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Full Version: HP 35 ROM V2 "exp(ln(2.02) = 2", explanation found
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Hi everybody,
Peter Monta published (Feb 19 2006) the dump of the HP 35 ROM V2 (with bugs):


A month later, I have found the explanation of the flaw in the exponential algorithm "exp(ln(2.02) = 2".
If you are interested in History of Algorithms, please visit my page :

http://www.jacques-laporte.org/HP35 bug.htm

Best regards.
Jacques Laporte
[url:http://www.jacques-laporte.org/HP35 bug.htm]

Nice work.

Note that the HP-35 source code from the Nonpareil package, on which you based the listing on your web site, is Copyright 2004 Eric L. Smith. The copyright notice was unintentionally omitted, which was corrected in later releases of Nonpareil (starting with r120 of the file in the Subversion repository, on 15-Jan-2004). The latest version, r850, can be obtained from ViewVC.

The simulator is GPL'd, so you should make the source code available on your site. Otherwise, to comply with the GPL, you need to accompany the executable (JAR file) with a written offer to provide the source code.

Jacques --

To echo Eric Smith, an impressive effort. Unfortunately for myself, I don't have the requisite background in computer science and assembly to follow it...

Following the links upward, I see that you have developed an entire site containing technical discussions of the HP-35. I'd expect that they are informative...


-- KS

Edited: 16 Mar 2006, 3:07 a.m.

Thank you Eric for you comments.

I must underline that this work could not definitely be possible without your work Nonpareil and P. Monta’s ROM dump.
I couldn’t understand the HP35 ROM instruction by instruction, without the help of your simulator.
My job is reverse engineering not voodoo magic!

All my work is open source minded.
Correction will be made soon to comply with the GPL. For now, I’m going to take a few days off!

Best regards.


Thank you for your kind comments.
I hope my work will help
Best regards,


That's fine, no rush. I see that one of the 35 listings on your site had the copyright notice, and the other (the one you modified?) did not.

I've spent more time studying your site since I posted earlier, and the more I look over it, the more impressed I am. You've done a fantastic job of explaining the algorithms.

The algorithms only changed slightly from the 35 through the early Woodstock series (21/22/25/25C). The first big change to the math routines occurred in the late Woodstock era, in the 67/97, 92, 19C/29C, and maybe the 27. An overview of some of the changes is given in the November 1976 HP Journal article "The New Accuracy: Making 2^3=8" by Dennis Harms.

There were some lesser changes in the 30 series, after which the math code remained fairly stable from that point through the 41 and the Voyager series.

I haven't had time to do any thorough analysis of the differences.

AFAIK, all of the Saturn-based calculators use essentially the same floating-point math routines, derived from the HP-71B. Some of the algorithms used are significantly different from the earlier calculators.



Et merci de vos passionnants articles qui m'ont fait réfléchir et rêver durant les belles années de l'OI -- et je ne parle pas du "catalogue publicitaire" diffusé aujourd'hui!

Bien cordialement




Thank you for your great contributions to "L'OI" newspaper. These articles made me think and dream during many beautiful years.

Friendly yours.


Great Work and highly informative!!! Thanks!

I have found that the links on your pages to Volder, Meggitt and Walther seem to be broken!


Awesome. This is the sort of thread that makes this forum so informative!

Hi and thank you, TomCee.

> I have found that the links on your pages to Volder, Meggitt and Walther seem to be broken!

Yes, sorry ; I've corrected a few of them.
Hope all is ok, now.
best regards.

Hi Etienne,
Thank you very much for the warm words.
I obviously remember myself the beautiful 70's and my first HP35, Altair, TRS80...
My wife could not understand: no furniture in the apartment but so many computers...
One day in 1980, I bought in San Francisco a book by James Farvour, “Microsoft Basic decoded & other mysteries”; the guy commented step by step TRS-80's Rom!
I remember well - it seems so close - that I said to myself : I must do the same for the HP 35!
25 years after, it is almost done.

HP 35 was -and still is- a so brilliant machine!
I personally was using a slide rule when I first put my fingers on it!
That’s why I’m very proud to pay tribute to this monumental breakthrough in computer history.
All the best to you,