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

[Gustavo]

Actually, there is documentation, it's linked in CFFI's main page:

http://common-lisp.net/gitweb?p=projects/cffi/cffi.git;a=blob_plain;f=doc/shareable-vectors.txt

<http://common-lisp.net/gitweb?p=projects/cffi/cffi.git;a=blob_plain;f=doc/shareable-vectors.txt>You
seem to need to use CFFI:MAKE-SHAREABLE-BYTE-VECTOR to create the array.

Em 12 de setembro de 2010 20:39, Gustavo <gugamilare at gmail.com> escreveu:

> 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
>> _______________________________________________
>> cffi-devel mailing list
>> cffi-devel at common-lisp.net
>> http://common-lisp.net/cgi-bin/mailman/listinfo/cffi-devel
>>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mailman.common-lisp.net/pipermail/cffi-devel/attachments/20100912/1f703d8b/attachment.html>