1 files changed, 57 insertions, 0 deletions

diff --git a/src/reducer/validation_DE_TIN.c b/src/reducer/validation_DE_TIN.c
new file mode 100644
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--- /dev/null
+++ b/src/reducer/validation_DE_TIN.c
@@ -0,0 +1,57 @@
+/*
+  This file is part of Anastasis
+  Copyright (C) 2020, 2021 Taler Systems SA
+
+  Anastasis is free software; you can redistribute it and/or modify it under the
+  terms of the GNU Lesser General Public License as published by the Free Software
+  Foundation; either version 3, or (at your option) any later version.
+
+  Anastasis is distributed in the hope that it will be useful, but WITHOUT ANY
+  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+  A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License along with
+  Anastasis; see the file COPYING.GPL.  If not, see <http://www.gnu.org/licenses/>
+*/
+/**
+ * @file redux/validation_DE_TIN.c
+ * @brief validation logic for German taxpayer identification numbers
+ * @author Christian Grothoff
+ */
+#include <string.h>
+#include <stdbool.h>
+
+
+/**
+ * Function to validate a German Taxpayer identification number.
+ *
+ * See https://de.wikipedia.org/wiki/Steuerliche_Identifikationsnummer
+ * for the structure!
+ *
+ * @param tin_number tax number to validate (input)
+ * @return true if validation passed, else false
+ */
+bool
+DE_TIN_check (const char *tin_number)
+{
+  unsigned int csum;
+  unsigned int product = 10;
+
+  if (strlen (tin_number) != 11)
+    return false;
+  for (unsigned int i = 0; i<10; i++)
+  {
+    unsigned int sum = ((tin_number[i] - '0') + product) % 10;
+    if (0 == sum)
+      sum = 10;
+    product = sum * 2 % 11;
+  }
+  csum = 11 - product;
+  if (10 == csum)
+    csum = 0;
+  if (tin_number[10] != '0' + csum)
+    return false;
+  if (tin_number[0] == '0')
+    return false;
+  return true;
+}