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 
22 extern "C" __attribute__((no_sanitize("undefined")))
__muloti4(__int128_t a,__int128_t b,int * overflow)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