Carmack didn't invent it either, my physics teacher was saying that a lot 17 years ago so it's clearly a common thing.

a possible source is in the replies to that tweet: https://twitter.com/RobbieBC/status/419324772754132992

Honestly it wouldn't surprise me if it had been invented multiple times independently, it's just too obvious to anyone that has had to deal with calculation.

(But thanks for sharing what us without a Twitter account cannot see otherwise anymore…)

Clearly we must now start referring to it as ‘Carmack’s sign error joke’ ;)

had you not mentioned that, we might have gotten another fast inverse square root origin investigation

fast (multiplicative) inverse square root.

autocorrect or dyslexia. whoever wins, i lose

It was common saying 30 years ago when we were preparing for IT Olympiads in Eastern Europe - if you do even number of errors chances are your program will work ok.