Re: float conversion / presentation problem ?

On Thu, Apr 07, 2005 at 01:02:50AM -0400, Tom Lane wrote:
> John R Pierce <pierce@hogranch.com> writes:
> > Tom Lane wrote:
> >> You do realize that float4/real is only good to six decimal
> >> places on most platforms?
>
> > and importantly, are stored as binary fractions.  0.10000 decimal
> > is a repeating fraction in binary, its like .1100110011.... x 2^-2
> > or something as a FLOAT.
>
> Right, and conversely a fraction that's cut off at a certain number
> of base-2 digits often corresponds to a repeating pattern of base-10
> digits.  I once had a clue about the exact laws for this, but it was
> many years ago :-(

As with base-10, any denominator that can't be expressed as a power of
the prime factors in the base results in a repeating number.  So
basically any denominator that can't be expressed as 2^n turns into a
repeating binary doohicky.

Cheers,
D
--
David Fetter david@fetter.org http://fetter.org/
phone: +1 510 893 6100   mobile: +1 415 235 3778

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