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A calculator that doesn't round

27 points

by dimview

3 days ago

| past

| 8 comments

| constructive-calculator.dimview.org

| HN

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__alexs

3 hours ago

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> 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

2 hours ago

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The 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

The whitepaper was only published in 2005: 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.

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dimview

7 minutes ago

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Thank 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.

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nxobject

2 hours ago

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Well, 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...

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dimview

3 days ago

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Author 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.

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NetMageSCW

2 hours ago

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Maybe you should correct the errors in your post before worrying about the code.

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nomel

2 hours ago

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The 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!

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dimview

20 minutes ago

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This 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.

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bla3

2 hours ago

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> 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.

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B1FF_PSUVM

1 hour ago

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Read. Guy knows what he's doing.

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quixoticelixer-

2 hours ago

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I don't get why this is a big deal. All the calculators I've used have been rectangle.

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jagraff

3 hours ago

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Very 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?

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piinbinary

3 hours ago

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It would also be fun to have a full computer algebra system (like maxima) on a phone

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dimview

15 minutes ago

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That should be doable, too. Maybe as a next project.

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htx80nerd

3 hours ago

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btw 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.

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dimview

24 minutes ago

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Correct, but if you don't know the next digit is 2, you can think it's all 9s, another representation of an integer number.

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Jblx2

3 hours ago

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Edit: Whoops. My bad. This must have been a HN "second chance" winner.

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badc0ffee