1 /*===-- mulosi4.c - Implement __mulosi4 -----------------------------------=== 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 __mulosi4 for the compiler_rt library. 11 * 12 * ===----------------------------------------------------------------------=== 13 */ 14 15 #include "int_lib.h" 16 17 /* Returns: a * b */ 18 19 /* Effects: sets *overflow to 1 if a * b overflows */ 20 21 COMPILER_RT_ABI si_int 22 __mulosi4(si_int a, si_int b, int* overflow) 23 { 24 const int N = (int)(sizeof(si_int) * CHAR_BIT); 25 const si_int MIN = (si_int)1 << (N-1); 26 const si_int MAX = ~MIN; 27 *overflow = 0; 28 si_int result = a * b; 29 if (a == MIN) 30 { 31 if (b != 0 && b != 1) 32 *overflow = 1; 33 return result; 34 } 35 if (b == MIN) 36 { 37 if (a != 0 && a != 1) 38 *overflow = 1; 39 return result; 40 } 41 si_int sa = a >> (N - 1); 42 si_int abs_a = (a ^ sa) - sa; 43 si_int sb = b >> (N - 1); 44 si_int abs_b = (b ^ sb) - sb; 45 if (abs_a < 2 || abs_b < 2) 46 return result; 47 if (sa == sb) 48 { 49 if (abs_a > MAX / abs_b) 50 *overflow = 1; 51 } 52 else 53 { 54 if (abs_a > MIN / -abs_b) 55 *overflow = 1; 56 } 57 return result; 58 } 59
