Add ADD, DEC, TEST, RET instructions

1 files changed, 22 insertions, 2 deletions

diff --git a/src/lib.rs b/src/lib.rs
index e38da14..27164ad 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -107,8 +107,8 @@ impl Asm {
         Self: EncodeRI<T>,
     {
         // MI operand encoding.
-        //   op1 -> modrm.rm
-        //   op2 -> modrm.reg
+        //   op1           -> modrm.rm
+        //   opc extension -> modrm.reg
         let modrm = modrm(
             0b11,      /* mod */
             opc_ext,   /* reg */
@@ -123,6 +123,26 @@ impl Asm {
         self.emit(op2.bytes());
     }
 
+    fn encode_r<T: Reg>(&mut self, opc: u8, opc_ext: u8, op1: T)
+    where
+        Self: EncodeRI<T>,
+    {
+        // M operand encoding.
+        //   op1           -> modrm.rm
+        //   opc extension -> modrm.reg
+        let modrm = modrm(
+            0b11,      /* mod */
+            opc_ext,   /* reg */
+            op1.idx(), /* rm */
+        );
+
+        let prefix = <Self as EncodeRI<T>>::legacy_prefix();
+        let rex = <Self as EncodeRI<T>>::rex(op1);
+
+        self.emit_optional(&[prefix, rex]);
+        self.emit(&[opc, modrm]);
+    }
+
     fn encode_mr<T: Reg>(&mut self, opc: u8, op1: MemOp, op2: T)
     where
         Self: EncodeMR<T>,