Re: [Caml-list] int -> byte array (and back)

[Issac Trotts <ijtrotts@nez-perce.inria.fr>]

On Wed, Nov 19, 2003 at 12:31:23PM -0800, Dustin Sallings wrote:
> 
> 	I need to be able to get a byte array (specifically in little-endian 
> format) from an int.  I'll need the reverse as well.  Is there anything 
> that does that in the distribution, or do I need to calculate it 
> myself?  Just trying to do things the right way.

Here's a way to do it:

# open Bigarray;;
# #load "bigarray.cma";;
# let i=Random.int 1024;;
val i : int = 735
# let a_of_i i =
   let a=Array1.create int8_unsigned c_layout 4 in
   a.{0} <- i land 0xff;
   a.{1} <- (i lsr 8) land 0xff;
   a.{2} <- (i lsr 16) land 0xff;
   a.{3} <- (i lsr 24) land 0xff;
   a;;
val a_of_i :
  int ->
  (int, Bigarray.int8_unsigned_elt, Bigarray.c_layout) Bigarray.Array1.t =
  <fun>
# let i_of_a a =
   a.{0} lor (a.{1} lsl 8) lor (a.{2} lsl 16) lor (a.{3} lsl 24);;
val i_of_a : (int, 'a, 'b) Bigarray.Array1.t -> int = <fun>
# let a = a_of_i i;;
val a :
  (int, Bigarray.int8_unsigned_elt, Bigarray.c_layout) Bigarray.Array1.t =
  <abstr>
# a.{0},a.{1},a.{2},a.{3};;
- : int * int * int * int = (223, 2, 0, 0)
# i_of_a a;;
- : int = 735

-- 
Issac Trotts
Programmer
Center for Neuroscience
University of California, Davis 

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