round vs pcRound (rounding floating numbers)

Hi Adrian,

Having looked at the description and the code for pcRound, I really cannot see the point of pcRound - it seems an unnecessarily complicated way of not quite rounding to the nearest integer. It was intended for use in PCells - I've never used it though. I can't actually see the benefit of the controls that you have for the additional arguments. I found the original CCR where it was enhanced to provide control, and another which was an attempt to explain what it did - it's as clear as mud though.

So I'd stick to using round - at least it's obvious what it is doing.

I would have thought that if rounding to the nearest integer, you wouldn't be that bothered whether the number is 3.499 or 3.49999 or 3.500001 or whatever - rounding errors occurring half way between the numbers would mean that you are close to either direction and it probably doesn't matter - it just depends on the application. If it depends on the application, you want to have precise control over how rounding works for your application rather than depending on some mysterious function.

Regards,

Andrew.

Hi Adrian,

Having looked at the description and the code for pcRound, I really cannot see the point of pcRound - it seems an unnecessarily complicated way of not quite rounding to the nearest integer. It was intended for use in PCells - I've never used it though. I can't actually see the benefit of the controls that you have for the additional arguments. I found the original CCR where it was enhanced to provide control, and another which was an attempt to explain what it did - it's as clear as mud though.

So I'd stick to using round - at least it's obvious what it is doing.

I would have thought that if rounding to the nearest integer, you wouldn't be that bothered whether the number is 3.499 or 3.49999 or 3.500001 or whatever - rounding errors occurring half way between the numbers would mean that you are close to either direction and it probably doesn't matter - it just depends on the application. If it depends on the application, you want to have precise control over how rounding works for your application rather than depending on some mysterious function.

Regards,

Andrew.

Hi Andrew, thanks for confirming my thoughts regarding pcRound   
I understand what you say regarding the rounding.
My problem is that, because of this, some PCells are not behaving in the same way for some of the parameters.

Trying to enlarge the first testcase to demonstrate my problem, I have the following situations:

procedure( myCalc(x)
     let( (a)
         a = ( 26.40 - x ) / 2.0
         round(a/0.01) * 0.01 ;;return
     )
)  
for(i 1481 1490 printf("%f\n" myCalc(i/100.0)) )

5.790000
5.790000
5.780000
5.780000
5.770000
5.770000
5.770000
5.760000
5.750000
5.750000

Because of the rounding issue, I get some unexpected & repeated numbers in my sequence .... e.g.: I was expecting a 5.76. not 5.77 on the 7th position in my list.

Unfortunately ("unfortunately" because "pcRound" looks so strange) pcRound doesn't give me these kind of issues...

Another solution for me is to round 2 times, to get rid of the additional digits of the floting number ....  but this is ugly:
a=  round( a/0.001) * 0.001
round(a/0.01) * 0.01

If you have in mind any other more reliable solution, please let me know.
Thanks,
BR,
Adrian

Hi Adrian,

Here's what I'd do:

The small offset moves you above the rounding error which ends you at n.49999999999

procedure( myCalc(x)
     let( (a)
         a = ( 26.40 - x ) / 2.0
	 ;printf("debug: %.16g\n" a/0.01)
	 ;printf("pc: %g\n" pcRound(a/0.01)*0.01)
	 ; add a small offset to account for rounding errors
         round(a/0.01+0.001) * 0.01 ;;return
     )
)  
for(i 1481 1490 printf("%f\n" myCalc(i/100.0)) )

Regards,

Andrew