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if (n:int) < 0 then (-n) > 0 is FALSE
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Date: -- (:)
From: Pal-Kristian Engstad <pal_engstad@n...>
Subject: if (n:int) < 0 then (-n) > 0 is FALSE
Using OCaml 3.08.3 on the following function:

let pow x n =
  let rec aux x n acc =
    if n == 0 then acc
    else if n == 1 then acc *. x
    else if n land 1 == 0 then aux (x*.x) (n/2) acc
    else aux (x*.x) ((n-1)/2) (x*.acc)
  in
    if n >= 0 then
      aux x n 1.0
    else
      1.0 /. (aux x (-n) 1.0)
;;

I tested this function with

# pow 1.0 (1024 * 1024 * 1024)

To find that it loops forever. The reason is that 1024*1024*1024=2^30 
cannot be represented as a positive number on 32-bit platforms, hence it 
silently converts it to -1073741824, or -2^30. The reason this loops 
again is that -n = -(-20^30) = -20^30......, still negative!

This is obviously a bug - has it since been fixed? But more alarmingly - 
why is there no warning?

Thanks,

PKE.

-- 
Pål-Kristian Engstad (engstad@naughtydog.com), Lead Programmer, ICE
team, Naughty Dog, Inc., 1601 Cloverfield Blvd, 6000 North,
Santa Monica, CA 90404, USA. Ph.: (310) 633-9112.

"Most of us would do well to remember that there is a reason Carmack
is Carmack, and we are not Carmack.",
                       Jonathan Blow, 2/1/2006, GD Algo Mailing List