Re: [Sbcl-devel] 64-bit modular arithmetic on intel 64-bit + ubuntu

[Jan M. <jmo...@te...>]

On Sat, 2013-11-09 at 10:25 -0500, Douglas Katzman wrote:
> Nice code, but at a glance I can see that your problem is that the global
> symbol *R* is used as your generator state, therefore forcing
> materialization of all potential bignums.
> I hacked it up a little bit and halved the runtime of (bench 50000000).
> 
> In practice, you should make a macro
>   (WITH-GENERATOR (R) ...)
> which expands to provide UNIFORM_REAL, UNIFORM_NAT, UNIFORM_BIT as lexical
> macros within its body.
> ("Do as I say, not as I do")
> 
> Attached diffs will get you started.

When noticing the defvar, I had a similar idea. I went with local
functions which, on my system, also achieved halving the runtime (and
consing):

(defun compiled-mcmc/local-functions (N)
  (flet ((make-generator () (logand 8682522807148012 +mask+)))
    (let ((r (make-generator)))
      (labels ((random_next (r)
		 (logand (+ (* r +multiplier+) +addend+) +mask+))
	       (uniform_bit ()
		 (logand (select  (setf r (random_next r)) 1) 1))
	       (->double/52 (r)
		 (/ (ash r (- 52 +width+)) +expt-2-52d0+))
	       (uniform_real ()
		 (->double/52 (setf r (random_next r)))))
	UNMODIFIED-REST-OF-THE-BODY))))

Kind regards,
Jan