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rounding cycle interrogation ?..

DSP related issues, mathematics, processing and techniques

rounding cycle interrogation ?..

Postby Tepeix » Mon Mar 21, 2022 5:16 pm

Just a simple float counters.

Every time it go > 4096 it's get - 4096.

(seams to works well but not if the input value is > 4096... I need to test it more..)

What seams strange is the first cycle with an 0.1 input value will make 0.1 when -4096 occurs.
Then next cycle it become 0.449. then 0.0347. then 0.0244, 0.0142, 0.0039, ... ...

Did you know what cause this strange rounding behavior ?
Is there any use to try to fix this ?

Thanks for any response ;)
Attachments
Float count.fsm
(62.74 KiB) Downloaded 444 times
Tepeix
 
Posts: 350
Joined: Sat Oct 16, 2021 3:11 pm

Re: rounding cycle interrogation ?..

Postby Tepeix » Mon Mar 21, 2022 7:25 pm

I try a different approach with this code :
Code: Select all
streamin in;
streamout out;
float index=0;
float max=4096;
movaps xmm0,in;
addps xmm0,index;
movaps xmm1,xmm0;
cmpps xmm1,max,5;
andps xmm1,max;
subps xmm0,xmm1;
movaps index,xmm0;
movaps out,xmm0;

But i get exatly the same result ... ..
Tepeix
 
Posts: 350
Joined: Sat Oct 16, 2021 3:11 pm

Re: rounding cycle interrogation ?..

Postby Tepeix » Mon Mar 21, 2022 9:31 pm

Another approach...

This time a float ramp from 0 to 1. That feed a int counter from 0 to 4095..
And finally the added result.
That's a little more stable. But it never go to 0.. Or maybe after a long time ?
The max value change a little. A 0.0005 imprecision for both..

Also if i check the counter.. There's a lot of variation after 0.1. Like it always add something like 0.10001 ?
Attachments
floatcount other way2.fsm
(added comment about the int output)
(98.06 KiB) Downloaded 414 times
Last edited by Tepeix on Mon Mar 21, 2022 10:18 pm, edited 2 times in total.
Tepeix
 
Posts: 350
Joined: Sat Oct 16, 2021 3:11 pm

Re: rounding cycle interrogation ?..

Postby Tepeix » Mon Mar 21, 2022 10:11 pm

Finally, this one seams to works with no rounding problems. (at least for 0.1 input !)

The float ramp go from -0.5 to 0.5. > feed the int counter.
Then adding 0.5 to the float. Adding the int. It seams ok for now ;)

(Note that this code and the last one have a blue int output.
If you connect it to a code that treat it as a float it will take cpu and give bad result..)
Attachments
floatcount other way3.fsm
edit (little stage0; forgotten instructions erased)
(98.11 KiB) Downloaded 420 times
Tepeix
 
Posts: 350
Joined: Sat Oct 16, 2021 3:11 pm

Re: rounding cycle interrogation ?..

Postby tulamide » Wed Mar 23, 2022 12:59 am

I'm not sure, what goal you try to reach?
float values are imprecise by nature, you can't rely on them. If you want to make sure to get a stable start and end point, you have to use linear interpolation. If you try to get exact steps per sample, you need to use integer numbers (note, integer numbers, not the integer format). In other words steps like +1 or +13, instead of 0.1 or 1.3.
"There lies the dog buried" (German saying translated literally)
tulamide
 
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Location: Germany

Re: rounding cycle interrogation ?..

Postby Tepeix » Wed Mar 23, 2022 1:11 pm

Thanks !

I was thinking that float would be imprecise when using very small number but not specially with 0.1.

Not really sure what i try to do.. But the main purpose is an lfo reading mem.
Maybe an osc, but i think it would be impossible to bandlimit it..

Maybe for an lfo i don't need so much precision...
The 4096 choice also could be to much..

But the int think attract me ;) I first try with true int then i read again your message ;)
Tepeix
 
Posts: 350
Joined: Sat Oct 16, 2021 3:11 pm

Re: rounding cycle interrogation ?..

Postby Tepeix » Wed Mar 23, 2022 6:33 pm

Héhé, the guy that try to utilize green ticker to blue, then complain about blue float precision ;) :oops:
Tepeix
 
Posts: 350
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