Re: List and String concatenation speed.

Many thanks!
I use

let
    val arr = Primitive.Array.arrayUnsafe (a_length + b_length)
in
    string_concat_memmove(arr, a, a_length, b, b_length);
    Primitive.String8.idFromWord8Vector (Primitive.Vector.fromArrayUnsafe
arr)
end

and got 20 times performance boost!

Nick.

2016-08-30 16:57 GMT+03:00 Matthew Fluet <[email protected]>:

> No, that wouldn't be any faster; in fact, you've added a bit of overhead.
>
> The `Word8Array.array` needs to initialize the array, by writing 0w0
> element by element into the array.  Then there is a little bit of FFI
> overhead.  Then the `Byte.bytesToString` converts a mutable array to
> an immutable vector, by copying element by element.
>
> Within the Basis Library implementation, we are able to use unsafe
> features.  In particular, we are able to create an uninitialized array
> to receive the elements and then we are able to perform a cast from
> the array to vector.  We can consider adding a memmove like primitive
> to improve these kinds of operations, but it would almost certainly
> need to be within the compiler/Basis Library.
>
> On Tue, Aug 30, 2016 at 9:07 AM, Kostirya <[email protected]> wrote:
> > Hello.
> > I've decided to use FFI for String.^.
> > However, the speed has not been increased (slowed down, in fact).
> > The code is lower. I think I've done everything properly?
> >
> > C:
> >
> > #include <sys/types.h>
> > #include <string.h>
> >
> > void string_concat_memmove(void *dst, const void *src1, size_t len1,
> const
> > void *src2, size_t len2) {
> >     memmove(dst, src1, len1);
> >     dst += len1;
> >     memmove(dst, src2, len2);
> >     return;
> > }
> >
> >
> > SML:
> >
> >     val string_concat_memmove = _import "string_concat_memmove" :
> Word8.word
> > array * string * int * string * int -> unit;
> >
> >     fun op ^ (a: string, b: string): string =
> >         let
> >             val a_length = String.size a
> >             and b_length = String.size b
> >         in
> >             if a_length = 0 then b else
> >             if b_length = 0 then a else
> >             let
> >                 val arr = Word8Array.array(a_length + b_length, 0w0)
> >             in
> >                 string_concat_memmove(arr, a, a_length, b, b_length);
> >                 Byte.bytesToString (Word8Array.vector arr)
> >             end
> >         end
> >
> > Best Regards.
> > Nick.
> >
> > 2016-08-29 16:46 GMT+03:00 Kostirya <[email protected]>:
> >>
> >> Yes. Poly/ML use memmove to to implement String.^
> >>
> >>
> >> 2016-08-29 16:21 GMT+03:00 Matthew Fluet <[email protected]>:
> >>>
> >>> >> poly --script string_concat.sml
> >>> > 0.462269
> >>> >
> >>> >> mlton string_concat.sml && ./string_concat
> >>> > 2.713323
> >>>
> >>> It looks like Poly/ML uses memmove to implement String.^, which would
> >>> be more efficient for character sequences.
> >>
> >>
> >
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