diff -r 0135e64c6c66 -r c4fd2813b127 rust/hwphysics/src/common.rs
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/rust/hwphysics/src/common.rs	Wed Jul 31 23:14:27 2019 +0200
@@ -0,0 +1,69 @@
+use fpnum::{fp, FPNum};
+use std::{collections::BinaryHeap, num::NonZeroU16, ops::Add};
+
+pub type GearId = NonZeroU16;
+pub trait GearData {}
+
+#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Copy, Debug)]
+pub struct Millis(u32);
+
+impl Millis {
+    #[inline]
+    pub fn new(value: u32) -> Self {
+        Self(value)
+    }
+
+    #[inline]
+    pub fn get(self) -> u32 {
+        self.0
+    }
+
+    #[inline]
+    pub fn to_fixed(self) -> FPNum {
+        FPNum::new(self.0 as i32, 1000)
+    }
+}
+
+impl Add for Millis {
+    type Output = Self;
+
+    fn add(self, rhs: Self) -> Self::Output {
+        Self(self.0 + rhs.0)
+    }
+}
+
+pub trait GearDataProcessor<T: GearData> {
+    fn add(&mut self, gear_id: GearId, gear_data: T);
+    fn remove(&mut self, gear_id: GearId);
+}
+
+pub trait GearDataAggregator<T: GearData> {
+    fn find_processor(&mut self) -> &mut GearDataProcessor<T>;
+}
+
+pub struct GearAllocator {
+    max_id: u16,
+    free_ids: BinaryHeap<GearId>,
+}
+
+impl GearAllocator {
+    pub fn new() -> Self {
+        Self {
+            max_id: 0,
+            free_ids: BinaryHeap::with_capacity(1024),
+        }
+    }
+
+    pub fn alloc(&mut self) -> Option<GearId> {
+        self.free_ids.pop().or_else(|| {
+            self.max_id.checked_add(1).and_then(|new_max_id| {
+                self.max_id = new_max_id;
+                NonZeroU16::new(new_max_id)
+            })
+        })
+    }
+
+    pub fn free(&mut self, gear_id: GearId) {
+        self.free_ids.push(gear_id)
+    }
+}