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Path: utzoo!mnetor!seismo!rutgers!mit-eddie!Holmes.UUCP!pml
From: pml@Holmes.UUCP (Pat Lashley)
Newsgroups: comp.emacs
Subject: blackbox.el
Message-ID: <8706270214.AA08710@Holmes.case.com>
Date: Fri, 26-Jun-87 22:14:33 EDT
Article-I.D.: Holmes.8706270214.AA08710
Posted: Fri Jun 26 22:14:33 1987
Date-Received: Sat, 27-Jun-87 12:34:55 EDT
Sender: uucp@eddie.MIT.EDU
Lines: 47

The following changes to blackbox.el will prevent the placement of
balls outside the board area due to `(random)' returning a negative
number.

diff -c4 blackbox.el~ blackbox.el
*** blackbox.el~        Fri Jun 26 00:33:22 1987
--- blackbox.el Fri Jun 26 18:54:24 1987
***************
*** 51,65 ****
    (setq bb-detour-count 0)
    (bb-insert-board)
    (bb-goto (cons bb-x bb-y)))
  
  (defun bb-init-board (num-balls)
    (random t)
    (let (board pos)
      (while (>= (setq num-balls (1- num-balls)) 0)
        (while
          (progn
!           (setq pos (cons (% (random) 8) (% (random) 8)))
            (bb-member pos board)))
        (setq board (cons pos board)))
      board))
  
--- 51,72 ----
    (setq bb-detour-count 0)
    (bb-insert-board)
    (bb-goto (cons bb-x bb-y)))
  
+ (defun abs-random ()
+   "Return a non-negative random number"
+   (let ((num (random)))
+     (if (< num 0)
+       (- num)
+       num)))
+ 
  (defun bb-init-board (num-balls)
    (random t)
    (let (board pos)
      (while (>= (setq num-balls (1- num-balls)) 0)
        (while
          (progn
!           (setq pos (cons (% (abs-random) 8) (% (abs-random) 8)))
            (bb-member pos board)))
        (setq board (cons pos board)))
      board))