impl 32 bit backend

src/backend.rs

@@ -1,4 +1,5 @@
 use sptr::Strict;
+use std::mem;
 
 pub trait Backend<T> {
     type Stored: Copy;
@@ -10,6 +11,20 @@ pub trait Backend<T> {
     fn get_int(s: Self::Stored) -> Self;
 }
 
+#[allow(clippy::should_assert_eq, dead_code)] // :/
+const fn assert_size<B>()
+where
+    B: Backend<()>,
+{
+    let has_equal_size = mem::size_of::<B>() == mem::size_of::<B::Stored>();
+    assert!(has_equal_size);
+}
+
+#[cfg(not(target_pointer_width = "16"))]
+const _: () = assert_size::<u128>();
+const _: () = assert_size::<u64>();
+const _: () = assert_size::<usize>();
+
 impl<T> Backend<T> for usize {
     type Stored = *mut T;
 
@@ -44,24 +59,75 @@ impl<T> Backend<T> for u64 {
     }
 }
 
-#[cfg(target_pointer_width = "64")]
-impl<T> Backend<T> for u128 {
-    // this one keeps the MSB in the pointer address, and the LSB in the integer
+macro_rules! impl_backend_2_tuple {
+    (impl for $ty:ty { (*mut T, $int:ident), $num:literal }) => {
+        impl<T> Backend<T> for $ty {
+            // this one keeps the MSB in the pointer address, and the LSB in the integer
 
-    type Stored = (*mut T, u64);
+            type Stored = (*mut T, $int);
 
-    fn get_ptr(s: Self::Stored) -> (*mut T, Self) {
-        (s.0, Self::get_int(s))
-    }
+            fn get_ptr(s: Self::Stored) -> (*mut T, Self) {
+                (s.0, Self::get_int(s))
+            }
 
-    fn set_ptr(provenance: *mut T, addr: Self) -> Self::Stored {
-        let ptr_addr = (addr >> 64) as u64;
-        let int_addr = addr as u64; // truncate it
-        (Strict::with_addr(provenance, ptr_addr as usize), int_addr)
-    }
+            fn set_ptr(provenance: *mut T, addr: Self) -> Self::Stored {
+                let ptr_addr = (addr >> $num) as usize;
+                let int_addr = addr as $int; // truncate it
+                (Strict::with_addr(provenance, ptr_addr), int_addr)
+            }
 
-    fn get_int(s: Self::Stored) -> Self {
-        let ptr_addr = Strict::addr(s.0) as u64;
-        (u128::from(ptr_addr) << 64) | u128::from(s.1)
-    }
+            fn get_int(s: Self::Stored) -> Self {
+                let ptr_addr = Strict::addr(s.0) as $int;
+                (<$ty>::from(ptr_addr) << $num) | <$ty>::from(s.1)
+            }
+        }
+    };
 }
+
+/// num1 is ptr-sized, num2 is 2*ptr sized
+#[cfg_attr(target_pointer_width = "64", allow(unused))] // not required on 64 bit
+macro_rules! impl_backend_3_tuple {
+    (impl for $ty:ty { (*mut T, $int1:ident, $int2:ident), $num1:literal, $num2:literal }) => {
+        impl<T> Backend<T> for $ty {
+            // this one keeps the MSB in the pointer address, ISB in int1 and the LSB in the int2
+
+            type Stored = (*mut T, $int1, $int2);
+
+            fn get_ptr(s: Self::Stored) -> (*mut T, Self) {
+                (s.0, Self::get_int(s))
+            }
+
+            fn set_ptr(provenance: *mut T, addr: Self) -> Self::Stored {
+                let ptr_addr = (addr >> ($num1 + $num2)) as usize;
+                let num1_addr = (addr >> $num2) as $int1; // truncate it
+                let num2_addr = addr as $int2; // truncate it
+                (
+                    Strict::with_addr(provenance, ptr_addr),
+                    num1_addr,
+                    num2_addr,
+                )
+            }
+
+            fn get_int(s: Self::Stored) -> Self {
+                let ptr_addr = Strict::addr(s.0) as $ty;
+                let num1_addr = self.1 as $ty;
+                let num2_addr = self.2 as $ty;
+                (ptr_addr << ($num1 + $num2)) | (num1_addr << ($num2)) | num2_addr
+            }
+        }
+    };
+}
+
+#[cfg(target_pointer_width = "64")]
+impl_backend_2_tuple!(impl for u128 { (*mut T, u64), 64 });
+
+#[cfg(target_pointer_width = "32")]
+impl_backend_2_tuple!(impl for u64 { (*mut T, u32), 32 });
+
+#[cfg(target_pointer_width = "32")]
+impl_backend_3_tuple!(impl 128 u64 { (*mut T, u32, u64), 32, 64 });
+
+#[cfg(target_pointer_width = "16")]
+impl_backend_3_tuple!(impl for u64 { (*mut T, u16, u32), 16, 32 });
+
+// no 128 on 16 bit for now