[libcxx-commits] [libcxx] [libc++] Optimize rotate (PR #120890)

[Louis Dionne via libcxx-commits]

================
@@ -89,46 +86,31 @@ __rotate_forward(_ForwardIterator __first, _ForwardIterator __middle, _ForwardIt
   return __r;
 }
 
-template <typename _Integral>
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 _Integral __algo_gcd(_Integral __x, _Integral __y) {
-  do {
-    _Integral __t = __x % __y;
-    __x           = __y;
-    __y           = __t;
-  } while (__y);
-  return __x;
-}
-
-template <class _AlgPolicy, typename _RandomAccessIterator>
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 _RandomAccessIterator
-__rotate_gcd(_RandomAccessIterator __first, _RandomAccessIterator __middle, _RandomAccessIterator __last) {
-  typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type;
-  typedef typename iterator_traits<_RandomAccessIterator>::value_type value_type;
-  using _Ops = _IterOps<_AlgPolicy>;
-
-  const difference_type __m1 = __middle - __first;
-  const difference_type __m2 = _Ops::distance(__middle, __last);
-  if (__m1 == __m2) {
-    std::__swap_ranges<_AlgPolicy>(__first, __middle, __middle, __last);
-    return __middle;
-  }
-  const difference_type __g = std::__algo_gcd(__m1, __m2);
-  for (_RandomAccessIterator __p = __first + __g; __p != __first;) {
-    value_type __t(_Ops::__iter_move(--__p));
-    _RandomAccessIterator __p1 = __p;
-    _RandomAccessIterator __p2 = __p1 + __m1;
-    do {
-      *__p1                     = _Ops::__iter_move(__p2);
-      __p1                      = __p2;
-      const difference_type __d = _Ops::distance(__p2, __last);
-      if (__m1 < __d)
-        __p2 += __m1;
-      else
-        __p2 = __first + (__m1 - __d);
-    } while (__p2 != __p);
-    *__p1 = std::move(__t);
+template <class _AlgPolicy, class _Iter, class _Sent>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 _Iter __rotate_random(_Iter __first, _Iter __middle, _Sent __sent) {
----------------
ldionne wrote:

```suggestion
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 _Iter __rotate_random_access(_Iter __first, _Iter __middle, _Sent __sent) {
```

https://github.com/llvm/llvm-project/pull/120890