On Wednesday, 20 April 2016 15:18:06 UTC+1, Stefan Karpinski wrote: > > IEEE has not made the programming language designer's life easy here. >
Perhaps it's a subtle attempt to incentivise more designers of mathematical programming languages into IEEE standards committees?! > > On Wed, Apr 20, 2016 at 5:51 AM, Milan Bouchet-Valat <nali...@club.fr > <javascript:>> wrote: > >> Le mardi 19 avril 2016 à 22:10 -0700, Jeffrey Sarnoff a écrit : >> > Hi, >> > >> > You have discovered that IEEE standard floating point numbers have >> > two distinct zeros: 0.0 and -0.0. They compare `==` even though they >> > are not `===`. If you want to consider +0.0 and -0.0 to be the same, >> > use `==` or `!=` not `===` or `!==` when testing floating point >> > values (the other comparisons <=, <, >=, > treat the two zeros as a >> > single value). >> There's actually an open issue about what to do with -0.0 and NaN in >> Dicts: https://github.com/JuliaLang/julia/issues/9381 >> >> It turns out it's very hard to find a good solution. >> >> >> Regards >> >> > > Hello everyone! >> > > I was wondering if the following behavior of round() has an special >> > > purpouse: >> > > >> > > a = round(0.1) >> > > 0.0 >> > > >> > > b = round(-0.1) >> > > -0.0 >> > > >> > > a == b >> > > true >> > > >> > > a === b >> > > false >> > > >> > > bits(a) >> > > "0000000000000000000000000000000000000000000000000000000000000000" >> > > >> > > >> > > bits(b) >> > > "1000000000000000000000000000000000000000000000000000000000000000" >> > > >> > > So the sign stays around... >> > > >> > > I am using this rounded numbers as keys in a dictionary and julia >> > > can tell the difference. >> > > >> > > For example, I expected something like this: >> > > dict = [i => exp(i) for i in [a,b]] >> > > Dict{Any,Any} with 1 entry: >> > > 0.0 => 1.0 >> > > >> > > but got this: >> > > dict = [i => exp(i) for i in [a,b]] >> > > Dict{Any,Any} with 2 entries: >> > > 0.0 => 1.0 >> > > -0.0 => 1.0 >> > > >> > > It is not a big problem really but I would like to know where can >> > > this behaviour come handy. >> > > >> > > Cheers! >> > > >> > >
