Re: [Caml-list] String, Array, Bigarray.char

[Markus Mottl <markus.mottl@gmail.com>]

On Thu, May 9, 2013 at 9:32 AM, Tom Ridge
<tom.j.ridge+caml@googlemail.com> wrote:
> This presumably takes O(n) time (where n is the length of the string
> bs). My question is: is there functionality to move values between
> these types at cost O(1)? Basically, I'm hoping that String is
> implemented as A.of_array Bigarray.char Bigarray.c_layout or
> similar...

This is unfortunately impossible, because OCaml-strings live in the
OCaml-heap, whereas the contents of bigstrings (i.e. bigarrays of
chars) live in the C-heap.

The Jane Street Core library has a Bigstring module in
Core.Std.Bigstring, which builds on bigarrays of the same type that
you are using here.  This Bigstring-module also features functions for
converting and blitting ordinary OCaml strings to bigstrings.  The
"workhorse" function for that purpose is written in C and uses memcpy,
which is as fast as one could hope for.  It also supports all
functions that the standard String-module offers so you shouldn't have
to convert back and forth between strings and bigstrings in the first
place.

Regards,
Markus

--
Markus Mottl        http://www.ocaml.info        markus.mottl@gmail.com