fix operand resolution to match specmain

1 files changed, 15 insertions, 0 deletions

diff --git a/src/vm/instruction.test.js b/src/vm/instruction.test.js
index cf23404..279b9b8 100644
--- a/src/vm/instruction.test.js
+++ b/src/vm/instruction.test.js
@@ -393,6 +393,21 @@ test('JMP correctly jumps', () => {
 });
 
 
+test('JMP correctly responds to B-field predecrement', () => {
+	const core = new Core(CORESIZE);
+	const pc = 2;
+	core.data[pc] = {
+		opcode: 'JMP',
+		a: { mode: 'direct', value: -3 },
+		b: { mode: 'predecrement', value: 1 },
+	};
+	const ins = core.data[pc];
+
+	expect(JMP(core, pc, ins)).toEqual([CORESIZE-1]);
+	expect(core.data[pc+1].b.value).toBe(-1);
+});
+
+
 test('JMZ correctly jumps in non-immediate mode', () => {
 	const core = new Core(CORESIZE);
 	const pc = 2;