Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!brutus.cs.uiuc.edu!apple!dan
From: dan@Apple.COM (Dan Allen)
Newsgroups: comp.sys.handhelds
Subject: HP-48SX BYTES Function
Keywords: HP-48SX, calculators, portable computers, handhelds, HP
Message-ID: <39410@apple.Apple.COM>
Date: 12 Mar 90 03:52:22 GMT
Distribution: comp.sys.handhelds
Organization: Apple Computer Inc, Cupertino, CA
Lines: 18

The HP-48SX has a neat function that returns the amount of memory any
object occupies, as well as a binary checksum.  This BYTES function
seems to do a good job of hashing objects.  Does anyone know the details
of the internal checksumming routine?

Note: the numbers -9 through 9 checksum to zero, as they are 2.5 byte
objects (pointers to these frequently used numbers in ROM), whereas
other numbers are 10.5 bytes and have a very well scattered range of
checksums.

Note #2: the checksum operation is VERY fast compared to any comparable
checksumming operations that I have written.

Conjecture #1: if you need to create a hash table on the HP-48, using
BYTES as your hash function would be the way to go.  Any comments?

Dan Allen
Apple Computer