I should probably make more commits

src/utils.rs

@@ -0,0 +1,26 @@
+pub fn load_u16_le(bytes: &[u8]) -> u16 {
+    assert_eq!(bytes.len(), 2);
+
+    u16::from_le_bytes(bytes.try_into().unwrap())
+}
+pub fn load_u32_le(bytes: &[u8]) -> u32 {
+    assert_eq!(bytes.len(), 4);
+
+    u32::from_le_bytes(bytes.try_into().unwrap())
+}
+
+/// replace the value at x with f(x)
+///
+/// SAFETY:
+/// should be safe, I guess? MIRI didn't complain about it
+pub fn replace<T>(x: &mut T, f: impl FnOnce(T) -> T) {
+    unsafe {
+        let x_ptr = x as *mut T;
+
+        let old_x = std::ptr::read(x_ptr);
+
+        let new_x = f(old_x);
+
+        std::ptr::write(x_ptr, new_x);
+    }
+}