Re: [Ocaml-lib-devel] write_double

[Janne H. <jjh...@gm...>]

> > Is it possible to match the speed-ups using pure OCaml code?  eg.  by
> > carefully looking at the generated assembler (ocamlopt -S) and
> > studying why it might be slow?
>
> yes I have read the gas code of the extlib version compared to the one of
> the
> mixed ocaml/C, and even without this just reading the original code it is
> easy to understand what makes the difference:


If IO module is used to write out to a file, it would sound like the
overhead of writing to output would far outweigh benefits of tighter
assembly code for writing out doubles.  Wouldn't calling write_byte eight
times be much more expensive than the few shift instructions?

It looks like your C/Ocaml implementation with the ocaml-side string is not
thread safe?  Perhaps this doesn't happen with the current OCaml run-time,
but it looks like if two threads would enter double_cast at the same time,
you'd corrupt buf_str?

let buf_str = "01234567"
external double_cast: buf_str:string -> float -> unit = "double_cast"

Janne