Tom Lane wrote: > Shachar Shemesh <[EMAIL PROTECTED]> writes: > >> Before you explode at me (again :), I'm not arguing that you can do >> binary based calculations of decimal numbers without having rounding >> errors that come to bite you. I know you can't. What I'm saying is that >> we have two cases to consider. In one of them the above is irrelevant, >> and in the other I'm not so sure it's true. >> > > You're setting up a straw-man argument, though. I was answering your claim that it's impossible to convert decimal to binary based floats without rounding errors. > The real-world problem > cases here are not decimal, they are non-IEEE binary floating > arithmetic. The typical difference from IEEE is slightly different > tradeoffs in number of mantissa bits vs number of exponent bits within a > 32- or 64-bit value. I answered that elsewhere while suggesting a different format that would address that. These numbers do not appear to be a concern in our situation, however. > I seem to recall also that there are machines that > treat the exponent as power-of-16 not power-of-2. I'm pretty sure I don't understand this. Maybe I misunderstood the format, but wouldn't that actually lose you precision with, at most, marginal gain in range? As far as I can see, the moment you no longer work in base 2 you lose the implicit bit, which means you have a one bit less starting point than base 2 notations (all number are denormalized). > So depending on which > way the tradeoffs went, the other format will have either more precision > or more range than IEEE. > Again, should that be a real concern, see my message at http://archives.postgresql.org/pgsql-hackers/2007-05/msg00892.php for details about what the suggestion actually is. Just be sure to read "IEEE" there as meaning "IEEE like". I allowed different sizes for the fields. > regards, tom lane > Shachar

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