iidxhook9: Add turntable multiplier

src/main/util/Module.mk

@@ -10,6 +10,7 @@ src_util        := \
     iobuf.c \
     list.c \
     log.c \
+    math.c \
     mem.c \
     msg-thread.c \
     net.c \

src/main/util/math.c

@@ -0,0 +1,22 @@
+#include "util/math.h"
+
+int16_t get_wrapped_delta_s16(int16_t val, int16_t last, int16_t bound) {
+    int16_t half_point = bound / 2;
+
+    int16_t delta = val - last;
+
+    if (delta > half_point) {
+        delta -= bound;
+    }
+
+    if (delta < -half_point) {
+        delta += bound;
+    }
+
+    // delta is now between (-half_point - half_point)
+    return delta;
+}
+
+int16_t sign_s16(int16_t x) {
+    return (x > 0) - (x < 0);
+}

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