From da09c300a5e2fa918e0c867031bc2a8e89071934 Mon Sep 17 00:00:00 2001
From: E Sequeira <5458743+geseq@users.noreply.github.com>
Date: Tue, 5 Dec 2023 20:52:53 +0000
Subject: [PATCH] Revert "[OpJumpFalse, OpAndJump, OpOrJump, OpJump], these
 four instructions 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 18424deb5a3a15277bc115fa173b9d27ac691583.
---
 instructions.go   |  6 ------
 parser/opcodes.go | 10 ++++------
 vm.go             | 14 +++++++-------
 3 files changed, 11 insertions(+), 19 deletions(-)

diff --git a/instructions.go b/instructions.go
index 27f7af3..eb1fbf2 100644
--- a/instructions.go
+++ b/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
 	}
diff --git a/parser/opcodes.go b/parser/opcodes.go
index c1e94c1..d97f489 100644
--- a/parser/opcodes.go
+++ b/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
 	}
diff --git a/vm.go b/vm.go
index 2f8f6fc..64bd23b 100644
--- a/vm.go
+++ b/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