URGENT: BUG-FIX (and heavy optimization of prime-related functions)

[kckennylau]

No description provided.

[codecov-io]

Current coverage is 85.96% (diff: 44.64%)

Merging #67 into master will decrease coverage by 1.83%

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[kckennylau]

DO NOT MERGE YET
there is still bugs

[kckennylau]

In the future could you please write more tests?

[kckennylau]

Passed my tests.

[Mego]

Why on earth did you write a custom isqrt function? Surely int(n**.5+1) would be much faster.

[kckennylau]

I was worried about floating point inaccuracies... also, I believe sqrt(n) would be faster than n**.5. I do not believe that it would be "much faster" though, since the complexity of my isqrt function is still linear.

[kckennylau]

And I do not think that this is a matter more urgent than the bugfix?

[Mego]

I'll merge it, but I'm changing it back to math.sqrt. The native C code for the math library will certainly be faster than the Python code.