[corsix]

AArch64 NEON has the URSQRTE instruction, which gets closer to the OP's question than you might think; view a 32-bit value as a fixed-precision integer with 32 fractional bits (so the representable range is evenly spaced 0 through 1-ε, where ε=2^-32), then URSQRTE computes the approximate inverse square root, halves it, then clamps it to the range 0 through 1-ε. Fixed-precision integers aren't quite integers, and approximate inverse square root isn't quite square root, but it might get you somewhere close.

The related FRSQRTE instruction is much more conventional, operating on 32-bit floats, again giving approximate inverse square root.

[voidbert]

What task benefits from using such a complex instruction so easily dividable in simpler ones for it to be present in aarch64?

[colechristensen]

Inverse square root is for normalizing vectors particularly in computer graphics calculations, it needs to be run a whole lot very fast.

https://en.m.wikipedia.org/wiki/Fast_inverse_square_root#Mot...

[nanidin]

Neon is SIMD so I would presume these instructions let you vectorize those calculations and do them in parallel on a lot of data more efficiently than if you broke it down into simpler operations and did them one by one.