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A comment on Revisiting the Fast Inverse Square Root – Is It Still Useful?. Parent comment

Re:Revisiting the Fast Inverse Square Root – Is It Still Use... by pclmulqdq on Thursday April 20, 2023 @10:40PM (#35649199)
If you're doing ~20 other FP ops (not including division) per inverse square root and not using a huge dependency chain of inverse square roots, you might not even notice the impact of using an exact inverse square root with this method.

Short of functions like exp and the trig functions, DIY approximations are usually not worth it these days.

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Re:Revisiting the Fast Inverse Square Root – Is It Still Use... by adgjlsfhk1 on Friday April 21, 2023 @12:56AM (#35649946)
polynomials are still king. a 6th degree polynomial is often enough and will be faster than a 2nd degree rational.
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Re:Revisiting the Fast Inverse Square Root – Is It Still Use... by pclmulqdq on Friday April 21, 2023 @07:46AM (#35652366)
A 6th degree polynomial is firmly in the "fast approximation" category. I think sin/cos are ~15th degree polynomials for 1 ULP of precision.
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Re:Revisiting the Fast Inverse Square Root – Is It Still Use... by moonchild on Friday April 21, 2023 @08:00AM (#35652459)
https://github.com/rutgers-apl/The-RLIBM-Project/blob/main/l... has a lot less and claims to be correctly rounded.
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Re:Revisiting the Fast Inverse Square Root – Is It Still Use... by pclmulqdq on Friday April 21, 2023 @08:12AM (#35652558)
For 32-bit float, yes. For double precision, not so much.
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Re:Revisiting the Fast Inverse Square Root – Is It Still Use... by adgjlsfhk1 on Friday April 21, 2023 @01:09PM (#35656858)
sin/cos commonly use 2 different 5th degree polynomials (depending on quadrant of the sin graph) https://github.com/JuliaLang/julia/blob/bb83df1d61fb649efd15...
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