PATCH v9 3/9] benchtests: Add arc4random benchtest Adhemerval Zanella
2022-07-13 17:36 ` [PATCH v9 4/9] aarch64: Add optimized chacha20 Adhemerval Zanella
2022-07-13 17:36 ` [PATCH v9 5/9] x86: Add SSE2 " Adhemerval Zanella
2022-07-13 18:12 ` Noah Goldstein
2022-07-13 18:20 ` Adhemerval Zanella Netto
2022-07-13 18:22 ` Noah Goldstein
2022-07-13 18:27 ` Noah Goldstein
2022-07-13 18:29 ` Adhemerval Zanella Netto
2022-07-13 18:53 ` Noah Goldstein
2022-07-13 17:36 ` [PATCH v9 6/9] x86: Add AVX2 " Adhemerval Zanella
2022-07-13 18:07 ` Noah Goldstein
2022-07-13 19:31 ` Adhemerval Zanella Netto
2022-07-13 20:24 ` Noah Goldstein
2022-07-13 20:16 ` Florian Weimer
2022-07-13 20:23 ` Noah Goldstein
2022-07-13 17:36 ` [PATCH v9 7/9] powerpc64: Add " Adhemerval Zanella
2022-07-13 17:36 ` [PATCH v9 8/9] s390x: " Adhemerval Zanella
2022-07-13 17:36 ` Adhemerval Zanella [this message]
2022-07-14 10:03 ` [PATCH v9 9/9] manual: Add documentation for arc4random functions Mark Harris
2022-07-14 11:08 ` Adhemerval Zanella Netto
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