4 ms·
A calculator that doesn't round
- dimview 4mo agoAuthor here. I could not find a constructive‑reals calculator on iPhone, so I ported the engine Android uses: Hans Boehm's com.hp.creals plus AOSP's UnifiedReal/BoundedRational. Used Opus 4.8 to do the port and Fable 5 for the review. Fable 5 caught a couple of real concurrency bugs the port introduced while adapting Java's synchronized/AsyncTask to Swift concurrency, including one that was a memory‑safety bug on shared singletons like π, not just a wrong digit. None would have shown up in the unit tests. Writeup has the details. It's an early iPhone TestFlight beta (link in the post); happy to go deep on either the constructive‑reals side or the AI‑assisted‑dev side.
- nomel 4mo agoThe old HP calculators, and their emulators, have a computer algebra system, for symbolic maths, that supported this. The user interfaces leave much to be desired, but some also have reverse Polish notation!
- dimview 4mo agoThis is different from a CAS. For example, if you ask it to do exp(100)+1-exp(100), it does not rearrange and cancel out the two exp(100)s. Instead, it does exp, addition, and subtraction, all with as many digits as you ask for.
- nomel 4mo agoSure. I was speaking to the what, not how. > that doesn’t round at all. It computes with constructive real numbers: every result is exact, and you can scroll any answer for as many correct digits as you want. A CAS is a practical way to achieve this, where everything is stored symbolically, with no rounding, until final calculation. Unlimited precision was through Erable [1]. This was included with/as HP49 CAS, but was an add-on with HP48. Many HP48 are on the iOS app store. The one I tried about a decade ago had the add-on, and I see many still there (but not sure if they have the add-on). The "S" in CAS is "system", so it's a bit open. [1] https://en.wikipedia.org/wiki/Erable https://en.wikipedia.org/wiki/Erable
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- NetMageSCW 4mo agoMaybe you should correct the errors in your post before worrying about the code.
- dimview 4mo agoCorrected the dates, thank you! What are the other errors?
- jagraff 4mo agoVery interesting, thank you for posting! I'm curious - roughly how many tokens do you think you used during the initial port and subsequent bug hunting and fixes?
- dimview 4mo agoFor Opus 4.8, 142.3k input, 2.0m output for the entire project. No longer have access to Fable 5 to check.
- piinbinary 4mo agoIt would also be fun to have a full computer algebra system (like maxima) on a phone
- Jblx2 4mo agoEdit: Whoops. My bad. This must have been a HN "second chance" winner.
- ColinWright 4mo agoEr, that's this submission.
- badc0ffee 4mo agoThat looks like a link right back to this thread?
- deleted 4mo ago[deleted]
- htx80nerd 4mo agobtw if you turn the iphone calc into landscape mode and switch you scientific calc it does Ramanujan's constant without rounding, but stops after the twelve 9s.
- dimview 4mo agoCorrect, but if you don't know the next digit is 2, you can think it's all 9s, another representation of an integer number.
- __alexs 4mo ago> Hans Boehm built a Java library for this in the 1980s and 90s Hans is such a prolific programmer that he wrote a Java library before Java was even invented?
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- tomjakubowski 4mo agoThe article has so many of the hallmarks of LLM writing, naturally it will have some hallucinated factoids too. "What that gives you: [bullet list]", "What got ported: [bullet list]", "foo: x, y, just z" Boehm's Java library has copyright dates of 1999 and 2001-2004. https://www.hboehm.info/new_crcalc/CR.java https://www.hboehm.info/new_crcalc/CR.java The whitepaper was only published in 2005: https://www.sciencedirect.com/science/article/pii/S1567832604000736 https://www.sciencedirect.com/science/article/pii/S156783260... I have a dimview now of the blog, and of this Swift port of the library, indeed.
- dimview 4mo agoThank you. Of course the dates were out of order. The Java library (com.hp.creals) is 1999-2004, paper is from 2005. Unfortunate price of LLM-assisted development. Corrected.
- nxobject 4mo agoWell, you know, you go into your Smalltalk-80 workstation for a hack sesh, and an all-nighter later you end up with an implementatkon of Swing...
- quixoticelixer- 4mo agoI don't get why this is a big deal. All the calculators I've used have been rectangle.
- bla3 4mo ago> I built one, by porting Boehm’s engine. > It’s 2026, so I didn’t hand-write the port. I directed Opus 4.8 to translate the source line by line into Swift I wish I could filter out stuff like this. Cool work by Hans Boehm, but what's the value add in this blog post.
- B1FF_PSUVM 4mo agoRead. Guy knows what he's doing.
- IAmBroom 4mo agoYou mean his AI wrote something you like... which is factually incorrect, so it's basically fanfic.