Currently, the multisig descriptor constructions are limited to 16 keys only possibly because of template parsing reasons. Under p2sh context, such scripts would be invalid anyway because of 520-byte rule, but we can support up to 20 keys for CHECKMULTISIG in witness script context. 


stack.push_back(vch1);
                    stack.push_back(vch2);
                }
                break;
                case OP_3DUP:
                {
                    
                    if (stack.size() < 3)
                        return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                    valtype vch1 = stacktop(-3);
                    valtype vch2 = stacktop(-2);
                    valtype vch3 = stacktop(-1);
                    stack.push_back(vch1);
                    stack.push_back(vch2);
                    stack.push_back(vch3);
                }
                break;
                case OP_2OVER:
                {
                    
                    if (stack.size() < 4)
                        return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                    valtype vch1 = stacktop(-4);
                    valtype vch2 = stacktop(-3);
                    stack.push_back(vch1);
                    stack.push_back(vch2);
                }
                break;
                case OP_2ROT:
                {