lib/builtins/mulvdi3.c

   1 /*===-- mulvdi3.c - Implement __mulvdi3 -----------------------------------===
   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 __mulvdi3 for the compiler_rt library.
  11  *
  12  * ===----------------------------------------------------------------------===
  13  */
  14
  15 #include "int_lib.h"
  16
  17 /* Returns: a * b */
  18
  19 /* Effects: aborts if a * b overflows */
  20
  21 COMPILER_RT_ABI di_int
  22 __mulvdi3(di_int a, di_int b)
  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     if (a == MIN)
  28     {
  29         if (b == 0 || b == 1)
  30             return a * b;
  31         compilerrt_abort();
  32     }
  33     if (b == MIN)
  34     {
  35         if (a == 0 || a == 1)
  36             return a * b;
  37         compilerrt_abort();
  38     }
  39     di_int sa = a >> (N - 1);
  40     di_int abs_a = (a ^ sa) - sa;
  41     di_int sb = b >> (N - 1);
  42     di_int abs_b = (b ^ sb) - sb;
  43     if (abs_a < 2 || abs_b < 2)
  44         return a * b;
  45     if (sa == sb)
  46     {
  47         if (abs_a > MAX / abs_b)
  48             compilerrt_abort();
  49     }
  50     else
  51     {
  52         if (abs_a > MIN / -abs_b)
  53             compilerrt_abort();
  54     }
  55     return a * b;
  56 }