lib/multi3.c

   1 /* ===-- multi3.c - Implement __multi3 -------------------------------------===
   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 __multi3 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 static
  22 ti_int
  23 __mulddi3(du_int a, du_int b)
  24 {
  25     twords r;
  26     const int bits_in_dword_2 = (int)(sizeof(di_int) * CHAR_BIT) / 2;
  27     const du_int lower_mask = (du_int)~0 >> bits_in_dword_2;
  28     r.s.low = (a & lower_mask) * (b & lower_mask);
  29     du_int t = r.s.low >> bits_in_dword_2;
  30     r.s.low &= lower_mask;
  31     t += (a >> bits_in_dword_2) * (b & lower_mask);
  32     r.s.low += (t & lower_mask) << bits_in_dword_2;
  33     r.s.high = t >> bits_in_dword_2;
  34     t = r.s.low >> bits_in_dword_2;
  35     r.s.low &= lower_mask;
  36     t += (b >> bits_in_dword_2) * (a & lower_mask);
  37     r.s.low += (t & lower_mask) << bits_in_dword_2;
  38     r.s.high += t >> bits_in_dword_2;
  39     r.s.high += (a >> bits_in_dword_2) * (b >> bits_in_dword_2);
  40     return r.all;
  41 }
  42
  43 /* Returns: a * b */
  44
  45 ti_int
  46 __multi3(ti_int a, ti_int b)
  47 {
  48     twords x;
  49     x.all = a;
  50     twords y;
  51     y.all = b;
  52     twords r;
  53     r.all = __mulddi3(x.s.low, y.s.low);
  54     r.s.high += x.s.high * y.s.low + x.s.low * y.s.high;
  55     return r.all;
  56 }
  57
  58 #endif /* __x86_64 */