Implement SUBN instruction.

1 files changed, 9 insertions, 1 deletions

diff --git a/asm.myr b/asm.myr
index ab26cbb..9dcde13 100644
--- a/asm.myr
+++ b/asm.myr
@@ -221,7 +221,15 @@ const emitinstr = {p
         | _:
             -> `std.Err(std.fmt("invalid argument to SUB: {}", p[1]))
         ;;
-
+    | "SUBN":
+        if p.len < 3
+            -> `std.Err("SUBN missing arguments")
+        ;;
+        match (parselit(p[1]), parselit(p[2]))
+        | (`Register(m), `Register(n)): b = `std.Some([0x80 | (m & 0x0f), ((n & 0x0f) << 1) | 0x07])
+        | _:
+            -> `std.Err(std.fmt("invalid argument to SUBN: {}", p[1]))
+        ;;
     | _:
         -> `std.Err(std.fmt("unrecognized instruction {}", p[0]))
     ;;