Unexpected result in round

[HPW]

Hello,



I get this unexpected result in round:

Code Select Expand


> (round 8.3 -1)
8.300000000000001
> (round 8.30 -1)
8.300000000000001
> (round 8.430 -1)
8.4
> (round 8.4 -1)
8.4
> (round 8.2 -1)
8.199999999999999
>


The doc contains not this behaviour.



Regards

Hans-Peter

[rrq]

If you don't mind, I would point you at this fairly in-depth discussion about "representable numbers"

https://en.wikipedia.org/wiki/Floating-point_arithmetic#Representable_numbers,_conversion_and_rounding">//https://en.wikipedia.org/wiki/Floating-point_arithmetic#Representable_numbers,_conversion_and_rounding

which I think is the issue at hand here.



In short, the numbers you see printed are the nearest representable numbers to the numbers you asked for, given that the rounding is done wrt a decimal base whilst the actual values are held in binary.

[Lutz]

If you are concerned about the visual representation use format:

Code Select Expand

> > (round 8.300 -1)
8.300000000000001

> (format "%2.1f" 8.300)
"8.3"
>


[HPW]

Hello,



Thanks for the advices.

I am generating nc-code for a nc-drilling mashine.

Format will do the Job.



Regards

Hans-Peter