[FabHK]

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-...