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--- functions:mod [2017/03/15 14:52] – created korshun
+++ functions:mod [2017/07/15 12:13] (current) – korshun
@@ Line 1: / Line 1: @@
-{{tag>todo}}
+====== mod ======
+{{tag>math}}
+''num mod(num a, num b)''
+[[:types|num - any numeric type (int or fixed)]]
+===== Description =====
+This function implements modulo division ''a % b'', but, unlike the ACS operator, it handles negative values of ''a'' like mathematical modulo, making ''a'' cycle around on the range ''[0, b)''.
+This makes its result safe to use an array index, as the result is not negative for negative values of ''a''.
+Only positive values of ''b'' are supported.
+===== Examples =====
+<code>
+mod(-5, 3) -> 1
+mod(-4, 3) -> 2
+mod(-3, 3) -> 0
+mod(-2, 3) -> 1
+mod(-1, 3) -> 2
+mod(0, 3) -> 0
+mod(1, 3) -> 1
+mod(2, 3) -> 2
+mod(3, 3) -> 0
+mod(4, 3) -> 1
+mod(5, 3) -> 2
+</code>
+Using mod to implement menu cycling easily:
+<code>
+if (KeyPressed(BT_DOWN))
+    menuindex++;
+if (KeyPressed(BT_UP))
+    menuindex--;
+menuindex = mod(menuindex, NUM_MENU_ITEMS);
+</code>

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