/*===-- int128_builtins.cpp - Implement __muloti4 --------------------------===

 *

 * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

 * See https://llvm.org/LICENSE.txt for license information.

 * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

 *

 * ===----------------------------------------------------------------------===

 *

 * This file implements __muloti4, and is stolen from the compiler_rt library.

 *

 * FIXME: we steal and re-compile it into filesystem, which uses __int128_t,

 * and requires this builtin when sanitized. See llvm.org/PR30643

 *

 * ===----------------------------------------------------------------------===

 */

#include <__config>

#include <climits>

#if !defined(_LIBCPP_HAS_NO_INT128)

extern "C" __attribute__((no_sanitize("undefined"))) _LIBCPP_FUNC_VIS

__int128_t __muloti4(__int128_t a, __int128_t b, int* overflow) {

  const int N = (int)(sizeof(__int128_t) * CHAR_BIT);

  const __int128_t MIN = (__int128_t)1 << (N - 1);

  const __int128_t MAX = ~MIN;

  *overflow = 0;

  __int128_t result = a * b;

  if (a == MIN) {

    if (b != 0 && b != 1)

      *overflow = 1;

    return result;

  }

  if (b == MIN) {

    if (a != 0 && a != 1)

      *overflow = 1;

    return result;

  }

  __int128_t sa = a >> (N - 1);

  __int128_t abs_a = (a ^ sa) - sa;

  __int128_t sb = b >> (N - 1);

  __int128_t abs_b = (b ^ sb) - sb;

  if (abs_a < 2 || abs_b < 2)

    return result;

  if (sa == sb) {

    if (abs_a > MAX / abs_b)

      *overflow = 1;

  } else {

    if (abs_a > MIN / -abs_b)

      *overflow = 1;

  }

  return result;

}

#endif