implement DJN

1 files changed, 20 insertions, 0 deletions

diff --git a/src/vm/instruction.js b/src/vm/instruction.js
index f323f84..c235b9a 100644
--- a/src/vm/instruction.js
+++ b/src/vm/instruction.js
@@ -142,3 +142,23 @@ exports.JMN = function(core, pc, ins) {
 		return [core.normalize(pc, 1)];
 	}
 }
+
+
+exports.DJN = function(core, pc, ins) {
+	let test;
+
+	if (ins.b.mode === AddrMode.Immediate) {
+		ins.b.value -= 1;
+		test = (ins.b.value !== 0);
+	} else {
+		const src = core.getValue(pc, ins.b);
+		src.b.value -= 1;
+		test = (src.b.value !== 0);
+	}
+
+	if (test) {
+		return [core.getLocation(pc, ins.a)];
+	} else {
+		return [core.normalize(pc, 1)];
+	}
+}