Timeline for Addition modulo 26 in Digital Logic
Current License: CC BY-SA 3.0
12 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Apr 12, 2013 at 22:58 | vote | accept | captncraig | ||
| Apr 11, 2013 at 21:51 | comment | added | supercat | @Andyaka: The question is how to reduce a 6-bit number which is known to be in the range 0-50 modulo 26. It's worthwhile to note that what is required here is much like BCD arithmetic (except modulo 26 rather than modulo 10), and processors with BCD support generally behave oddly when adding two digits whose sum (including carry in) is greater than 19. | |
| Apr 11, 2013 at 21:45 | answer | added | fgrieu | timeline score: 1 | |
| Apr 11, 2013 at 21:26 | answer | added | Dave Tweed | timeline score: 6 | |
| Apr 11, 2013 at 21:18 | comment | added | Andy aka | The S+(32-26)+32 is a cool idea @supercat. In above comment I meant test for =>26 | |
| Apr 11, 2013 at 21:15 | comment | added | Andy aka | Getting the remainder after subtracting 26 seems a good approach but... you need to test if the number is greater than 26 first. I believe this can be done with two ANDs and two ORs. Then you'll need to test the remainder in (in case it was 52 or greater originally) and possibly subtract 26 once more? OK just seen that the original numbers were<26 | |
| Apr 11, 2013 at 20:39 | comment | added | Tim | There's not many 'tricks' you can do for modulo in digital logic (assuming you're not doing mod power of two). It's essentially a messy division operation or looping and subtracting. I would expect any solution to this to feel a bit 'clunky'. | |
| Apr 11, 2013 at 20:36 | comment | added | captncraig | @Andy, yes. That is what I need. | |
| Apr 11, 2013 at 20:32 | comment | added | Andy aka | Is this your question in a nutshell... How do I convert a 6 bit number to mod 26? | |
| Apr 11, 2013 at 20:21 | comment | added | supercat | Could the result of computing S-26 be used somehow to determine whether S is greater than 25? Also, since S-26 is the same as S+(32-26)-32, might it be conceptually easier to think in terms of computing (S+6) and dropping the high bit? | |
| Apr 11, 2013 at 19:49 | comment | added | Brian Carlton | Why would you want to do this? Is this homework? | |
| Apr 11, 2013 at 19:45 | history | asked | captncraig | CC BY-SA 3.0 |