Binary file I/O

Binary file I/O

[John Whitley]

I am about to implement a wavelet-based audio compression algorithm,
part of my Ph.D. research, in OCaml.  To this end, I must read and
write binary data streams representing the input digital audio and the
output compressed audio stream.

Is there a standard way of handling binary file I/O in OCaml, or must
I resort to handling input and output bitstream formatting in C?

Thanks,
John Whitley

Re: Binary file I/O

[Pierre Weis]

> Is there a standard way of handling binary file I/O in OCaml, or must
> I resort to handling input and output bitstream formatting in C?
> 
> Thanks,
> John Whitley

The standard way to input and output binary files in Caml is to use
the bin versions of the channel opening primitives open_in and
open_out, namely open_in_bin and open_out_bin (those primitives
prevent the interpretation and convertion of end-of-line
characters). Then you read/write the channel as usual, either one
character at a time using input_char/output_char or directly via a
string buffer of your own using the input/output primitives. Direct
handling of binary integers is also available using
input_binary_int/output_binary_int.

In any case, you may access to the bits of your bitstream by first
accessing the characters and then applying the usual mask and shift
stuff (lnot) (land) (lor) (lsr) (lsl).

For easier handling of these operations you may define associated
infix symbols, for instance, trying to be (loosely) reminiscent of C
syntax:

let ( << ) = (lsl)
and ( >> ) = (lsr)
and ( &! ) = (land)
and ( |! ) = (lor)
and ( ~! ) = (lnot);;

Then proceed as usual, for instance

let nth_bit n j = (n &! (0x1 << j)) >> j;;

let nth_bit_char c j = nth_bit (Char.code c) j;;

Best regards,

Pierre Weis

INRIA, Projet Cristal, Pierre.Weis@inria.fr, http://cristal.inria.fr/~weis/