Add pre-commit script

pre-commit

@@ -0,0 +1,27 @@
+#!/bin/sh -e
+#
+# An example hook script to verify what is about to be committed.
+# Called by "git commit" with no arguments.  The hook should
+# exit with non-zero status after issuing an appropriate message if
+# it wants to stop the commit.
+#
+
+CLANGFORMATDIFF=`git config --get clangformatdiff.binary`
+
+if [ -z "$CLANGFORMATDIFF" ]; then
+    CLANGFORMATDIFF=clang-format-diff.py
+fi
+
+errors=`git diff-index --cached --diff-filter=ACMR -p HEAD -- | $CLANGFORMATDIFF -p1`
+
+if [ -n "$errors" ]; then
+    echo "$errors"
+    echo "--"
+    echo "[ERROR] We have detected the difference between the code to commit"
+    echo "and clang-format style rules.  Please fix this problem in either:"
+    echo "1) Apply patch above."
+    echo "2) Use clang-format to format lines."
+    echo "3) Reformat these lines manually."
+    echo "Aborting commit."
+    exit 1
+fi