multipleOf validation and decimals - the floating number problem ...

Hey Geraint,

you should not use the modulo operator for validating multipleOf if validating decimals.
See e.g.
http://stackoverflow.com/questions/16909104/how-to-check-whether-an-integer-is-divisible-by-a-decimal

The JSON Schema latest spec. says multipleOf is for integer and number and
"A numeric instance is valid against "multipleOf" if the result of the division of the instance by this keyword's value is an integer."

For now tv4 / multipleOf returned false for some decimal numbers which SHOULD be true
Consider 6.6 multipleOf 2.2 ----> is invalid for tv4
while 6.6666 multipleOf 2.2222 -> is valid for tv4 !

I think this is not very straightforward.

I made a fiddle to experiment with it
http://jsfiddle.net/we1nt9ye/1/
What do you think of "Alternative 2" ?

btw:
There might be better things for bigger decimals like
https://github.com/dtrebbien/BigDecimal.js
or
https://github.com/MikeMcl/big.js/
or
https://github.com/MikeMcl/decimal.js/

[geraintluff]

So the main issue here is that 2.2*3 !== 6.6, yes?

So whatever form it takes, I guess what you're proposing is that we add a bit of wiggle-room to the comparison, to allow for floating-point nonsense? In that case, why not something like:

var CLOSE_ENOUGH = Math.pow(2, -51);
var remainder = (num/factor)%1;
return (remainder <= CLOSE_ENOUGH || remainder >= 1- CLOSE_ENOUGH);

👍 Yep, exactly - that is totally fine for validation.
Could you implement it and then close this isssue ?

You may ask why I came up with the stringish solution (which is basically bad).
I am the one writing the graph API maker (from the google group, coding 'live' again).
I implemented tv4. It is totally fine.
My schemer (AMD) should be as modular as possible, e.g. I have a default dojo/dijit widget for each type.
I was trying to handle the exception where a user may use modules of the code to 'bind' a (sub)schema to native input elements only having a string value. But I think I'll skip that.
Think of a visual calculator. A bad example - if a user wants to calculate 6.6 / 2.2 here: http://thecodeplayer.com/walkthrough/javascript-css3-calculator it would not output 3 ;)

an additional idea for readme.md last lines
Something like "Do you speak another language? This project needs internationalization. See https://github.com/geraintluff/tv4/tree/master/lang"

[geraintluff]

Sure - I'll give it some time this evening.

Pull Requests are always appreciated, btw, including things like README changes. :)

I made a pull request from that here: #168