On Thu, Apr 07, 2005 at 01:02:50AM -0400, Tom Lane wrote: > John R Pierce <[EMAIL PROTECTED]> 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 [EMAIL PROTECTED] http://fetter.org/ phone: +1 510 893 6100 mobile: +1 415 235 3778 Remember to vote! ---------------------------(end of broadcast)--------------------------- TIP 5: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
