Need Integer:sqrt in std lib

1

Rust doesn't have an Integer Squareroot function, but needs it.

I raised this issue in Ruby, and they included it in version 2.5 (2.7 was just released Dec 25, 2019).

For large integers, doing something like: (n as f64).sqrt() as usize
will start producing errors above a certain size. This is an inherent limitation of floating point math.

See article here describing problem:

This floating point conversion bug starts to show up early for large 64-bit integers.
This is a necessary fix to implement many numerical algorithms correctly, e.g. in cryptography, which use very large integers.

Discussion in Ruby issue tracker on which implementation to use.

2

I note that integer-sqrt crate implements basically the same algorithm used in Ruby.

https://crates.io/crates/integer-sqrt

3 Likes
3

See this answer in a parallel thread to one of your similar requests.

1 Like
4

Thanks for the heads up.

Part of this process is learning what is part of the std lib and what|where to find external functionality, especially coming from languages (Ruby, Nim) which have these available by default.

I'll check out the crate.

I guess there's a directory of all the crates somewhere, right?

1 Like
5

lib.rs or crates.io. The Rust standard library is small by design.

6

Thanks. I'll start looking there for stuff from now on.

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