Evolving the Go Standard Library with math/rand/v2

&gt; In 2018, Daniel Lemire found an algorithm that avoids the divisions nearly all the time (see also his 2019 blog post). In math&#x2F;rand, adopting Lemire’s algorithm would make Intn(1000) 20-30% faster...<p>I recently found a super simple algorithm that appears to produce a number in the interval [0,N] with a branchless expression with a single multiplication in an extended number size. (Sorry I don&#x27;t have a reference.)<p>Say you want to generate a number, G, in interval [0,N] where N&lt;=UInt32Max. The algorithm is:<p><pre><code> G = uint32( uint64(N)*uint64(rand.UInt32())&gt;&gt;32 ) </code></pre> It seems like this should select a number in the range with no bias. Is there something I missed?

As often I’m impressed by the quality of all of this. The amount of thinking that went into this, this excellent written blog post. I love the Go blog.

I like the Principles section. Very measured and practical approach to releasing new stdlib packages. <a href="https:&#x2F;&#x2F;go.dev&#x2F;blog&#x2F;randv2#principles" rel="nofollow">https:&#x2F;&#x2F;go.dev&#x2F;blog&#x2F;randv2#principles</a><p>The end of the post they mention that an encoding&#x2F;json&#x2F;v2 package is in the works: <a href="https:&#x2F;&#x2F;github.com&#x2F;golang&#x2F;go&#x2F;discussions&#x2F;63397">https:&#x2F;&#x2F;github.com&#x2F;golang&#x2F;go&#x2F;discussions&#x2F;63397</a>

Nice - I wish .NET would be more willing to condemn chunks of the standard library and replace them with something better!

Related, this article discusses difference generators and tradeoffs for Go using them as Source: <a href="https:&#x2F;&#x2F;zephyrtronium.github.io&#x2F;articles&#x2F;randomness.html" rel="nofollow">https:&#x2F;&#x2F;zephyrtronium.github.io&#x2F;articles&#x2F;randomness.html</a>

&gt; Ideally, the v2 package should be able to do everything the v1 package could do, and when v2 is released, the v1 package should be rewritten to be a thin wrapper around v2.<p>And even more ideally, as many v1 usages should be automatically fixed as possible by `go fix` or similar tools. Allowing this to <i>all</i> user packages would be a major improvement over the status quo.

If both are now crypto secure, what&#x27;s the point of having both? Also seems like they&#x27;ve made math&#x2F;rand slower, not a win in my book.