donarb · February 16, 2016 05:29 · Feb 16, 2016 · May 8, 2015
diff --git a/verhoeff_alpha.py b/verhoeff_alpha.py
@@ -1,7 +1,7 @@
 #!/usr/bin/env python
 
 """
-Python derivative of alphanumeric derivative of Verhoeff check digit algorithm.
+Python port of alphanumeric derivative of Verhoeff check digit algorithm.
 
 Ported from: https://gist.github.com/mwgamera/1088656
 """

diff --git a/verhoeff_alpha.py b/verhoeff_alpha.py
@@ -0,0 +1,124 @@
+#!/usr/bin/env python
+
+"""
+Python derivative of alphanumeric derivative of Verhoeff check digit algorithm.
+
+Ported from: https://gist.github.com/mwgamera/1088656
+"""
+
+N  = 18
+N2 = N * 2
+
+class Verhoeff(object):
+
+    def __init__(self):
+
+        # Multiplication table
+        self.d18_op = [0 for i in xrange(N2*N2)]
+        for i in xrange(N):
+            for j in xrange(N):
+                self.d18_op[N2*i+j] = (i + j) % N
+        for i in xrange(N):
+            for j in xrange(N, N2):
+                self.d18_op[N2*i+j] = N + (i + j) % N
+        for i in xrange(N, N2):
+            for j in xrange(N):
+                self.d18_op[N2*i+j] = N + (i - j) % N
+        for i in xrange(N, N2):
+            for j in xrange(N, N2):
+                self.d18_op[N2*i+j] = (N + i - j) % N
+
+        # Inverse table
+        self.d18_inv = [0 for i in xrange(N2)]
+        for i in xrange(1, N):
+            self.d18_inv[i] = N - i
+        for i in xrange(N, N2):
+            self.d18_inv[i] = i
+
+        # Permutation table
+        self.perm = [[] for i in xrange(N2)]
+        p = [29,0,32,11,35,20,7,27,2,4,19,28,30,1,5,12,3,9,16,
+             22,6,33,8,24,26,21,14,10,34,31,15,25,17,13,23,18]
+        b = [False for i in xrange(len(p))]
+        i = 0
+        while i < len(b):
+            h = [None]
+            c = h
+            ln = 0
+            while not b[i]:
+                cc = [None, p[i]]
+                c[0] = cc
+                c = cc
+                b[i] = True
+                i = p[i]
+                ln += 1
+            c[0] = h[0]
+            for j in xrange(ln):
+                pp = [0 for x in xrange(ln)]
+                self.perm[c[1]] = pp
+                for k in xrange(ln):
+                    pp[k] = c[1]
+                    c = c[0]
+                c = c[0]
+            while i < len(b) and b[i] == True:
+                i += 1
+
+        # Alphanumeric to numeric conversion table
+        self.a2i = [0xff for i in xrange(256)]
+        for i in xrange(0x30, 0x3a): self.a2i[i] = i - 0x30
+        for i in xrange(0x41, 0x5b): self.a2i[i] = i - 0x41 + 10
+        for i in xrange(0x61, 0x7b): self.a2i[i] = i - 0x61 + 10
+
+        # Numeric to alphanumeric conversion table
+        self.i2a = [0 for i in xrange(N2)]
+        for i in xrange(0, 10):  self.i2a[i] = i + 0x30
+        for i in xrange(10, N2): self.i2a[i] = i + 0x41 - 10
+
+    def op(self, i, j):
+        """ Group operation """
+        return self.d18_op[N2*i+j]
+
+    def nperm(self, i , n):
+        """ Compute n-th application of the permutation """
+        return self.perm[i][n % len(self.perm[i])]
+
+    def is_valid(self, s):
+        return self.verify(s) == 0
+
+    def verify(self, s):
+        """ Verify correctness of check digit, returns 0 if correct """
+        i = 0
+        c = 0
+        for ch in reversed(s):
+            ch = self.a2i[ord(ch) & 0xff]
+            if ch != 0xff:
+                c = self.op(c, self.nperm(ch, i))
+                i += 1
+        return c
+
+    def create(self, s):
+        """ Create a new check digit """
+        i = 1
+        c = 0
+        for ch in reversed(s):
+            ch = self.a2i[ord(ch) & 0xff]
+            if ch != 0xff:
+                c = self.op(c, self.nperm(ch, i))
+                i += 1
+        return self.i2a[self.d18_inv[c]]
+
+    def append(self, s):
+        """ Append check digit to the given string """
+        return s + chr(self.create(s))
+
+def main():
+
+    v = Verhoeff()
+    assert v.create('ABCDEF') == 67
+    assert v.append('123ABCDEF') == '123ABCDEFD'
+    assert v.append('ABCDEF')    == 'ABCDEFC'
+
+    assert v.verify('ABCDEFC')   == 0
+
+if __name__ == '__main__':
+    main()
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