#320 json plugin value anomaly

[Anonymous]

Originally created by: keszegh

using json.decode
many times if i have a value stored as -139.89
the value restored is -139.88999999999999
etc with most of the values i store like this (all have 2 precision digits like this one).

[Anonymous]

Originally posted by: ar2rsawseen

It is not a json problem per se, but rather floating point precision problem and how computer stored floating points. So it is mostly Lua or C specific and only thing is to round up the number to what you expect it to be, like 2 number precision
http://lua-users.org/wiki/SimpleRound

More info:
http://stackoverflow.com/questions/3580486/lua-subtracting-decimal-numbers-doesnt-return-correct-precision

[Anonymous]

Originally posted by: keszegh

perhaps it could be done on the c side to make it faster?
or if this adds a performance hit then it would be good to be able to add to json decode/encode the required precision as a parameter.

[Anonymous]

Originally posted by: ar2rsawseen

Can't really do that I think, there could be multiple floats in json which require different precision

[Anonymous]

Originally posted by: keszegh

thanks for the info.
and btw. at least if i store an integer, then they remain an integer, right?

[Anonymous]

Originally posted by: ar2rsawseen

actually I think in Lua all numbers are stored as double underneath, but for integer, without point, at least it can be determined that expected value is integer and is probably rounded internally.