3 files changed, 68 insertions, 13 deletions

diff --git a/src/vm/core.js b/src/vm/core.js
index 6303ee5..9b0fe77 100644
--- a/src/vm/core.js
+++ b/src/vm/core.js
@@ -19,7 +19,12 @@ class Core {
 
 
 	normalize(pc, value) {
-		return (pc + value) % this.data.length;
+		const v = (pc + value) % this.data.length;
+		if (v < 0) {
+			return v + this.data.length;
+		} else {
+			return v;
+		}
 	}
 
 
diff --git a/src/vm/instruction.js b/src/vm/instruction.js
index a79427b..878d20b 100644
--- a/src/vm/instruction.js
+++ b/src/vm/instruction.js
@@ -20,7 +20,7 @@ exports.MOV = function(core, pc, ins) {
 		core.data[dstLocation] = JSON.parse(JSON.stringify(src));
 	}
 
-	return [pc + 1];
+	return [core.normalize(pc, 1)];
 }
 
 
@@ -35,7 +35,7 @@ exports.ADD = function(core, pc, ins) {
 		dst.b.value += src.b.value;
 	}
 
-	return [pc + 1];
+	return [core.normalize(pc, 1)];
 }
 
 
@@ -50,7 +50,7 @@ exports.SUB = function(core, pc, ins) {
 		dst.b.value -= src.b.value;
 	}
 
-	return [pc + 1];
+	return [core.normalize(pc, 1)];
 }
 
 
@@ -58,9 +58,9 @@ exports.CMP = function(core, pc, ins) {
 	if (ins.a.mode === AddrMode.Immediate) {
 		const test = core.getValue(pc, ins.b);
 		if (test.b.value === ins.a.value) {
-			return [pc + 2];
+			return [core.normalize(pc, 2)];
 		} else {
-			return [pc + 1];
+			return [core.normalize(pc, 1)];
 		}
 	} else {
 		const left = core.getValue(pc, ins.a);
@@ -75,9 +75,9 @@ exports.CMP = function(core, pc, ins) {
 			left.b.mode  === right.b.mode  &&
 			left.b.value === right.b.value
 		) {
-			return [pc + 2];
+			return [core.normalize(pc, 2)];
 		} else {
-			return [pc + 1];
+			return [core.normalize(pc, 1)];
 		}
 	}
 }
@@ -87,17 +87,23 @@ exports.SLT = function(core, pc, ins) {
 	if (ins.a.mode === AddrMode.Immediate) {
 		const test = core.getValue(pc, ins.b);
 		if (ins.a.value < test.b.value) {
-			return [pc + 2];
+			return [core.normalize(pc, 2)];
 		} else {
-			return [pc + 1];
+			return [core.normalize(pc, 1)];
 		}
 	} else {
 		const left = core.getValue(pc, ins.a);
 		const right = core.getValue(pc, ins.b);
 		if (left.b.value < right.b.value) {
-			return [pc + 2];
+			return [core.normalize(pc, 2)];
 		} else {
-			return [pc + 1];
+			return [core.normalize(pc, 1)];
 		}
 	}
 }
+
+
+exports.JMP = function(core, pc, ins) {
+	const dstLoc = core.getLocation(pc, ins.a);
+	return [dstLoc];
+}
diff --git a/src/vm/instruction.test.js b/src/vm/instruction.test.js
index a93a3b0..8efa47f 100644
--- a/src/vm/instruction.test.js
+++ b/src/vm/instruction.test.js
@@ -1,7 +1,11 @@
 'use strict';
 
 const { Core } = require('./core.js');
-const { DAT, MOV, ADD, SUB, CMP, SLT } = require('./instruction.js');
+const { 
+	DAT, 
+	MOV, ADD, SUB, CMP, SLT,
+	JMP,
+} = require('./instruction.js');
 
 
 const CORESIZE = 8000;
@@ -109,6 +113,33 @@ test('MOV correctly handles predecrement indirection', () => {
 });
 
 
+test('MOV correctly handles core boundaries', () => {
+	const core = new Core(CORESIZE);
+	const pc = CORESIZE-1;
+	core.data[pc] = {
+		opcode: 'MOV',
+		a: { mode: 'immediate', value: 100 },
+		b: { mode: 'predecrement', value: 2 },
+	};
+	const ins = core.data[pc];
+	expect(core.data[0].opcode).toBe('DAT');
+	expect(MOV(core, pc, ins)).toEqual([0]);
+	expect(core.data[1]).toEqual({	
+		opcode: 'DAT',
+		a: { mode: 'immediate', value: 0 },
+		b: { mode: 'immediate', value: -1 },
+	});
+
+	expect(core.data[0]).toEqual({	
+		opcode: 'DAT',
+		a: { mode: 'immediate', value: 0 },
+		b: { mode: 'immediate', value: 100 },
+	});
+
+});
+
+
+
 test('ADD correctly adds two full instructions', () => {
 	const core = new Core(CORESIZE);
 	const pc = 20;
@@ -347,3 +378,16 @@ test('SLT properly compares B-fields', () => {
 	expect(SLT(core, pc, ins)).toEqual([pc+2]);
 });
 
+
+test('JMP correctly jumps', () => {
+	const core = new Core(CORESIZE);
+	const pc = 2;
+	core.data[pc] = {
+		opcode: 'JMP',
+		a: { mode: 'direct', value: -3 },
+		b: { mode: 'direct', value: 0 },
+	};
+	const ins = core.data[pc];
+
+	expect(JMP(core, pc, ins)).toEqual([CORESIZE-1]);
+});