[cffi-devel] offer of code contribution - with-array-as-foreign-pointer

[Gustavo]

Hello,

What about CFFI:WITH-POINTER-TO-VECTOR-DATA? Or did you just miss it?
Documentation is missing, but it pines the array within its body (which
means the array won't be moved, but garbage collector might still run) and
grabs the foreign pointer of the array, at least on SBCL.

Regards,
Gustavo.

2010/9/11 JTK <jetmonk at gmail.com>

>
>
> Hello,
>
> I'm using cffi, and I need to perform the common task of passing Lisp
> arrays to foreign code.
>
> This task comes up a lot in scientific code, matrix math, image processing,
> etc.
>
> Normally, it involves a lot of boilerplate to allocate a pointer, copy data
> Lisp  to foreign
> memory, copy the data back, and deallocate the memory.   Getting the
> copying to run
> fast can be tricky.
>
> Hence I wrote a package to automate it.    It maintains a set of
> specialized copying
> functions to copy from array of Lisp type X to foreign memory of type Y.
> On SBCL, copying
> doesn't cons and is reasonably fast (~200 MB a second, there and back)
>
> I've put the package here:
>
>  http://www.megaupload.com/?d=CX1XFMU6
>
> Sorry for the megaupload, and its imposed delay, but I didn't want to spam
> the list with a 100K file.
>
> The package includes a MANUAL.txt and a test package.
>
> I'd be happy to have this included in a user contrib section of CFFI, if
> the maintainers
> think it would be useful.
>
>
>
>
> Here's an example the main macro does:
>
>
>  (LET ((U (MAKE-ARRAY 100 :ELEMENT-TYPE 'SINGLE-FLOAT :INITIAL-ELEMENT
> 1.0)))
>    ;;
>    (WITH-ARRAY-AS-FOREIGN-POINTER
>           (U PU :FLOAT              ;; LISP-VAR    POINTER-VAR
>  CFFI-FOREIGN-TYPE
>           :LISP-TYPE SINGLE-FLOAT   ;; promise U is a single-float array
>           :START 2                  ;; begin at index 2 of of Lisp array
>           :END   7                  ;; last index used is 6
>           :COPY-TO-FOREIGN   T      ;; put contents of Lisp into foreign
> memory
>           :COPY-FROM-FOREIGN T)     ;; copy back from FFI space to lisp
> array
>         ;;
>         ;; at this point, PU is a foreign pointer containing data copied
>         ;; from the array starting at element 1 and ending at 6, of type
> :FLOAT.
>
>         (SOME-FOREIGN-FUNCTION PU))
>       ;;
>       ;; at end, all foreign memory is deallocated, and U has been copied
>       ;; back from foreign space, but the 0th element of U is untouched
>       ;; because START was 1, not 0
>     )
>
>
> -John
> _______________________________________________
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>
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