and you know that the "real" value is somewhere between +/- 1 ULP (actually, I think +/- 0.5 ULP, really) from the value stored in the 64-bit double float

Thanks for elaborating.
If these considerations are relevant to the post that started this thread, I'm genuinely curious to know just what that relevance is ... because I'm not really seeing it, and I'd hate to be missing out on something ;-)
(If they're not relevant, then that's OK. I always find thinking about and fiddling with such considerations to be fun, anyway.)

The doubles 0.5, 0.3, and 0.1 all have ULPs of the same value (2 ** -53) - yet they all differ from their respective rational representations (5/10, 3/10, 1/10) by different amounts.
It seems to me that the (details of the) behaviour reported by the OP has more to do with the size of the rounding error, than with the value of the ULP.

I'll check out Machine::Epsilon and Data::IEEE754::Tools.

Cheers,
Rob

In reply to Re^6: what did I just see..? by syphilis
in thread what did I just see..? by ishaybas

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