/*
 * 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 pow.c
 * @brief Implements the OP_POW opcode for exponentiation in the VM.
 *
 * This file handles the OP_POW instruction, which computes the power of two integer values.
 * The values are popped from the stack, and the result is pushed back.
 *
 * Behavior:
 * - Pops two integer values from the stack.
 * - Computes the power of the first value raised to the second.
 * - Pushes the result onto the stack.
 *
 * Error Handling:
 * - Exits with an error if the operands are not integers.
 *
 * Example:
 * - Bytecode: OP_POW
 * - Stack before: [2, 3]
 * - Stack after: [8]
 */

case OP_POW: {
  Value b = pop_value(vm);
  Value a = pop_value(vm);
  if (a.type != VAL_INT || b.type != VAL_INT) {
    fprintf(stderr, "POW expects ints\n");
    exit(1);
  }
  int64_t base = a.i;
  int64_t exp = b.i;
  int64_t res = 1;
  if (exp < 0) {
    res = 0;
  } else {
    while (exp > 0) {
      if (exp & 1) res *= base;
      base *= base;
      exp >>= 1;
    }
  }
  push_value(vm, make_int(res));
  free_value(a);
  free_value(b);
  break;
}
