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Test_Cases/IP_Checksum_Calculator.py

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+# Code has been taken from https://www.codeproject.com/Tips/460867/Python-Implementation-of-IP-Checksum
+# Example is provided at https://www.thegeekstuff.com/2012/05/ip-header-checksum/
+
+def ip_checksum(ip_header, size):
+    
+    cksum = 0
+    pointer = 0
+    
+    #The main loop adds up each set of 2 bytes. They are first converted to strings and then concatenated
+    #together, converted to integers, and then added to the sum.
+    while size > 1:
+        cksum += int((str("%02x" % (ip_header[pointer],)) + 
+                      str("%02x" % (ip_header[pointer+1],))), 16)
+        size -= 2
+        pointer += 2
+    if size: #This accounts for a situation where the header is odd
+        cksum += ip_header[pointer]
+        
+    cksum = (cksum >> 16) + (cksum & 0xffff)
+    cksum += (cksum >>16)
+    
+    return (~cksum) & 0xFFFF
+
+
+if __name__=="__main__":
+    
+    header = {}
+
+    header[0] = 0x45
+    header[1] = 0x00
+    header[2] = 0x00
+    header[3] = 0x28
+    header[4] = 0x00
+    header[5] = 0x02
+    header[6] = 0x00
+    header[7] = 0x00
+    header[8] = 0x28
+    header[9] = 0x06
+    header[10] = 0xfd    
+    header[11] = 0x5f
+    header[12] = 0xc0
+    header[13] = 0xa8
+    header[14] = 0x0a
+    header[15] = 0x14
+    header[16] = 0xc0
+    header[17] = 0xa8
+    header[18] = 0x0a
+    header[19] = 0x0a
+   
+    print("Checksum is: %x" % (ip_checksum(header, len(header)),))