integer overflow/underflow stuff

math.c

@@ -99,3 +99,40 @@ fn Vec2f32 vec2FromHexCube(Vec2 map_center, XYZ cube, f32 size, f32 border_thick
   };
 }
 
+/* from https://graphitemaster.github.io/aau/
+T midpoint(T x, T y) {
+    // U is the unsigned version of your type T, or same as T if T already unsigned
+    // digits is the number of numeric digits (not including sign) in your type T.
+    // std::numeric_limits<T>::digits in C++ is helpful here.
+    U shift = digits - 1;
+    U difference = (U)x - (U)y;
+    U sign = y < x;
+    U half = (difference / 2) + (sign << shift) + (sign & difference);
+    T mid = (T)(x + half);
+    return mid;
+}
+ */
+
+fn i32 i32Middle(i32 x, i32 y) {
+  u32 shift = 31 - 1;
+  u32 difference = (u32)x - (u32)y;
+  u32 sign = y < x;
+  u32 half = (difference / 2) + (sign << shift) + (sign & difference);
+  i32 mid = (i32)(x + half);
+  return mid;
+}
+
+fn u32 u32Middle(u32 x, u32 y) {
+  u32 shift = 32 - 1;
+  u32 difference = (u32)x - (u32)y;
+  u32 sign = y < x;
+  u32 half = (difference / 2) + (sign << shift) + (sign & difference);
+  u32 mid = (u32)(x + half);
+  return mid;
+}
+
+fn u64 u64SafeMul(u64 x, u64 y) {
+  assert(!(y && x > MAX_u64/y));
+  return x * y;
+}
+