[libvirt] [PATCH v2] Add virRandom() API to generate numbers with non-power-of-2 limit

[Eric Blake]

On 08/14/2012 05:13 AM, Daniel P. Berrange wrote:
> From: "Daniel P. Berrange" <berrange at redhat.com>
> 
> The current virRandomBits() API is only usable if the caller wants
> a random number in the range [0, (n-1)] where n is a power of two.

This one is correct (it could also be written '[0, n)').

> This adds a virRandom() API which generates a double in the
> range [0.0,1.0] with 48 bits of entropy. It then also adds a

s/]/)/ (the range includes 0.0, but excludes 1.0)

> virRandomInt(uint32_t max) API which generates an unsigned
> in the range [0, at max]

s/]/)/ (the range includes 0, but excludes @max; it could also be
written '[0, at max-1]')

> 
> Signed-off-by: Daniel P. Berrange <berrange at redhat.com>
> ---
>  src/libvirt_private.syms |  2 ++
>  src/util/virrandom.c     | 32 ++++++++++++++++++++++++++++++++
>  src/util/virrandom.h     |  2 ++
>  3 files changed, 36 insertions(+)

> +++ b/src/util/virrandom.c
> @@ -23,6 +23,7 @@
>  
>  #include <stdlib.h>
>  #include <inttypes.h>
> +#include <math.h>

Hmm, the gnulib module 'ldexp' is currently LGPLv3+, but then again,
gnulib doesn't document any glaring issues fixed by the module, other
than the module provides $(LDEXP_LIBM) as a handy way to decide in
Makefile.am whether to link against -lm or not (some libc provide ldexp
without -lm, other platforms require the extra library).  Gnulib also
provides the module 'ldexp-ieee', to fix platforms with broken handling
of NaN, but we don't care about NaN in our usage.

I'll ask on gnulib about whether the license of 'ldexp' can be relaxed;
if Bruno agrees, then I'll do a followup patch to pull in that module.
In the meantime, I don't have any objections to how you are using
ldexp(), as long as you cross-compiled to mingw without issues.

> 
> +/**
> + * virRandom:
> + *
> + * Generate an evenly distributed random number between [0.0,1.0]

Same conversion of ] to ) as in the commit message.

> +/**
> + * virRandomInt32:

s/32// - you must have changed the function name between documenting it
and implementing it.

> + * @max: upper limit
> + *
> + * Generate an evenly distributed random integer between [0, at max]
> + *
> + * Return: a random number between [0, at max]

Same conversion of ] to ) as in the commit message.

ACK with those spelling nits fixed.

-- 
Eric Blake   eblake at redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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