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by ack_complete 534 days ago
These kinds of tricks are still used today. They're not so useful if you need a reciprocal or square root, since CPUs now have dedicated hardware for that, but it's different if you need a _cube_ root or x^(1/2.4).
1 comments

I wonder to what extent the dedicated hardware is essentially implementing the same steps but at the transistor level.
The big cores do. They essentially pump division through something like an FMA (fused multiply-add) unit, possibly the same unit that is used for multiplication and addition. That's for the Newton-Raphson steps, or Goldschmidt steps.

In hardware it's much easier to do a LUT-based approximation for the initial estimate rather than the subtraction trick, though.

It's common for CPUs to give 6-8 accurate bits in the approximation. x86 gives 13 accurate bits. Back in 1975, the Cray 1 gave 30 (!) accurate bits in the first approximation, and it didn't even have a division instruction (everything about that machine was big and fast).