[Bug rtl-optimization/55393] gcc/g++ multiplies two unsigned integers using the IMULQ instruction

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55393



Jakub Jelinek <jakub at gcc dot gnu.org> changed:



           What    |Removed                     |Added

----------------------------------------------------------------------------

             Status|UNCONFIRMED                 |RESOLVED

         Resolution|                            |INVALID



--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-11-20 
07:56:32 UTC ---

long long never stopped being 128-bit on x86_64 and other 64-bit architectures

GCC supports, it simply always used to be 64-bit.  If you want 128-bit type,

there is unsigned __int128 supported in newer versions of GCC, so you can do

something like:

   if (((unsigned __int128) num * mult) >> 64)

      std::cout << "overflow" << std::endl;