# HG changeset patch
# User Eugen Sawin <sawine@me73.com>
# Date 1308082339 -7200
# Node ID b3a61fa4c8d768784b2ff4d4b202135a60e4c0ac
# Parent  aa4e1ccda9ab0e9ae7c93388d74537c059c4365d
Added double hash.

diff -r aa4e1ccda9ab -r b3a61fa4c8d7 src/double_hash.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/double_hash.py	Tue Jun 14 22:12:19 2011 +0200
@@ -0,0 +1,39 @@
+"""
+Name: string_hash -  a string hashing program
+Description: Basic string hashing program according to Theory I lecture.
+Author: Eugen Sawin <sawine@informatik.uni-freiburg.de>
+"""
+
+def main():    
+    args = parse_arguments()
+    used = set()
+    for key in args.values.split():
+        print "%s: %i" % (key, double_hash(int(key), used))
+
+def double_hash(k, used):
+    j = 0
+    code = (h(k) - s(j, k)) % 15
+    while code in used:
+        j += 1
+        code = (h(k) - s(j, k)) % 15
+    used.add(code)
+    return code
+
+def s(j, k):
+    return j * h2(k)
+
+def h(k):
+    return k % 15
+
+def h2(k):
+    return 1 + (k % 13) 
+
+from argparse import ArgumentParser
+
+def parse_arguments():
+    parser = ArgumentParser(description="Returns the hash for given string using the double-hash technique.")
+    parser.add_argument("values", help="values")    
+    return parser.parse_args()
+
+if __name__ == "__main__":
+    main()