On Tue, 9 Oct 2007 14:56:37 +0100, Jon Harrop wrote

> In this context, yes. In general, strings are not as efficient as 
> the equivalent concrete data structure in C. Specifically, using 
> strings as a byte array and applying arithmetic operations to the 
> elements is significantly slower in OCaml than C.
> 
> The only option you have in OCaml is to blow your memory wad and use 
> an int array, which is fast but wastes enormous amounts of space and 
> still has different modulo-arithmetic properties (you might want 8-
> bit for some apps). Consequently, OCaml is not very good for 
> arithmetic operations over byte arrays.

I'd moaned about this a few years ago, and Xavier pointed out the following:

"A better alternative is to declare

external get_byte: string -> int -> int = "%string_safe_get"
external set_byte: string -> int -> int -> unit = "%string_safe_set"

and use these two functions to access strings as if they were byte
arrays.  set_byte will store the low 8 bits of its third argument, so
you'd save on "land 0xFF" operations too."

It works pretty well for getting and setting bytes of a string.  There's 
also the int8_* bigarrays, but I've not used them much, so I can't say if 
they're of much help, but they certainly weren't horrible.

--

William D. Neumann