1 /*===-- muloti4.c - Implement __muloti4 -----------------------------------=== 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 __muloti4 for the compiler_rt library. 11 * 12 * ===----------------------------------------------------------------------=== 13 */ 14 15 #include "int_lib.h" 16 17 #if __x86_64 18 19 /* Returns: a * b */ 20 21 /* Effects: sets *overflow to 1 if a * b overflows */ 22 23 ti_int 24 __muloti4(ti_int a, ti_int b, int* overflow) 25 { 26 const int N = (int)(sizeof(ti_int) * CHAR_BIT); 27 const ti_int MIN = (ti_int)1 << (N-1); 28 const ti_int MAX = ~MIN; 29 *overflow = 0; 30 ti_int result = a * b; 31 if (a == MIN) 32 { 33 if (b != 0 && b != 1) 34 *overflow = 1; 35 return result; 36 } 37 if (b == MIN) 38 { 39 if (a != 0 && a != 1) 40 *overflow = 1; 41 return result; 42 } 43 ti_int sa = a >> (N - 1); 44 ti_int abs_a = (a ^ sa) - sa; 45 ti_int sb = b >> (N - 1); 46 ti_int abs_b = (b ^ sb) - sb; 47 if (abs_a < 2 || abs_b < 2) 48 return result; 49 if (sa == sb) 50 { 51 if (abs_a > MAX / abs_b) 52 *overflow = 1; 53 } 54 else 55 { 56 if (abs_a > MIN / -abs_b) 57 *overflow = 1; 58 } 59 return result; 60 } 61 62 #endif 63
