I'm writing a finance app and was looking for solutions to the precision problem. I found some stuff. I have not tested any of it as at first glance this all thing feels overkill. There may be a more elegant solution. bigdecimal.js part of gwt-math http://code.google.com/p/gwt-math/source/browse/trunk/gwt-math/js_originals/bigdecimal.js BigDecimal support for JavaScript http://stz-ida.de/html/oss/js_bigdecimal.html.en Big Number http://jsfromhell.com/classes/bignumber On Sat, Dec 12, 2009 at 1:18 PM, Leo Simons wrote: > On 12/12/09 12:33 PM, Michael Franzkowiak wrote: >> >> CouchDB seems to think that 0.79 + 5.99 + 1.59 = 8.370000000000001 > > So does most other software when using floating point arithmetic: > > \$ python -c 'print "%.15f" % (0.79 + 5.99 + 1.59)' > 8.370000000000001 > \$ perl -e 'print sprintf("%.15f\n", 0.79 + 5.99 + 1.59);' > 8.370000000000001 > \$ python -c 'print "%.20f" % (0.79 + 5.99 + 1.59)' > 8.37000000000000099476 > \$ perl -e 'print sprintf("%.20f\n", 0.79 + 5.99 + 1.59);' > 8.37000000000000099476 > > This is standard stuff ( > http://docs.sun.com/source/806-3568/ncg_goldberg.html ). > >> I could always just multiply my numbers with the precision I need > >> and work with ints but I'm still curious to see this explained. > > What you really really want is a decimal type: > > \$ python -c 'from decimal import Decimal; print Decimal("0.79") + > Decimal("5.99") + Decimal("1.59")' > 8.37 > > ...but there is no decimal type in javascript or json so also does not exist > in CouchDB. > > Looks like you're representing money; just work with cents (stored as ints) > and you will *probably* be fine, especially if you stay clear of divisions. > I wouldn't try and implement my own finance package that way, though :) > > Alternatively, implement your own decimal type in javascript, or use a > relational database :) > > ciao, > > Leo > -- :Matteo Caprari matteo.caprari@gmail.com