Re: [Sbcl-devel] [Sbcl-commits] master: faster FIND and POSITION on bit-vectors

[Nathan F. <fr...@gm...>]

Great work!

On Thu, Dec 29, 2011 at 1:41 PM, Nikodemus Siivola
<de...@us...> wrote:
> diff --git a/src/code/bit-bash.lisp b/src/code/bit-bash.lisp
> index 7c7e539..909db1f 100644
> --- a/src/code/bit-bash.lisp
> +++ b/src/code/bit-bash.lisp
> @@ -594,3 +594,102 @@
>   (declare (type system-area-pointer sap))
>   (declare (type fixnum offset))
>   (copy-ub8-to-system-area bv 0 sap offset (length bv)))
> +
> +
> +;;;; Bashing-Style search for bits
> +;;;;
> +;;;; Similar search would work well for base-strings as well.
> +;;;; (Technically for all unboxed sequences of sub-word size elements,
> +;;;; but somehow I doubt other eg. octet vectors get POSIION or FIND

POSIION?  Typo.

> +                      (with-pinned-objects (vector)
> +                        (if from-end
> +                            ;; Back to front
> +                            (let* ((sap (vector-sap vector))
> +                                   (word-offset last-word)
> +                                   (word (logand end-mask (get-word sap word-offset))))

Is there a reason you're not using plain VECTOR-RAW-BITS here?  I
think it has the same effects, but you don't have to do all the
shifting and whatnot in GET-WORD.  And you wouldn't have to spuriously
pin things.  Depending on representation selection, I suppose you
could do slightly worse with arithmetic on WORD-OFFSET, though.

-Nathan