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Comment by Retr0id | Hacker News Reader

This was my first thought too, and they cover it in more detail here https://fingerprint.com/blog/audio-fingerprinting/#why-the-a...

TL;DR different codepaths even within the same codebase (e.g. SIMD variants) can result in subtly different floating point results (iiuc, likely related to to the fact that floating point math is unexpectedly sensitive to order of operations etc.)

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Funny how when I posted more or less exactly this comment in another context recently a lot of people refused to take me seriously!

https://news.ycombinator.com/context?id=39633730

Floats are deterministic, though (if they weren't, this wouldn't be a workable fingerprinting vector). Reordering of operations (etc.) in a way that would actually change the results needs to be done by human edits, or with compiler options like ffast-math that explicitly allow the compiler to "break the rules" and make such changes. In either case, the concrete instructions emitted by the compiler will have deterministic behavior (and if they don't, that's a hardware bug)

What word would you use if sin(x) returns a different value on different platforms, or even different OS or librsry version? Sure smells like a fiction that depends on external state rather than simply its input.

The existence of platforms that do not conform to their own specifications does not make an operator non-deterministic.

Edit: I found this pretty great article on the subject https://randomascii.wordpress.com/2013/07/16/floating-point-...

We're both right, depending on how you frame the question.

sin(x) is platform-dependent.

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