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      1 /*===-- mulodi4.c - Implement __mulodi4 -----------------------------------===
      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 __mulodi4 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 di_int
     22 __mulodi4(di_int a, di_int b, int* overflow)
     23 {
     24     const int N = (int)(sizeof(di_int) * CHAR_BIT);
     25     const di_int MIN = (di_int)1 << (N-1);
     26     const di_int MAX = ~MIN;
     27     *overflow = 0;
     28     di_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     di_int sa = a >> (N - 1);
     42     di_int abs_a = (a ^ sa) - sa;
     43     di_int sb = b >> (N - 1);
     44     di_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