[PATCH][Hashtable 1/6] Code simplification/optimization

[Jonathan Wakely]

On 17/11/19 21:51 +0100, François Dumont wrote:
>This patch simplifies a number of implementations.
>
>It tries as much as possible to avoid computing hash code. This is 
>especially true for the erase implementation in case of multi keys.
>
>
>Â Â Â  * include/bits/hashtable_policy.h (_Map_base<>::at): Use
>Â Â Â  _Hashtable<>::find.
>(_Hashtable_base<>::_Equal_hash_code<>::_S_node_equals):New.
>Â Â Â  (_Hashtable_base<>::_M_node_equals): New, use latter.
>Â Â Â  * include/bits/hashtable.h (_Hashtable<>::_M_update_bbegin): New.
>Â Â Â  (_Hashtable<>::_M_assign): Use latter.
>Â Â Â  (_Hashtable<>::_M_move_assign): Likewise.
>Â Â Â  (_Hashtable<>(_Hashtable<>&&)): Likewise.
>Â Â Â  (_Hashtable<>(_Hashtable<>&&, const allocator_type&)): Likewise.
>Â Â Â  (_Hashtable<>::swap): Likewise.
>Â Â Â  (_Hashtable<>::find): Build iterator directly from _M_find_node result.
>Â Â Â  (_Hashtable<>::count): Use _Hashtable<>::find.
>Â Â Â  (_Hashtable<>::equal_range): Likewise.
>Â Â Â  (_Hashtable<>::_M_erase(false_type, const key_type&)): Use
>Â Â Â  _M_node_equals.
>
>Tested under Linux x86_64.

OK for master except for one comment ...


>@@ -1457,14 +1466,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>       std::swap(_M_element_count, __x._M_element_count);
>       std::swap(_M_single_bucket, __x._M_single_bucket);
> 
>-      // Fix buckets containing the _M_before_begin pointers that can't be
>-      // swapped.
>-      if (_M_begin())
>-	_M_buckets[_M_bucket_index(_M_begin())] = &_M_before_begin;
>-
>-      if (__x._M_begin())
>-	__x._M_buckets[__x._M_bucket_index(__x._M_begin())]
>-	  = &__x._M_before_begin;
>+      // Fix bucket containing the _M_before_begin pointer that can't be swap.

"can't be swap" should be "can't be swapped" as it was in the original
comment.

OK with that change, thanks.


>+      _M_update_bbegin();
>+      __x._M_update_bbegin();
>     }
> 
>   template<typename _Key, typename _Value,