Revert "[OpJumpFalse, OpAndJump, OpOrJump, OpJump], these four instru…

…ctions have been changed to use 4 bytes to avoid precision loss and panic when the number of instructions exceeds the maximum of 16 bits (65535) (#433)" (#436)

This reverts commit 18424de.

instructions.go

@@ -28,12 +28,6 @@ func MakeInstruction(opcode parser.Opcode, operands ...int) []byte {
 			n := uint16(o)
 			instruction[offset] = byte(n >> 8)
 			instruction[offset+1] = byte(n)
-		case 4:
-			n := uint32(o)
-			instruction[offset] = byte(n >> 24)
-			instruction[offset+1] = byte(n >> 16)
-			instruction[offset+2] = byte(n >> 8)
-			instruction[offset+3] = byte(n)
 		}
 		offset += width
 	}

parser/opcodes.go

@@ -106,10 +106,10 @@ var OpcodeOperands = [...][]int{
 	OpNotEqual:      {},
 	OpMinus:         {},
 	OpLNot:          {},
-	OpJumpFalsy:     {4},
-	OpAndJump:       {4},
-	OpOrJump:        {4},
-	OpJump:          {4},
+	OpJumpFalsy:     {2},
+	OpAndJump:       {2},
+	OpOrJump:        {2},
+	OpJump:          {2},
 	OpNull:          {},
 	OpGetGlobal:     {2},
 	OpSetGlobal:     {2},
@@ -149,8 +149,6 @@ func ReadOperands(numOperands []int, ins []byte) (operands []int, offset int) {
 			operands = append(operands, int(ins[offset]))
 		case 2:
 			operands = append(operands, int(ins[offset+1])|int(ins[offset])<<8)
-		case 4:
-			operands = append(operands, int(ins[offset+3])|int(ins[offset+2])<<8|int(ins[offset+1])<<16|int(ins[offset])<<24)
 		}
 		offset += width
 	}

vm.go

@@ -218,30 +218,30 @@ func (v *VM) run() {
 				return
 			}
 		case parser.OpJumpFalsy:
-			v.ip += 4
+			v.ip += 2
 			v.sp--
 			if v.stack[v.sp].IsFalsy() {
-				pos := int(v.curInsts[v.ip]) | int(v.curInsts[v.ip-1])<<8 | int(v.curInsts[v.ip-2])<<16 | int(v.curInsts[v.ip-3])<<24
+				pos := int(v.curInsts[v.ip]) | int(v.curInsts[v.ip-1])<<8
 				v.ip = pos - 1
 			}
 		case parser.OpAndJump:
-			v.ip += 4
+			v.ip += 2
 			if v.stack[v.sp-1].IsFalsy() {
-				pos := int(v.curInsts[v.ip]) | int(v.curInsts[v.ip-1])<<8 | int(v.curInsts[v.ip-2])<<16 | int(v.curInsts[v.ip-3])<<24
+				pos := int(v.curInsts[v.ip]) | int(v.curInsts[v.ip-1])<<8
 				v.ip = pos - 1
 			} else {
 				v.sp--
 			}
 		case parser.OpOrJump:
-			v.ip += 4
+			v.ip += 2
 			if v.stack[v.sp-1].IsFalsy() {
 				v.sp--
 			} else {
-				pos := int(v.curInsts[v.ip]) | int(v.curInsts[v.ip-1])<<8 | int(v.curInsts[v.ip-2])<<16 | int(v.curInsts[v.ip-3])<<24
+				pos := int(v.curInsts[v.ip]) | int(v.curInsts[v.ip-1])<<8
 				v.ip = pos - 1
 			}
 		case parser.OpJump:
-			pos := int(v.curInsts[v.ip+4]) | int(v.curInsts[v.ip+3])<<8 | int(v.curInsts[v.ip+2])<<16 | int(v.curInsts[v.ip+1])<<24
+			pos := int(v.curInsts[v.ip+2]) | int(v.curInsts[v.ip+1])<<8
 			v.ip = pos - 1
 		case parser.OpSetGlobal:
 			v.ip += 2