1 //===-- muloti4.c - 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 for the compiler_rt library. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #include "int_lib.h" 14 15 #ifdef CRT_HAS_128BIT 16 17 // Returns: a * b 18 19 // Effects: sets *overflow to 1 if a * b overflows 20 21 COMPILER_RT_ABI ti_int __muloti4(ti_int a, ti_int b, int *overflow) { 22 const int N = (int)(sizeof(ti_int) * CHAR_BIT); 23 const ti_int MIN = (ti_int)1 << (N - 1); 24 const ti_int MAX = ~MIN; 25 *overflow = 0; 26 ti_int result = a * b; 27 if (a == MIN) { 28 if (b != 0 && b != 1) 29 *overflow = 1; 30 return result; 31 } 32 if (b == MIN) { 33 if (a != 0 && a != 1) 34 *overflow = 1; 35 return result; 36 } 37 ti_int sa = a >> (N - 1); 38 ti_int abs_a = (a ^ sa) - sa; 39 ti_int sb = b >> (N - 1); 40 ti_int abs_b = (b ^ sb) - sb; 41 if (abs_a < 2 || abs_b < 2) 42 return result; 43 if (sa == sb) { 44 if (abs_a > MAX / abs_b) 45 *overflow = 1; 46 } else { 47 if (abs_a > MIN / -abs_b) 48 *overflow = 1; 49 } 50 return result; 51 } 52 53 #endif // CRT_HAS_128BIT 54