lib/builtins/mulvti3.c

   1 /* ===-- mulvti3.c - Implement __mulvti3 -----------------------------------===
   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 __mulvti3 for the compiler_rt library.
  11  *
  12  * ===----------------------------------------------------------------------===
  13  */
  14
  15 #include "int_lib.h"
  16
  17 #ifdef CRT_HAS_128BIT
  18
  19 /* Returns: a * b */
  20
  21 /* Effects: aborts if a * b overflows */
  22
  23 COMPILER_RT_ABI ti_int
  24 __mulvti3(ti_int a, ti_int b)
  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     if (a == MIN)
  30     {
  31         if (b == 0 || b == 1)
  32             return a * b;
  33         compilerrt_abort();
  34     }
  35     if (b == MIN)
  36     {
  37         if (a == 0 || a == 1)
  38             return a * b;
  39         compilerrt_abort();
  40     }
  41     ti_int sa = a >> (N - 1);
  42     ti_int abs_a = (a ^ sa) - sa;
  43     ti_int sb = b >> (N - 1);
  44     ti_int abs_b = (b ^ sb) - sb;
  45     if (abs_a < 2 || abs_b < 2)
  46         return a * b;
  47     if (sa == sb)
  48     {
  49         if (abs_a > MAX / abs_b)
  50             compilerrt_abort();
  51     }
  52     else
  53     {
  54         if (abs_a > MIN / -abs_b)
  55             compilerrt_abort();
  56     }
  57     return a * b;
  58 }
  59
  60 #endif /* CRT_HAS_128BIT */