out-of-line and arch-specific random_device

[Ulrich Drepper]

On Tue, Aug 28, 2012 at 4:44 AM, Paolo Carlini <paolo.carlini@oracle.com> wrote:
> Again, without context, I think this is not the point: random_device is meant to be just a simple high level wrapper
> around things like dev/random, inspired by facilities like dev/random on unix-like OSes. The brutal "fall back" we have
> now in place wouldn't be useful anyway for the uses Marc is talking about, because there is no way to provide a seed.
> That said, I can't check right now C++11 about random_device, I suppose Uli has already ;)

I did read it.  random_device is all about non-determinism.  Of course
I know that RNGs in some situations have to be repeatable.  That's
what all the engines are about.  random_device isn't.  You use
random_device to seed an engine etc.

The spec says that if there is no way to create non-deterministic data
the implementation may use a random number engine.  "may" being to
key.


I perhaps didn't make myself clear as to what the big problem is.
Depending on whether or not you define _GLIBCXX_USE_RANDOM_TR1 you get
an object definition for 'random"device" which has the same name and
mangling but has a different size.  This means binary
incompatibilities.  Memory corruptions.

Combine that problem with the fact that there is no need to fall back
to pRNGs (and I'd argue it's really a bad idea because people expect
real entropy and won't get any with pRNGs) and I think that just
removing the pre-TR1 support will solve the issue nicely.