The algorithm used in DivSqrtRecF64_mulAddZ31 to calculate square-root

[zk000888]

What is the algorithm used to calculate square-root in DivSqrtRecF64_mulAddZ31.scala? Dose it use Goldschmidt or Newton-Raphson algorithm, and can you provide some references about the algorithm it used?
Thank you.

[DecodeTheEncoded]

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