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My wild ass guess would be one of: a) some high frequency trading algo, b) ray tracing/collision detection in popular game engines, c) the inner loop of google's spider, d) something common to mobile devices (maybe something in wifi or cell service?), or (most likely) e) the bitcoin hash algo.

It makes for an interesting "how many manholes in Manhattan" interview question, and how you could possibly quantify your guesses...

Imagine being the author of those lines of code, if it was possible to figure out :-)

I'd add TCP stack in Linux (kernel). Should be hammered constantly on servers of the world and also gets lots of usage on smartphones and IoT stuff.

Nope. IO would be orders of magnitude less than computation

My money is on Linux's cpu_idle_loop().

Don't forget bitcoin::compute_hash()

I would guess that it is something mobile related. Android?

strcpy, strlen, strchr, memcpy, and their varients

Bitcoin mining?