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Exact integer-valued floats

Paul Rubin no.email at nospam.invalid
Fri Sep 21 18:23:41 EDT 2012 
Steven D'Aprano <steve+comp.lang.python at pearwood.info> writes:
> Have I got this right? Is there a way to work out the gap between one 
> float and the next?

Yes, 53-bit mantissa as people have mentioned.  That tells you what ints
can be exactly represented.  But, arithmetic in some situations can have
a 1-ulp error.  So I wonder if it's possible that if n is large enough,
you might have something like n+1==n even if the integers n and n+1 have
distinct floating point representations.
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