Question

In brief – I am having a hard time with the float left overs
(i.e. 10.00000123 instead of 10)

Here I go :

I need to generate list of floats with constant gap as follows
(actually its a map , I need to retreive the object nut nevermind that)

List A: 0.25, 0.5, 0.75, 1, …
or
List B: 0.01, 0.02, 0.03, 0.04, …

every time I get a number and I round it to the neerest cell in the list.
lets say I get 0.051 to retreive a cell in list A – I return 0.05.
lets say I get 0.21 to retreive a cell in list B – I return 0.25.

So I started be doing this

float a = Math.round(Value / step) * step;

but than I get a lot of time 0.2500001 (float leftovers )
I need a smart way to round it .

Maybe by taking the number of digits after the dot and doing again

Math.round(Value / 100) * 100;?

Is there a smarter way?
I tried doig this

        final float factor = Math.round(1 / step);
        final float value = (float) Math.round(value * factor) / factor;

but I sometimes have a list like this

List A: 10, 15 , 20, 25, 30, …

and when I get 22 I retreive the cell of 20.
the problem is that When I get a gap of 10

Math.round(1 / baseAssetStep) 

returns 0 – and I get NaN

Answer 1

In short, “these are not the numbers you’re looking for.”

Floating points are represented as binary fractional numbers, and some numbers that can be easily represented in base-10 (0.01, for instance) can’t be represented with a finite number of binary digits. This is similar to how 1/3 is easy in base 3 (it’s just 0.1), but requires an infinite number of digits in base 10 (0.333…).

If you tried to represent 1/3 with a finite number of digits in base 10, you’d get an approximation. Similarly, if you try to represent 1/10 with a finite number of digits in base 2 (which is what float and double do), you’ll get an approximation, and similarly with 1/100. What you think is 0.01 in the code is actually a number that’s very close, but not exactly equal to, 1/100.

There are many resources out there concerning floating points and the difficulty in working with them. http://floating-point-gui.de/ is a good place to start.