Mmastodon TechnologySoftware first seen 7 h ago, last 5 h ago, peak #10

Mysterious 'what the...?' code comment left in shipped source

Original: The comment in the original code says "what the ...?", and it was left in the shipped source. Noone who found this file

A source file shipped with an unexplained constant and a profane comment reading "what the...?" is drawing attention among programmers. The story being shared: no one reviewing the file could explain the value, someone eventually derived the better constant but never documented the method. The constant relates to a Newton-Raphson iteration that lands within 0.175% of the correct result after one step, echoing the famous fast inverse square root trick.

Why now: Programmers are amused by undocumented magic constants in shipped code, a familiar phenomenon popularised by Quake's fast inverse square root.

Newton-Raphson methodfast inverse square root

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Evidence

• The comment in the original code says "what the ...?", and it was left in the shipped source. Noone who found this file could explain the constant. Somebody searched for the better one, found it, and never wrote down how. One step of Newton-Raphson after it lands within 0.175%,… · justbits · 4

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