[v9,9/9] manual: Add documentation for arc4random functions
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From: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
---
manual/math.texi | 45 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 45 insertions(+)
Comments
Adhemerval Zanella via Libc-alpha wrote:
> 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}
s/reseed/reseeded/
> +and @code{_Fork}. It is not cleared for either direct @code{clone} syscall
s/for either/on either a/
> +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)
s/int32_t/uint32_t/
> +@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})
s/arc4random/arc4random_buf/
> +@standards{BSD, stdlib.h}
> +@safety{@mtsafe{}@asunsafe{@asucorrupt{}}@acsafe{}}
> +This function fills the region @var{buffer} of @var{length} with random data.
s/of @var{length}/of length @var{length} bytes/
> +@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
>
On 14/07/22 07:03, Mark Harris wrote:
> Adhemerval Zanella via Libc-alpha wrote:
>> 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}
>
> s/reseed/reseeded/
Ack.
>
>> +and @code{_Fork}. It is not cleared for either direct @code{clone} syscall
>
> s/for either/on either a/
>
>> +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)
>
> s/int32_t/uint32_t/
Ack.
>
>> +@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})
>
> s/arc4random/arc4random_buf/
Ack.
>
>> +@standards{BSD, stdlib.h}
>> +@safety{@mtsafe{}@asunsafe{@asucorrupt{}}@acsafe{}}
>> +This function fills the region @var{buffer} of @var{length} with random data.
>
> s/of @var{length}/of length @var{length} bytes/
Ack.
>
>
>> +@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
>>
@@ -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