Implement sqrt for BigInt and BigUint #51
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This commit adds sqrt method for calculating square root of a non-negative integer to BigInt and BigUint types. Square root is obtained via Newton's method with a good initial guess to improve performance. Tests and benchmark were also added. Signed-off-by: Manca Bizjak <manca.bizjak@xlab.si>
Ah, sorry, I didn't update the benchmarks for the new |
src/biguint.rs
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| loop { | ||
| s = u; | ||
| let q = self.div_floor(&s); | ||
| let t: BigUint = &s + &q; |
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We don't need q after this, so adding &s + q by value will let it reuse that memory allocation.
src/biguint.rs
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| let t: BigUint = &s + &q; | ||
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| // Compute the candidate value for next iteration | ||
| u = t.div_floor(&two); |
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Any reason you're using div_floor instead of the / operator? With the operator you can also use integer literals, like t / 2u32. But even more, t >> 1 is probably faster.
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No reason whatsoever, it just slipped my mind it seems. I replaced the usage of div_floor with the / and >> operators as appropriate, and also replaced the lsh call with <<. Looks much cleaner now.
This commit cleans up implementation of the sqrt method on the BigUint type. Method calls of div_floor and lsh were also replaced with overloaded operators. Signed-off-by: Manca Bizjak <manca.bizjak@xlab.si>
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So, I've add a new |
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Great, I'd be happy to. I already have a draft for the |
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Closing in favor of #56. |
56: Implement Roots for BigInt and BigUint r=cuviper a=mancabizjak Supersedes #51 . Since there is now a `Roots` trait with `sqrt`, `cbrt` and `nth_root` methods in the `num-integer` crate, this PR implements it for `BigInt` and `BigUint` types. I also added inherent methods on both types to allow the users access to all these functions without having to import `Roots`. PS: `nth_root` currently uses `num_traits::pow`. Should we perhaps wait for #54 to get merged, and then replace the call to use the new `pow::Pow` implementation on `BigUint`? Co-authored-by: Manca Bizjak <manca.bizjak@xlab.si>
Related to #3.
I needed to calculate square root of a big integer in the project I'm working on, so I thought maybe this can be useful to others as well.
This PR adds
sqrt()method for calculating square root of a non-negative integer toBigIntandBigUinttypes. Square root is obtained via Newton's method, with a reasonable initial guess to improve performance.Benchmark is included, although I had to replace the implementation of
StdRngwithThreadRngin order to be able to run it.