[request] efficient way to copy from bytevectors to malloc()ed memory

[Andreas Rottmann]

It would be nice to have a fast way to move data from Scheme
bytevectors to C-accessible memory and vice-versa. I've attached a
patch that adds a procedure called `memcpy' to the FFI that does
this.

In a simple synthetic benchmark, the speed gain ranges from a factor
of ~3 (copying 8 bytes) to a factor of ~240 (copying 64KiB); compared
against a naive Scheme implementation of memcpy using byte operations
on bytevectors and FFI pointers.

In a quasi-real-live scenario (a webserver implemented using
libsoup[0] via the FFI), just switching to the attached implementation
of memcpy instead of using the naive one implemented in Scheme doubled
the throughput in case of serving a 50KiB static file.

[0] http://live.gnome.org/LibSoup

[Abdulaziz Ghuloum (aghuloum)]

Looks good. Patched in revision 1771. Thanks.

[Derick Eddington (derick-eddington)]

A couple typos:

=== modified file 'scheme/ikarus.pointers.ss'
--- scheme/ikarus.pointers.ss 2009-04-30 09:35:49 +0000
+++ scheme/ikarus.pointers.ss 2009-05-01 05:02:52 +0000
@@ -127,7 +127,7 @@
     (unless (and (fixnum? src-offset) (fx>=? src-offset 0))
       (die who "not a positive fixnum" src-offset))
     (unless (and (fixnum? count) (fx>=? count 0))
- (die who "not a postive fixnum" count))
+ (die who "not a positive fixnum" count))
     (cond ((and (pointer? dst) (bytevector? src))
            (unless (fx<=? (fx+ src-offset count) (bytevector-length src))
              (die who "source bytevector length exceeded"
@@ -142,7 +142,7 @@
                          dst dst-offset (pointer+ src src-offset) count))
           (else
            (die who "destination and source not a bytevector/pointer pair"
- dst dst))))
+ dst src))))

   ;;; getters and setters