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 21 extern "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