add get_opcode and its test, fix a couple bugs + semantics things

twasm/asm/tests.asm

@@ -37,6 +37,9 @@ run_tests:
   call clear_test_arena
   call test_get_direct_addressing_ModRM
 
+  call clear_test_arena
+  call test_get_opcode
+
   ret
   .msg db "running test suite...", 0x0A, 0x00
 
@@ -513,6 +516,47 @@ test_get_direct_addressing_ModRM:
     ret
   .msg db "test_get_direct_addressing_ModRM...", 0x00
 
+; ------------------------------------------------------------------------------
+; test_get_opcode
+;
+; description:
+; tests get_opcode described functionality
+; ------------------------------------------------------------------------------
+
+test_get_opcode:
+  mov rsi, .msg
+  call print
+
+  mov di, 0x0053 ; xor
+  call get_opcode
+  cmp al, 0x33
+  jne .fail
+
+  mov di, 0x0054  ; inc
+  call get_opcode
+  cmp al, 0xFF
+  jne .fail
+
+  mov di, 0x004F  ; hlt
+  call get_opcode
+  cmp al, 0xF4
+  jne .fail
+
+  mov di, 0x0003  ; rdx (not an operator)
+  call get_opcode
+  cmp al, UNRECOGNISED_ID_OPCODE
+  jne .fail
+
+  .pass:
+    mov rsi, msg_pass
+    call print
+    ret
+  .fail:
+    mov rsi, msg_fail
+    call print
+    ret
+  .msg db "test_get_opcode...", 0x00
+
 msg_pass:
   db 0x0A
   times (TEST_LINE_LENGTH + .start - .end) db " ", ; right align