/**
 * This file is part of the Fun programming language.
 * https://fun-lang.xyz/
 *
 * Copyright 2025 Johannes Findeisen <you@hanez.org>
 * Licensed under the terms of the Apache-2.0 license.
 * https://opensource.org/license/apache-2-0
 */

/**
 * @file swap.c
 * @brief Implements the OP_SWAP opcode for stack manipulation in the VM.
 *
 * This file handles the OP_SWAP instruction, which swaps the top two values
 * on the stack.
 *
 * Behavior:
 * - Swaps stack[sp] and stack[sp-1]
 * - No type checking
 *
 * Error Handling:
 * - Exits if stack underflow
 *
 * @author Johannes Findeisen
 * @date 2025-10-16
 */

case OP_SWAP: {
  if (vm->sp < 1) {
    fprintf(stderr, "Runtime error: stack underflow for SWAP\n");
    exit(1);
  }
  Value a = vm->stack[vm->sp];
  Value b = vm->stack[vm->sp - 1];
  vm->stack[vm->sp] = b;
  vm->stack[vm->sp - 1] = a;
  break;
}