divmod10() : a fast replacement for /10 and %10 (unsigned)

[robtillaart]

Thanks Paul,

We can propose on the developers list that the divmod10 code (including #ifdef  to select asm or C version) becomes a separate .h file within the core.  I've seen " x/10 x%10" code constructs in several libs
(recently - http://forum.arduino.cc//index.php?topic=190472.0 - )

what do you think?

update: the divmod.h (?) could include work discussed here - http://forum.arduino.cc//index.php?topic=172635.0 -

[pjrc]

I think it's a good idea.

But I also find proposing stuff on the developer mail list to be exhausting.  I'm not personally planning to propose it and respond to the many "bike shedding" replies that are likely to result.

If you propose it, I'll chime in with a "+1".  When/if Arduino publishes it, I'll adopt whatever naming and header file convention they use.

[pjrc]

If you do write up a good proposal on the developer mail list and Cristian replies favorably (really, anything other than saying no or probably not), perhaps I'll adopt it for Teensyduino 1.17 or 1.18?  I just posted the first release candidate today.  I don't have a deadline for 1.17, but unless there's any problems or other urgent stuff to add, I'll probably release sometime next week.

I can't see the harm in placing this into a header where it can be used by libraries.  There just needs to be some consensus from Arduino (where really, Cristian's voice is the only one that matters) so I don't end up publishing this in a way that will later break when/if they do it.

[odometer]

Personally, I would love to see it wrapped in a function which, for purposes of this post, I shall call digit().

Code: [Select]


Example use of digit():
long n = 4216738;
byte ones = digit(n, 0);  // now, ones == 8
byte tens = digit(n, 1);  // now, tens == 3
byte hund = digit(n, 2);  // now, hund == 7
byte thou = digit(n, 3);  // now, thou == 6
byte myri = digit(n, 4);  // now, myri == 1
byte lakh = digit(n, 5);  // now, lakh == 2
byte mill = digit(n, 6);  // now, mill == 4
byte cror = digit(n, 7);  // now, cror == 0

This would be extremely useful for displays.

I'm not sure how it should behave for negative numbers, though.

[Tom Carpenter]

for negatives you would have to first negate to make them positive, then use divmod10 then negate the resulting division value (the mod value I believe would stay positive). If you are doing it multiple times in a row then you would leave the results all positive and then at the very end negate the remaining division part.

[robtillaart]

Personally, I would love to see it wrapped in a function which, for purposes of this post, I shall call digit().

Code: [Select]


Example use of digit():
long n = 4216738;
byte ones = digit(n, 0);  // now, ones == 8
byte tens = digit(n, 1);  // now, tens == 3
byte hund = digit(n, 2);  // now, hund == 7
byte thou = digit(n, 3);  // now, thou == 6
byte myri = digit(n, 4);  // now, myri == 1
byte lakh = digit(n, 5);  // now, lakh == 2
byte mill = digit(n, 6);  // now, mill == 4
byte cror = digit(n, 7);  // now, cror == 0

This would be extremely useful for displays.

I'm not sure how it should behave for negative numbers, though.

@odometer
Have you seen this thread, - http://forum.arduino.cc/index.php?topic=179111.0 -
it uses divmod10 to increase the speed of the print class from which display classes are derived. But also the Serial class is derived from Print.

[samepaul]

hi Rob

I know that Arduino code mainly uses LGPL license, but since this topic is not source code it can have less restrictive licensing.
Unfortunately for my project (not related to Arduino) I cannot use any license requiring exposure of proprietary sources.
Could you please license your algorithm on same terms as the Hacker Delight's book?

Thanks in advance

[odometer]

Could you please license your algorithm on same terms as the Hacker Delight's book?

What a strange world we live in, in which dividing two numbers requires a license!

[westfw]

Copying someone's code requires a license, regardless of what it does.