[issue36887] Add integer square root, math.isqrt

[Mark Dickinson]

Mark Dickinson <dickinsm at gmail.com> added the comment:

> I am wondering whether int(sqrt(float(n))) can be used as a good initial approximation.

It can, but I'd prefer to avoid floating-point arithmetic (we don't have any guarantees about the accuracy of sqrt, so you'd always need a check and a fallback for the case where sqrt isn't accurate enough), and there are other purely-integer-based ways to produce a fast initial approximation. I do have some plans to add optimizations, but wanted to get the basic algorithm in first.

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<https://bugs.python.org/issue36887>
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