libcxx/src/filesystem/int128_builtins.cpp

   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 _LIBCPP_HAS_INT128
  20
  21 extern "C" __attribute__((no_sanitize("undefined"))) _LIBCPP_EXPORTED_FROM_ABI __int128_t
  22 __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