1/*===-- int128_builtins.cpp - Implement __muloti4 --------------------------===
2 *
3 * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 * See https://llvm.org/LICENSE.txt for license information.
5 * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 *
7 * ===----------------------------------------------------------------------===
8 *
9 * This file implements __muloti4, and is stolen from the compiler_rt library.
10 *
11 * FIXME: we steal and re-compile it into filesystem, which uses __int128_t,
12 * and requires this builtin when sanitized. See llvm.org/PR30643
13 *
14 * ===----------------------------------------------------------------------===
15 */
16#include <__config>
17#include <climits>
18
19#if !defined(_LIBCPP_HAS_NO_INT128)
20
21extern "C" __attribute__((no_sanitize("undefined"))) _LIBCPP_FUNC_VIS
22__int128_t __muloti4(__int128_t a, __int128_t b, int* overflow) {
23  const int N = (int)(sizeof(__int128_t) * CHAR_BIT);
24  const __int128_t MIN = (__int128_t)1 << (N - 1);
25  const __int128_t MAX = ~MIN;
26  *overflow = 0;
27  __int128_t result = a * b;
28  if (a == MIN) {
29    if (b != 0 && b != 1)
30      *overflow = 1;
31    return result;
32  }
33  if (b == MIN) {
34    if (a != 0 && a != 1)
35      *overflow = 1;
36    return result;
37  }
38  __int128_t sa = a >> (N - 1);
39  __int128_t abs_a = (a ^ sa) - sa;
40  __int128_t sb = b >> (N - 1);
41  __int128_t abs_b = (b ^ sb) - sb;
42  if (abs_a < 2 || abs_b < 2)
43    return result;
44  if (sa == sb) {
45    if (abs_a > MAX / abs_b)
46      *overflow = 1;
47  } else {
48    if (abs_a > MIN / -abs_b)
49      *overflow = 1;
50  }
51  return result;
52}
53
54#endif
55