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From: madler@piglet.caltech.edu (Mark Adler)
Newsgroups: comp.sys.handhelds
Subject: Re: HP48 thinks -3 in binary is zero!
Message-ID: <1990Jul2.203602.13767@laguna.ccsf.caltech.edu>
Date: 2 Jul 90 20:36:02 GMT
References: <576@cbnewsb.ATT.COM>
Sender: news@laguna.ccsf.caltech.edu
Organization: California Institute of Technology, Pasadena
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>> Upon further inquiry, it turns out that << -3 R->B >>  produces #0h.

I think this is documented.  Unlike the HP-16C, the HP-48SX (and it's
ancestors, the 28C and 28S) don't believe in negative binary numbers.
If you're below the range of non-negative integers allowed by the
current wordsize, you get zero from R->B, and if you're above, you get
the word filled with binary one's (i.e. FFFFh if the wordsize is 16).

It wouldn't be a big deal, nor largely inconsistent if it did convert
negative numbers properly, but it doesn't.  The fix is simply to convert
the positive number and negate it.  For example, this program converts
positives or negatives to binary like one would want it to:

<< DUP ABS R->B SWAP IF 0 > THEN NEG END >>

Mark Adler
madler@tybalt.caltech.edu