On Wed, Aug 12, 2015 at 10:52 PM, Mike Stump <mikest...@comcast.net> wrote: > On Aug 12, 2015, at 1:07 PM, Richard Sandiford <rdsandif...@googlemail.com> > wrote: >>> I don't think the right shifts are an issue at all. >> >> Well, they're implementation-defined, at least in C. > >> The C11 wording for E1 >> E2 is "If E1 has a signed type and a negative >> value, the >> resulting value is implementation-defined”. > >> Is C++ different? > > No, it is the same: > > 3 The value of E1 >> E2 is E1 right-shifted E2 bit positions. If E1 has > an unsigned type or if E1 has a signed type and a nonnegative value, > the value of the result is the integral part of the quotient of E1 > divided by the quantity 2 raised to the power E2. If E1 has a signed > type and a negative value, the resulting value is implementation- > defined.
Ok, then guard the << >> with __GCC__ and do the expensive bit stuff otherwise. Just to cater for other host compilers doing sth unsensibly implementation defined. This thing _is_ performance critical. Richard. >> (I don't have the standard handy.) > > Google is your friend.
