compiler-rt/lib/builtins/multi3.c

   1 //===-- multi3.c - Implement __multi3 -------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file implements __multi3 for the compiler_rt library.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "int_lib.h"
  14
  15 #ifdef CRT_HAS_128BIT
  16
  17 // Returns: a * b
  18
  19 static ti_int __mulddi3(du_int a, du_int b) {
  20   twords r;
  21   const int bits_in_dword_2 = (int)(sizeof(di_int) * CHAR_BIT) / 2;
  22   const du_int lower_mask = (du_int)~0 >> bits_in_dword_2;
  23   r.s.low = (a & lower_mask) * (b & lower_mask);
  24   du_int t = r.s.low >> bits_in_dword_2;
  25   r.s.low &= lower_mask;
  26   t += (a >> bits_in_dword_2) * (b & lower_mask);
  27   r.s.low += (t & lower_mask) << bits_in_dword_2;
  28   r.s.high = t >> bits_in_dword_2;
  29   t = r.s.low >> bits_in_dword_2;
  30   r.s.low &= lower_mask;
  31   t += (b >> bits_in_dword_2) * (a & lower_mask);
  32   r.s.low += (t & lower_mask) << bits_in_dword_2;
  33   r.s.high += t >> bits_in_dword_2;
  34   r.s.high += (a >> bits_in_dword_2) * (b >> bits_in_dword_2);
  35   return r.all;
  36 }
  37
  38 // Returns: a * b
  39
  40 COMPILER_RT_ABI ti_int __multi3(ti_int a, ti_int b) {
  41   twords x;
  42   x.all = a;
  43   twords y;
  44   y.all = b;
  45   twords r;
  46   r.all = __mulddi3(x.s.low, y.s.low);
  47   r.s.high += x.s.high * y.s.low + x.s.low * y.s.high;
  48   return r.all;
  49 }
  50
  51 #endif // CRT_HAS_128BIT