------- Comment #8 from potswa at mac dot com 2009-09-14 21:36 -------
Well, if fast is good, maybe you will consider this:
const _Distance __d = __gcd(__n, __k), __r = __n / __d;
for ( _Distance __i = 0; __i < __d; ++ __i ) {
_ValueType __tmp = *__first;
_RandomAccessIterator __p = __first + __l;
for ( _Distance __j = 0; ; ) {
swap( __tmp, * __p );
if ( ++ __j >= __r ) break;
if ( __p >= __middle ) __p -= __n - __l;
else __p += __l;
}
++ __first;
}
It's a few times faster than the current implementation for the case of many
small rings, and seems to be within 1% otherwise for both large and small data
structures. (The way __tmp is used, it can always be optimized out.) There is a
small penalty which seems to go away if I manually unroll the inner loop, which
is annoying.
It's also much, much more elegant.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41351
