Initial import

diff --git a/acpi_table_checksum.py b/acpi_table_checksum.py
new file mode 100755 (executable)
index 0000000..999ee32
--- /dev/null
+++ b/acpi_table_checksum.py
@@ -0,0 +1,61 @@
+#!/usr/bin/env python
+#
+# acpi_table_checksum - verify and calculate the checksum of ACPI tables
+#
+# Copyright (C) 2015  Antonio Ospite <ao2@ao2.it>
+#
+# This program is free software. It comes without any warranty, to
+# the extent permitted by applicable law. You can redistribute it
+# and/or modify it under the terms of the Do What The Fuck You Want
+# To Public License, Version 2, as published by Sam Hocevar. See
+# http://sam.zoy.org/wtfpl/COPYING for more details.
+
+import sys
+
+CHECKSUM_OFFSET = 9
+
+
+# Two's complement byte checksum:
+def acpi_table_checksum(buf, length):
+    checksum = 0
+
+    for i in range(0, length):
+        checksum = (checksum + buf[i]) & 0xff
+
+    return (0x100 - checksum) & 0xff
+
+
+def calc_new_checksum(data):
+    data_copy = data[:]
+    data_copy[CHECKSUM_OFFSET] = 0
+    return acpi_table_checksum(data_copy, len(data_copy))
+
+
+def verify_checksum(data):
+    return (acpi_table_checksum(data, len(data)) == 0)
+
+
+def usage():
+    print "%s <ACPI_TABLE>" % sys.argv[0]
+
+
+if __name__ == "__main__":
+    if len(sys.argv) != 2:
+        usage()
+        sys.exit(1)
+
+    table = sys.argv[1]
+
+    with open(table, 'rb') as f:
+        data = bytearray(f.read())
+
+        checksum_is_valid = verify_checksum(data)
+
+        if checksum_is_valid:
+            print "Checksum valid (0x%02x)." % data[CHECKSUM_OFFSET]
+        else:
+            print "Checksum not valid, calculating a new one..."
+            new_checksum = calc_new_checksum(data)
+            print "New checksum 0x%02x" % new_checksum
+            data[CHECKSUM_OFFSET] = new_checksum
+            print "Checksum vaiid %d" % verify_checksum(data)