Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!willett!ForthNet
From: ForthNet@willett.UUCP (ForthNet articles from GEnie)
Newsgroups: comp.lang.forth
Subject: PUZZLES AND PROBLEMS
Message-ID: <1384.UUL1.3#5129@willett.UUCP>
Date: 25 Jul 90 03:01:30 GMT
Organization: String, Scotch tape, and Paperclips.  (in Pgh, PA)
Lines: 33

Category 3,  Topic 35
Message 127       Mon Jul 23, 1990
W.BADEN1 [Wil]               at 21:25 PDT
 
Roger Bicknell writes,
 rb> No No No, he said - you definitely require a Loop! I said - Na - 

Strictly speaking you win because he said "definitely" and any loop with a
constant number of iterations can be unrolled.  Here is a 16-bit version.

: lg ( i -- log2 i)
   2/    DUP IF    EXIT    THEN
   2/    DUP IF    DROP 1    EXIT    THEN
   2/    DUP IF    DROP 2    EXIT    THEN
   ... and so on ... 
   DROP 15 ;

If there's any money riding on this, you collect.  But I'm sure the three of
us agree that this isn't what he meant.

The problem you're thinking of is to test for a number's being a power of 2:

: powerOf2? ( n -- flag) DUP 1- AND    0= ;

Or if you don't want 0 to be a power of two:

: powerOf2? ( n -- flag) DUP IF    DUP 1- AND    0= ( flag) THEN ;

Procedamus in pace.

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