object

runtime/rust/src/defs.rs

@@ -8,3 +8,12 @@ pub type Pointer = Word;
 
 pub const INITIAL_STACK_CAPACITY: usize = 1024;
 pub const INITIAL_MEMORY_CAPACITY: usize = 1024;
+pub const OBJECT_HEADER_SIZE: usize = 1;
+
+pub fn to_usize(s: Word) -> usize {
+    s as usize
+}
+
+pub fn to_word(s: usize) -> Word {
+    s as Word
+}

runtime/rust/src/lib.rs

@@ -1,5 +1,6 @@
 pub mod defs;
 pub mod memory;
+pub mod object;
 pub mod stack;
 
 pub fn add(left: usize, right: usize) -> usize {

runtime/rust/src/object.rs

@@ -0,0 +1,39 @@
+// Object access and manipulation
+
+use super::defs::*;
+use super::memory::*;
+
+const UID_SHIFT: usize = 0;
+const UID_MASK: Word = 0xff;
+const NFIELDS_SHIFT: usize = 8;
+const NFIELDS_MASK: Word = 0xffffff;
+
+pub fn get_header_uid(h: Word) -> Word {
+    (h >> UID_SHIFT) & UID_MASK
+}
+
+pub fn get_header_nfields(h: Word) -> usize {
+    to_usize((h >> NFIELDS_SHIFT) & NFIELDS_MASK)
+}
+
+pub fn make_header(uid: Word, nfields: usize) -> Word {
+    (uid << UID_SHIFT) | (to_word(nfields) << NFIELDS_SHIFT)
+}
+
+impl Memory {
+    pub fn get_header(self: &Memory, ptr: Pointer) -> Word {
+        self[to_usize(ptr)]
+    }
+
+    pub fn get_field(self: &Memory, ptr: Pointer, idx: Word) -> Word {
+        self[to_usize(ptr) + OBJECT_HEADER_SIZE + to_usize(idx)]
+    }
+
+    pub fn get_uid(self: &Memory, ptr: Pointer) -> Word {
+        get_header_uid(self.get_header(ptr))
+    }
+
+    pub fn get_nfields(self: &Memory, ptr: Pointer) -> usize {
+        get_header_nfields(self.get_header(ptr))
+    }
+}