From aff7e147de507f3026de8d703ac166cb6214e55f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Fernando=20Merc=C3=AAs?= <fernando@mentebinaria.com.br>
Date: Fri, 12 Dec 2014 11:31:06 -0200
Subject: first commit

---
 unpacker.c | 86 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 86 insertions(+)
 create mode 100644 unpacker.c

(limited to 'unpacker.c')

diff --git a/unpacker.c b/unpacker.c
new file mode 100644
index 0000000..9d0e14b
--- /dev/null
+++ b/unpacker.c
@@ -0,0 +1,86 @@
+/*
+
+This source code is part of the AIS BlackToolkit.
+Unpacker.c allows you to build a NMEA sentece out of its payload. Normally used in combination with AIVDM_Encoder.
+ 
+Copyright 2013-2014 -- Embyte & Pastus
+
+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 2
+of the License, or (at your option) any later version.
+
+Usage example: 
+$ ./AIVDM_Encoder.py --type=1 --vsize=30x10 | xargs -IA ./unpacker A 1 A
+
+*/
+
+
+#include <sstream>
+#include <ctype.h>
+#include <stdio.h>
+#include <iostream>
+#include <iomanip>
+#include <string.h>
+
+unsigned long unpack(char *buffer, int start, int length)
+{
+    unsigned long ret = 0;
+    for(int i = start; i < (start+length); i++) {
+	ret <<= 1;
+	ret |= (buffer[i] & 0x01);
+    }
+    return ret;
+}
+
+char nmea_checksum(std::string buffer)
+{
+    unsigned int i = 0;
+    char sum = 0x00;
+    if(buffer[0] == '!') i++;
+    for(; i < buffer.length(); i++) sum ^= buffer[i];
+    return sum;
+}
+
+
+int main(int argc, char *argv[]) {
+
+
+	if (argc<4) {
+		std::cout << "\nUsage: ./unpacker binary_string enable_nmea channel\n";
+		std::cout << "\nenable_nmea = 1 for full NMEA sentence, otherwise only payload is printed\n";
+		std::cout << "channel = A/B\n\n";
+		return 0; 
+	}
+
+	int i;
+	char asciidata[255];
+
+	int len = strlen(argv[1]);
+	
+	int enable_nmea = (int) *argv[2] - 48;
+	char channel = *argv[3];
+	std::ostringstream d_payload;
+	d_payload.str("");
+	
+	for(i = 0; i < len/6; i++) {
+		asciidata[i] = unpack(argv[1], i*6, 6);
+		if(asciidata[i] > 39) asciidata[i] += 8;
+			asciidata[i] += 48;
+	}
+
+	if (enable_nmea)
+	    d_payload << "!AIVDM,1,1,," << channel << ",";
+
+    for(int i = 0; i < len/6; i++) 
+    	d_payload << asciidata[i];
+    
+    if (enable_nmea) {
+		d_payload << ",0"; //number of bits to fill out 6-bit boundary
+		char checksum = nmea_checksum(std::string(d_payload.str()));
+		d_payload << "*" << std::setw(2) << std::setfill('0') << std::hex << std::uppercase << int(checksum);
+    }
+
+	std::cout << std::string(d_payload.str()) << std::endl;	
+	return 1;
+}
-- 
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