Quick Question about "Mod" operator

I've been searching through the forums and the help file that came with MMF2, but none can tell what the "Mod" operator does in the expression editor to different numbers, they only point out that it is there. I've never used it but can someone tell what it does to numbers and why it is included?

Thanks, Hughster

http://en.wikipedia.org/wiki/Modulo_operation

It basically divides two numbers and returns the remainder.

Its especially useful when dealing with 2 or more dimensions.

For example (1D-2D)

let V='1D and W='x width' position' then in 2d

x=V MOD W

y=(v-(V MOD W))/w

As a more practical whatever example:

1 mod 3 = 1
2 mod 3 = 2
3 mod 3 = 0
5 mod 3 = 2
8 mod 3 = 2
8 mod 3 = 0

By practical you mean incorrect?
8 mod 3 = 2

I think of mod as a circle. Once you've reached the desired end you go back to the start.

It's just a shame most mod implementations don't handle negative numbers.. that'd be so much more useful (although I saw some that did before.. not sure in which language though) - especially with rotations.

And an even more practical example:

128 seconds:
128 / 60 = 2
128 mod 60 = 8

128 seconds = 2 minutes and 8 seconds

Quote:

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Originally Posted by Random

It's just a shame most mod implementations don't handle negative numbers.. that'd be so much more useful (although I saw some that did before.. not sure in which language though) - especially with rotations.

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I think it does, but like this:
-128 / 60 = -2
-128 mod 60 = -8

To wrap it positive IIRC you do this:
((number mod limit) + limit) mod limit)

Try abs(negative number)

Quote:

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Try abs(negative number)

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What?

Thats how to get it to work with negative numbers.

Thanks, although I'll still probably never use it since I have no programming skills, it's useful to know what it is just in case. And thanks for the examples.

Quote:

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Originally Posted by dragonguy

Try abs(negative number)
Thats how to get it to work with negative numbers.

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Actually no. abs(-2) is 2, when you'd expect it to be 30 using mod. Think directions: 0 = 32, -1 = 31, -2 = 30...

Quote:

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Try abs(negative number)

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*ignore*

Quote:

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I think it does, but like this:
-128 / 60 = -2
-128 mod 60 = -8

To wrap it positive IIRC you do this:
((number mod limit) + limit) mod limit)

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Indeed. I don't find it very practical though. I've seen implementations where -128 mod 60 is 52. I find it rather annoying to have to write it the complicated way all the time, but then I guess I'm just lazy.

According to wikipedia there are three common ways to implement modulo. I suppose then it's down to luck which one you get with your development environment..

Euclidean definition ftw! I wish MMF2 used this.

The mod function has heaps of uses - here's a couple more...

To determine if a number is odd or even:
if "Number" mod 2 = 0, then "Number" is even
if "Number" mod 2 = 1, then "Number" is odd


To find the difference between two angles:
((Angle1 - Angle2 + 540) mod 360) - 180

It essentially tells you whether to rotate clockwise or counter-clockwise, depending on whether the result is positive or negative.


To load a tile-based map from an array, using a fast loop:
XPosition = LoopIndex(">Fastloop<") mod DimX( ">Array<" )
YPosition = LoopIndex(">Fastloop<") / DimX( ">Array<" )