lib/muloti4.c

   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