add doc/mod/ipcalc

(cherry picked from commit e9953c361267f10fd15d3280ccd985062c1dde28)

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diff --git a/README.md b/README.md
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--- a/README.md
+++ b/README.md
@@ -240,6 +240,7 @@ Available modules
 * [Manage ports in bridge](doc/mod/bridge-port-to.md)
 * [Manage VLANs on bridge ports](doc/mod/bridge-port-vlan.md)
 * [Inspect variables](doc/mod/inspectvar.md)
+* [IP address calculation](doc/mod/ipcalc.md)
 * [Send notifications via Matrix](doc/mod/notification-matrix.md)
 * [Send notifications via Telegram](doc/mod/notification-telegram.md)
 
diff --git a/doc/mod/ipcalc.d/ipcalc.avif b/doc/mod/ipcalc.d/ipcalc.avif
new file mode 100644
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+++ b/doc/mod/ipcalc.d/ipcalc.avif
diff --git a/doc/mod/ipcalc.d/ipcalcreturn.avif b/doc/mod/ipcalc.d/ipcalcreturn.avif
new file mode 100644
index 0000000..d858bb1
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diff --git a/doc/mod/ipcalc.md b/doc/mod/ipcalc.md
new file mode 100644
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@@ -0,0 +1,53 @@
+IP address calculation
+======================
+
+[◀ Go back to main README](../../README.md)
+
+> ℹ️️ **Info**: This module can not be used on its own but requires the base
+> installation. See [main README](../../README.md) for details.
+
+Description
+-----------
+
+This module adds functions for IP address calculation.
+
+Requirements and installation
+-----------------------------
+
+Just install the module:
+
+    $ScriptInstallUpdate mod/ipcalc;
+
+Usage and invocation
+--------------------
+
+### IPCalc
+
+The function `$IPCalc` prints information to terminal, including:
+
+* address
+* netmask
+* network in CIDR notation
+* minimum host address
+* maximum host address
+* broadcast address
+
+It expects an IP address in CIDR notation as argument.
+
+    $IPCalc 192.168.88.1/24;
+
+![IPCalc](ipcalc.d/ipcalc.avif)
+
+### IPCalcReturn
+
+The function `$IPCalcReturn` expects an IP address in CIDR notation as
+argument as well. But it does not print to terminal, instead it returns
+the information in a named array.
+
+    :put ([ $IPCalcReturn  192.168.88.1/24 ]->"broadcast");
+
+![IPCalcReturn](ipcalc.d/ipcalcreturn.avif)
+
+---
+[◀ Go back to main README](../../README.md)  
+[▲ Go back to top](#top)