Most efficient way to "clip" a value to repeat through a range?

Question

Given a value n, what would be the most efficient way of putting it in the range of [min, max] such that it will repeat through the range if it goes beyond it?

I don't know the term for this, so it's difficult to phrase the question, but maybe a truth table might help:

Where min = -2 and max = 3

 input  --> output
    -6      0
    -5      1
    -4      2
    -3      3
    -2     -2
    -1     -1
     0      0
     1      1
     2      2
     3     -2
     4     -1
     5      0
     6      1

What I have so far is this:

(value - min) % (max - min) + min;

Which works, but my worry is the modulus operator % is unreliable for negative inputs, from what I've read (output becomes implementation defined, rendering it useless, or at least unportable)

Is this the equation you're looking for ? `x % (max - min) + min` — Zohar81, Jun 14 '16 at 06:59
@MichaelWalz - I added it, and also fixed the truth table (the last three entries were incorrect) — Anne Quinn, Jun 14 '16 at 07:03
@2rd_7 - the modulus operator turns `3%3` to 0, so I just based the range around it (sorry, I initially messed that part up in the question) — Anne Quinn, Jun 14 '16 at 07:06
I suggest for clarity, the post should be retitled into something like: _Most efficient way of “clipping” values to **wrap inside** a range?_ — user3078414, Jun 14 '16 at 10:49

ammcom · Accepted Answer · 2016-06-14T07:20:04.980

1

it is like this:

min = VALUE;
max = VALUE;
x = (((x - min) + 1) % (max - min)) + min

here x will be inside min and max - 1 when you repeat the last line of code

EDIT:

and to match your exact table:

output = (input - min) % (max - min) + min;

EDIT 2:

if modulus is not defined for negative numbers:

if (input >= min)
    output = (input - min) % (max - min) + min;
else
    output = max - ((max - input) % (max - min));

edited Jun 14 '16 at 07:20

answered Jun 14 '16 at 06:54

ammcom

992
1
7
24

Will this work if `(input - min)` results in a negative number? I've read in C/C++, modulus on negative numbers isn't defined by the language (the sign of the result might be negative) – Anne Quinn Jun 14 '16 at 07:08

score 0 · Answer 2 · edited May 23 '17 at 12:24

0

If I understood your request correctly, here's the simplest equation i could think of : x % (max - min) + min

And here you can find some ways to optimize the modulo operator.

edited May 23 '17 at 12:24

Community

1
1

answered Jun 14 '16 at 07:06

Zohar81

4,554
5
29
82

Most efficient way to "clip" a value to repeat through a range?

2 Answers2