On Fri, Nov 13, 2009 at 03:07:27AM +0000, Simon Slavin wrote: > > On 13 Nov 2009, at 12:34am, Nicolas Williams wrote: > > > On Thu, Nov 12, 2009 at 11:40:23PM +0000, Simon Slavin wrote: > >> There's still some possibility for confusion, however: how many places > >> of decimals do you use for each currency ? As far as I know, no > >> currently traded currency uses more than two digits of precision. > > ^^^^^^^^^^^^^^^^^^^^^^^ > > They use integer math to avoid floating point rounding issues, but > > logically those integers are still real (or at least rational) numbers, > > and so we can speak of base, mantissa and exponent. The precision > > required is pretty large, much more than two digits. > > Integers in all languages I'm aware of are not stored as > mantissa/exponent, they're stored as bits with complete precision.
That's why I wrote "logically". Clearly, very, very clearly, int64_t is not a float, has no mantissa, no exponent. But you can use it as though an int64_t were a real (well, rational) number. > You can say you need a particular number of bits, but you'll never > lose the last bit (the 1s) just because your numbers have got too big. > You'll get an overflow error instead. Yes. > By 'two digits of precision' I was referring to cents for US dollars, > pence for pounds sterling, etc.. Some currencies have no fractional > part (e.g. Yen). And I was sure there were ... ah, here we are: Tenths of pennies are also used though. See just about any gas station in the U.S. Oh, I forgot, with 64-bit _signed_ ints you get one fewer digit of precision than I wrote earlier. Nico -- _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
