diff --git a/libraries/AP_Common/Bitmask.h b/libraries/AP_Common/Bitmask.h
new file mode 100644
index 0000000000..61b1d0df34
--- /dev/null
+++ b/libraries/AP_Common/Bitmask.h
@@ -0,0 +1,70 @@
+/*
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+/*
+  simple bitmask class
+ */
+
+class Bitmask {
+public:
+    Bitmask(uint16_t numbits) :
+        numwords((numbits+31)/32) {
+        bits = new uint32_t[numwords];
+    }
+    ~Bitmask(void) {
+        delete[] bits;
+    }
+
+    // set given bitnumber
+    void set(uint16_t bit) {
+        uint16_t word = bit/32;
+        uint8_t ofs = bit & 0x1f;
+        bits[word] |= (1U << ofs);
+    }
+
+    // clear given bitnumber
+    void clear(uint16_t bit) {
+        uint16_t word = bit/32;
+        uint8_t ofs = bit & 0x1f;
+        bits[word] &= ~(1U << ofs);
+    }
+
+    // clear all bits
+    void clearall(void) {
+        for (uint16_t i=0; i<numwords; i++) {
+            bits[i] = 0;
+        }
+    }
+    
+    // return true if given bitnumber is set
+    bool get(uint16_t bit) {
+        uint16_t word = bit/32;
+        uint8_t ofs = bit & 0x1f;
+        return (bits[word] & (1U << ofs)) != 0;
+    }
+
+    // return true if all bits are clear
+    bool empty(void) {
+        for (uint16_t i=0; i<numwords; i++) {
+            if (bits[i] != 0) {
+                return false;
+            }
+        }
+        return true;
+    }
+    
+private:
+    uint16_t numwords;
+    uint32_t *bits;
+};