Implement AIS protocol decoder

1 files changed, 93 insertions, 0 deletions

diff --git a/src/org/traccar/helper/BitBuffer.java b/src/org/traccar/helper/BitBuffer.java
new file mode 100644
index 000000000..7626988cc
--- /dev/null
+++ b/src/org/traccar/helper/BitBuffer.java
@@ -0,0 +1,93 @@
+/*
+ * Copyright 2016 Anton Tananaev (anton@traccar.org)
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.traccar.helper;
+
+import org.jboss.netty.buffer.ChannelBuffer;
+import org.jboss.netty.buffer.ChannelBuffers;
+
+public class BitBuffer {
+
+    private ChannelBuffer buffer = ChannelBuffers.dynamicBuffer();
+
+    private int writeByte;
+    private int writeCount;
+
+    private int readByte;
+    private int readCount;
+
+    public void writeEncoded(byte[] bytes) {
+        for (byte b : bytes) {
+            b -= 48;
+            if (b > 40) {
+                b -= 8;
+            }
+            write(b);
+        }
+    }
+
+    public void write(int b) {
+        if (writeCount == 0) {
+            writeByte |= b;
+            writeCount = 6;
+        } else {
+            int remaining = 8 - writeCount;
+            writeByte <<= remaining;
+            writeByte |= b >> (6 - remaining);
+            buffer.writeByte(writeByte);
+            writeByte = b & ((1 << (6 - remaining)) - 1);
+            writeCount = 6 - remaining;
+        }
+    }
+
+    public int readUnsigned(int length) {
+        int result = 0;
+
+        while (length > 0) {
+            if (readCount == 0) {
+                readByte = buffer.readUnsignedByte();
+                readCount = 8;
+            }
+            if (readCount >= length) {
+                result <<= length;
+                result |= readByte >> (readCount - length);
+                readByte &= (1 << (readCount - length)) - 1;
+                readCount -= length;
+                length = 0;
+            } else {
+                result <<= readCount;
+                result |= readByte;
+                length -= readCount;
+                readByte = 0;
+                readCount = 0;
+            }
+        }
+
+        return result;
+    }
+
+    public int readSigned(int length) {
+        int result = readUnsigned(length);
+        int signBit = 1 << (length - 1);
+        if ((result & signBit) == 0) {
+            return result;
+        } else {
+            result &= signBit - 1;
+            result += ~(signBit - 1);
+            return result;
+        }
+    }
+
+}