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authorAnton Tananaev <anton.tananaev@gmail.com>2016-12-18 23:33:42 +1300
committerAnton Tananaev <anton.tananaev@gmail.com>2016-12-18 23:33:42 +1300
commit99f09134fb9c710114296d603c97a76f5cfb0d2a (patch)
tree6484204ead4eb8a5636bbcc234534545a18fbeac /src/org/traccar/helper/BitBuffer.java
parent9d548e3aab48e9f13c51c5f974b06e29db8d1d0c (diff)
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Implement AIS protocol decoder
Diffstat (limited to 'src/org/traccar/helper/BitBuffer.java')
-rw-r--r--src/org/traccar/helper/BitBuffer.java93
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
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+++ 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;
+ }
+ }
+
+}