1219820Sjeff/*===-- int128_builtins.cpp - Implement __muloti4 --------------------------===
2219820Sjeff *
3219820Sjeff * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4219820Sjeff * See https://llvm.org/LICENSE.txt for license information.
5219820Sjeff * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6219820Sjeff *
7219820Sjeff * ===----------------------------------------------------------------------===
8219820Sjeff *
9219820Sjeff * This file implements __muloti4, and is stolen from the compiler_rt library.
10219820Sjeff *
11219820Sjeff * FIXME: we steal and re-compile it into filesystem, which uses __int128_t,
12219820Sjeff * and requires this builtin when sanitized. See llvm.org/PR30643
13219820Sjeff *
14219820Sjeff * ===----------------------------------------------------------------------===
15219820Sjeff */
16219820Sjeff#include <__config>
17219820Sjeff#include <climits>
18219820Sjeff
19219820Sjeff#if !defined(_LIBCPP_HAS_NO_INT128)
20219820Sjeff
21219820Sjeffextern "C" __attribute__((no_sanitize("undefined"))) _LIBCPP_FUNC_VIS
22219820Sjeff__int128_t __muloti4(__int128_t a, __int128_t b, int* overflow) {
23219820Sjeff  const int N = (int)(sizeof(__int128_t) * CHAR_BIT);
24219820Sjeff  const __int128_t MIN = (__int128_t)1 << (N - 1);
25219820Sjeff  const __int128_t MAX = ~MIN;
26219820Sjeff  *overflow = 0;
27219820Sjeff  __int128_t result = a * b;
28219820Sjeff  if (a == MIN) {
29219820Sjeff    if (b != 0 && b != 1)
30219820Sjeff      *overflow = 1;
31219820Sjeff    return result;
32219820Sjeff  }
33219820Sjeff  if (b == MIN) {
34219820Sjeff    if (a != 0 && a != 1)
35219820Sjeff      *overflow = 1;
36219820Sjeff    return result;
37219820Sjeff  }
38219820Sjeff  __int128_t sa = a >> (N - 1);
39219820Sjeff  __int128_t abs_a = (a ^ sa) - sa;
40219820Sjeff  __int128_t sb = b >> (N - 1);
41219820Sjeff  __int128_t abs_b = (b ^ sb) - sb;
42219820Sjeff  if (abs_a < 2 || abs_b < 2)
43219820Sjeff    return result;
44219820Sjeff  if (sa == sb) {
45219820Sjeff    if (abs_a > MAX / abs_b)
46219820Sjeff      *overflow = 1;
47219820Sjeff  } else {
48219820Sjeff    if (abs_a > MIN / -abs_b)
49219820Sjeff      *overflow = 1;
50219820Sjeff  }
51219820Sjeff  return result;
52219820Sjeff}
53219820Sjeff
54219820Sjeff#endif
55219820Sjeff