On 08/10/2012 08:58 AM, Eric Blake wrote:
On 08/10/2012 07:47 AM, Daniel P. Berrange wrote:
From: "Daniel P. Berrange" <berrange@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 adds a virRandom() API which works for upper limits which are not a power of two. It works by using virRandomBits() to generate a number to the next nearest power of 2 limit, and then scales it down.
+ + while (tmp) { + tmp >>= 1; + bits++; + }
Slow. I would suggest using gcc's __builtin_clz (the way qemu does), except that gnulib doesn't yet have a module exposing it. I guess that means I'd better write a quick gnulib module. Once you have clz(), this is much simpler as:
assert(max); bits = 64 - clz(max);
Gnulib side is done. If you apply this patch to libvirt (including an update to the latest gnulib), then you can #include "count-leading-zeros.h" and call count_leading_zeros_ll(max) (spelled that way in gnulib rather than clz to minimize potential clashes, since it is not a standardized function). diff --git i/.gnulib w/.gnulib index dbd9144..0da76a9 160000 --- i/.gnulib +++ w/.gnulib @@ -1 +1 @@ -Subproject commit dbd914496c99c52220e5f5ba4121d6cb55fb3beb +Subproject commit 0da76a94c8668319c68af5e8c2e71c80528db5de diff --git i/bootstrap.conf w/bootstrap.conf index c112ccd..58558c8 100644 --- i/bootstrap.conf +++ w/bootstrap.conf @@ -33,6 +33,7 @@ chown close connect configmake +count-leading-zeros count-one-bits crypto/md5 dirname-lgpl -- Eric Blake eblake@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org