diff --git a/debug.h b/debug.h
new file mode 100644
index 0000000..90a10e5
--- /dev/null
+++ b/debug.h
@@ -0,0 +1,20 @@
+#include <features.h>
+
+void debug_(int level, char *file, int line, char *func, char *fmt, ...);
+
+# define debug(level, expr...) debug_(level, __FILE__, __LINE__, DEBUG_FUNCTION, expr)
+
+/* Version 2.4 and later of GCC define a magical variable `__PRETTY_FUNCTION__'
+   which contains the name of the function currently being defined.
+   This is broken in G++ before version 2.6.
+   C9x has a similar variable called __func__, but prefer the GCC one since
+   it demangles C++ function names.  */
+# if __GNUC_PREREQ (2, 4)
+#   define DEBUG_FUNCTION	__PRETTY_FUNCTION__
+# else
+#  if defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L
+#   define DEBUG_FUNCTION	__func__
+#  else
+#   define DEBUG_FUNCTION	((__const char *) 0)
+#  endif
+# endif