How hard can generating 1024-bit primes really be?
How hard can generating 1024-bit primes really be?
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11 comments
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Nice article, I enjoyed it. Why float sqrt has been used? Integer sqrt is way faster and easily supports integers of any lengths
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The builtin
u64.isqrtseems to be available in nightly only, and additionally I guess the author didn't want to use any external crates as part of their self-imposed challenge. Though I think there may be an off-by-one result withf64.sqrtI don't think this functionally breaks their u64 code because they loop toroot_n + 1.https://doc.rust-lang.org/std/primitive.u64.html#method.isqrt
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Algorithm is so plain and simple, it doesn’t require nightly or Rust specifically to implement.
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Well, yeah, but you asked why they didn't use integer sqrt. It's something many programming languages just don't have. Or if they do, it's internally implemented as a sqrt(f64) anyway, like C++ does.
Most CPUs AFAIK don't have integer sqrt instructions so you either do it manually in some kind of loop, or you use floating point...
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Integer sqrt is usually not a library function and it’s very easy to implement, just a few lines of code. Algorithm is well defined on Wikipedia you read a lot. And yes, it doesn’t use FPU at all and it’s quite fast even on i8086.
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I doubt doing it in software like that outperforms sqrtss/sqrtsd. Modern CPUs can do the conversions and the floating point sqrt in approximately 20-30 cycles total. That's comparable to one integer division. But I wouldn't mind being proven wrong.
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Integer sqrt can be used for integers with any length, not only for integers fit into f64
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11 comments