status changed; resolution set

Ion Gaztañaga — Fri, 19 Aug 2016 18:50:26 GMT

status new → closed
resolution → invalid

That function is only called if sizeof(std::size_t)*CHAR_BIT is 64:

   inline std::size_t floor_log2 (std::size_t x)
   {
      const std::size_t Bits = sizeof(std::size_t)*CHAR_BIT;
      return floor_log2(x, integral_constant<std::size_t, Bits>());
   }

The 32 bit version uses only 16 bit shift:

   inline std::size_t floor_log2 (std::size_t v, integral_constant<std::size_t, 32>)
   {
      static const int MultiplyDeBruijnBitPosition[32] =
      {
         0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30,
         8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31
      };
      v |= v >> 1;
      v |= v >> 2;
      v |= v >> 4;
      v |= v >> 8;
      v |= v >> 16;
      return MultiplyDeBruijnBitPosition[(std::size_t)(v * 0x07C4ACDDU) >> 27];
   }

Boost C++ Libraries: Ticket #12401: UB when sizeof(std::size_t) in floor_log2

status changed; resolution set