iidxhook9: Add turntable multiplier

src/main/util/math.h

@@ -0,0 +1,9 @@
+#ifndef UTIL_MATH_H
+#define UTIL_MATH_H
+
+#include <stdint.h>
+
+int16_t get_wrapped_delta_s16(int16_t val, int16_t last, int16_t bound);
+int16_t sign_s16(int16_t x);
+
+#endif