55 lines · 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-exception6 *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/PR3064313 *14 * ===----------------------------------------------------------------------===15 */16#include <__config>17#include <climits>18 19#if _LIBCPP_HAS_INT12820 21extern "C" __attribute__((no_sanitize("undefined"))) _LIBCPP_EXPORTED_FROM_ABI __int128_t22__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#endif55