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I think Vigna's claim is that if you ignore the PractRand tests that fail, it passes. (Really!) The code does explain exactly what the issue is, i.e. that the

I think Vigna's claim is that if you ignore the PractRand tests that fail, it passes. (Really!) The code does explain exactly what the issue is, i.e. that the last bit isn't random: This generator passes the PractRand test suite up to (and included) 16TB, with the exception of binary rank tests, which fail due to the lowest bit being an LFSR; all other bits pass all tests. We suggest to use a sign test to extract a random Boolean value. But I'm tempted to agree this isn't a desirable property for a generic RNG. How many users of JavaScript know about this property? (it's the default RNG for most browser engines) Or does it not matter because they return 53-bit floats?

FabHK 9y ago
In the comment section to the V8 JavaScript blog post [1], Vigna writes: - Technically, it would be better if you used the upper 52 bits, rather than the lower 52 bits, to generate a double. The lowest bit of a xorshift128+ generator is an LSFR, and while people has been happy using LSFR for decades, it is slightly inferior in quality to all other bits. This is really OCD, as computational errors makes the lowest bit almost irrelevant, but now you know. I don't know whether that's been implemented, but the maintainer replied: Thanks for the suggestions! I will definitely revisit the current implementation with your tips in mind. [1] https://v8project.blogspot.nl/2015/12/theres-mathrandom-and-then-theres.html?showComment=1452592903162#c1549004517443909784 https://v8project.blogspot.nl/2015/12/theres-mathrandom-and-...