Add Pages and Bytes newtypes

lib/runtime-core/src/units.rs

@@ -0,0 +1,94 @@
+use std::{
+    fmt,
+    ops::{Add, Sub},
+};
+
+const WASM_PAGE_SIZE: usize = 65_536;
+const WASM_MAX_PAGES: usize = 65_536;
+
+/// Units of WebAssembly pages (as specified to be 65,536 bytes).
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
+pub struct Pages(pub u32);
+
+impl Pages {
+    pub fn checked_add(self, rhs: Pages) -> Option<Pages> {
+        let added = (self.0 as usize) + (rhs.0 as usize);
+        if added <= WASM_MAX_PAGES {
+            Some(Pages(added as u32))
+        } else {
+            None
+        }
+    }
+
+    pub fn bytes(self) -> Bytes {
+        self.into()
+    }
+}
+
+impl fmt::Debug for Pages {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{} pages", self.0)
+    }
+}
+
+/// Units of WebAssembly memory in terms of 8-bit bytes.
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
+pub struct Bytes(pub usize);
+
+impl fmt::Debug for Bytes {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{} bytes", self.0)
+    }
+}
+
+impl From<Pages> for Bytes {
+    fn from(pages: Pages) -> Bytes {
+        Bytes((pages.0 as usize) * WASM_PAGE_SIZE)
+    }
+}
+
+impl<T> Sub<T> for Pages
+where
+    T: Into<Pages>,
+{
+    type Output = Pages;
+    fn sub(self, rhs: T) -> Pages {
+        Pages(self.0 - rhs.into().0)
+    }
+}
+
+impl<T> Add<T> for Pages
+where
+    T: Into<Pages>,
+{
+    type Output = Pages;
+    fn add(self, rhs: T) -> Pages {
+        Pages(self.0 + rhs.into().0)
+    }
+}
+
+impl From<Bytes> for Pages {
+    fn from(bytes: Bytes) -> Pages {
+        Pages((bytes.0 / WASM_PAGE_SIZE) as u32)
+    }
+}
+
+impl<T> Sub<T> for Bytes
+where
+    T: Into<Bytes>,
+{
+    type Output = Bytes;
+    fn sub(self, rhs: T) -> Bytes {
+        Bytes(self.0 - rhs.into().0)
+    }
+}
+
+impl<T> Add<T> for Bytes
+where
+    T: Into<Bytes>,
+{
+    type Output = Bytes;
+    fn add(self, rhs: T) -> Bytes {
+        Bytes(self.0 + rhs.into().0)
+    }
+}