int128_builtins.cpp revision 336819 
1/*===-- int128_builtins.cpp - Implement __muloti4 --------------------------===
2 *
3 *                     The LLVM Compiler Infrastructure
4 *
5 * This file is dual licensed under the MIT and the University of Illinois Open
6 * Source Licenses. See LICENSE.TXT for details.
7 *
8 * ===----------------------------------------------------------------------===
9 *
10 * This file implements __muloti4, and is stolen from the compiler_rt library.
11 *
12 * FIXME: we steal and re-compile it into filesystem, which uses __int128_t,
13 * and requires this builtin when sanitized. See llvm.org/PR30643
14 *
15 * ===----------------------------------------------------------------------===
16 */
17#include "__config"
18#include "climits"
19
20#if !defined(_LIBCPP_HAS_NO_INT128)
21
22extern "C" __attribute__((no_sanitize("undefined")))
23__int128_t __muloti4(__int128_t a, __int128_t b, int* overflow) {
24  const int N = (int)(sizeof(__int128_t) * CHAR_BIT);
25  const __int128_t MIN = (__int128_t)1 << (N - 1);
26  const __int128_t MAX = ~MIN;
27  *overflow = 0;
28  __int128_t result = a * b;
29  if (a == MIN) {
30    if (b != 0 && b != 1)
31      *overflow = 1;
32    return result;
33  }
34  if (b == MIN) {
35    if (a != 0 && a != 1)
36      *overflow = 1;
37    return result;
38  }
39  __int128_t sa = a >> (N - 1);
40  __int128_t abs_a = (a ^ sa) - sa;
41  __int128_t sb = b >> (N - 1);
42  __int128_t abs_b = (b ^ sb) - sb;
43  if (abs_a < 2 || abs_b < 2)
44    return result;
45  if (sa == sb) {
46    if (abs_a > MAX / abs_b)
47      *overflow = 1;
48  } else {
49    if (abs_a > MIN / -abs_b)
50      *overflow = 1;
51  }
52  return result;
53}
54
55#endif
56