OP_ROLL

src/script/engine.zig

@@ -153,6 +153,7 @@ pub const Engine = struct {
             Opcode.OP_CHECKSIG => try self.opCheckSig(),
             Opcode.OP_NIP => try self.opNip(),
             Opcode.OP_OVER => try self.opOver(),
+            Opcode.OP_ROLL => try self.opRoll(),
             Opcode.OP_PICK => try self.opPick(),
             Opcode.OP_SWAP => try self.opSwap(),
             Opcode.OP_TUCK => try self.opTuck(),
@@ -351,6 +352,23 @@ pub const Engine = struct {
         try self.stack.pushByteArray(value);
     }
 
+    /// OP_ROLL: Pop the top stack element as N. Move the Nth stack element to the top.
+    fn opRoll(self: *Engine) !void {
+        const n = try self.stack.popInt();
+
+        const index : usize = @intCast(n);
+        if (index >= self.stack.items.items.len) {
+            return error.StackUnderflow; 
+        }
+
+        const actualIndex = self.stack.items.items.len - 1 - index;
+
+        // Use orderedRemove to get the item
+        const value = self.stack.items.orderedRemove(actualIndex);
+
+        try self.stack.pushElement(value);
+    }
+
     /// OP_SWAP: The top two items on the stack are swapped.
     fn opSwap(self: *Engine) !void {
         const first = try self.stack.pop();
@@ -820,6 +838,28 @@ test "Script execution OP_1 OP_2 OP_3 OP_OVER" {
     try std.testing.expectEqual(3, element1);
 }
 
+test "Script execution OP_1 OP_2 OP_3 OP_2 OP_ROLL" {
+    const allocator = std.testing.allocator;
+
+    // Simple script: OP_1 OP_2 OP_3 OP_2 OP_ROLL
+    const script_bytes = [_]u8{ Opcode.OP_1.toBytes(), Opcode.OP_2.toBytes(), Opcode.OP_3.toBytes(), Opcode.OP_2.toBytes(), Opcode.OP_ROLL.toBytes() };
+    const script = Script.init(&script_bytes);
+
+    var engine = Engine.init(allocator, script, .{});
+    defer engine.deinit();
+
+    try engine.execute();
+    try std.testing.expectEqual(3, engine.stack.len());
+
+    const element0 = try engine.stack.peekInt(0);
+    const element1 = try engine.stack.peekInt(1);
+    const element2 = try engine.stack.peekInt(2);
+
+    try std.testing.expectEqual(1, element0);
+    try std.testing.expectEqual(3, element1);
+    try std.testing.expectEqual(2, element2);
+}
+
 test "Script execution OP_1 OP_2 OP_3 OP_SWAP" {
     const allocator = std.testing.allocator;