add (cas), (casXX), and (bfcas)

crsn_buf/src/defs.rs

@@ -45,6 +45,7 @@ pub enum BufOps {
     Write { obj: RdObj, idx: Rd, value: Rd },
     Insert { obj: RdObj, idx: Rd, value: Rd },
     Remove { dst: Wr, obj: RdObj, idx: Rd },
+    CompareSwap { obj: RdObj, idx: Rd, expected: Rd, src: Rd },
 
     // Whole buffer ops
     Resize { obj: RdObj, len: Rd },

crsn_buf/src/exec.rs

@@ -138,6 +138,33 @@ impl OpTrait for BufOps {
                 }
             }
 
+            BufOps::CompareSwap { obj, idx, expected, src } => {
+                state.clear_status();
+                let handle = state.read_obj(obj)?;
+                let idx = state.read(idx)? as usize;
+                let expected = state.read(expected)?;
+                let store: &mut ExtData = state.ext_mut();
+                let buf = store.buffers.get_mut(&handle).ok_or_else(|| Fault::ObjectNotExist(handle))?;
+                if idx < buf.data.len() {
+                    if buf.data[idx] == expected {
+                        // This looks stupid and it is stupid - the dance is needed to satisfy the borrow checker.
+                        let val = state.read(src)?;
+                        let store: &mut ExtData = state.ext_mut();
+                        let buf = store.buffers.get_mut(&handle).unwrap();
+                        buf.data[idx] = val;
+                        state.set_flag(Flag::Equal, true);
+                    }
+                } else if idx == buf.data.len() && expected == 0 {
+                    let val = state.read(src)?;
+                    let store: &mut ExtData = state.ext_mut();
+                    let buf = store.buffers.get_mut(&handle).unwrap();
+                    buf.data.push_back(val);
+                    state.set_flag(Flag::Equal, true);
+                } else {
+                    state.set_flag(Flag::Overflow, true);
+                }
+            }
+
             BufOps::Insert { obj, idx, value } => {
                 state.clear_status();
                 let handle = state.read_obj(obj)?;
@@ -255,6 +282,10 @@ impl OpTrait for BufOps {
                 sexp::list(&[A("bfwr"), A(obj), A(idx), A(value)])
             }
 
+            BufOps::CompareSwap { obj, idx, expected , src } => {
+                sexp::list(&[A("bfcas"), A(obj), A(idx), A(expected), A(src)])
+            }
+
             BufOps::Insert { obj, idx, value } => {
                 sexp::list(&[A("bfins"), A(obj), A(idx), A(value)])
             }

crsn_buf/src/parse.rs

@@ -75,6 +75,14 @@ pub(crate) fn parse<'a>(_pos: &SourcePosition, keyword: &str, mut args: TokenPar
             BufOps::Write { obj, idx, value }
         }
 
+        "bfcas" => {
+            let obj = args.next_rdobj()?;
+            let idx = args.next_rd()?;
+            let expected = args.next_rd()?;
+            let src = args.next_rd()?;
+            BufOps::CompareSwap { obj, idx, expected, src }
+        }
+
         "bfsz" => {
             let dst = args.next_wr()?;
             let obj = args.next_rdobj()?;