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Date: Fri, 4 May 2001 11:37:27 +0200
From: Xavier Leroy <Xavier.Leroy@inria.fr>
To: Miles Egan <miles@caddr.com>
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] printable digest strings
Message-ID: <20010504113727.A9728@pauillac.inria.fr>
References: <20010503153234.A28259@caddr.com>
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In-Reply-To: <20010503153234.A28259@caddr.com>; from miles@caddr.com on Thu, May 03, 2001 at 03:32:34PM -0700
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> I can't seem to find a function to create printable versions of the
> digest strings generated by the digest module, like the output of
> the common unix md5sum utility.  Am I missing something or does it
> not exist?

It does not exist, but as you said it could be handy.

> If not, it might be a handy addition to the Digest
> module.  At the moment I'm using this fairly gross code of my own:

You can use Printf.sprintf "%02x" to convert each byte to hexadecimal
in a more concise way.  E.g.:

let string_map f s =            
  let rec map_aux res idx =
    if idx < 0 then res else map_aux (f s.[idx] :: res) (idx - 1)  
  in map_aux [] (String.length s - 1)

let hexstring s =
  String.concat "" 
    (string_map (fun c -> Printf.sprintf "%02x" (Char.code c)) s)

Or in a more imperative style (real programmers don't build
intermediate lists :-)

let hexstring s =
  let res = String.create (String.length s * 2) in
  for i = 0 to String.length s - 1 do
    String.blit (Printf.sprintf "%02x" (Char.code s.[i])) 0
                res (2 * i) 2
  done;
  res

Hope this helps,

- Xavier Leroy
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