[PATCH] Improve _Safe_iterator _M_distance_to

[Jonathan Wakely]

On 16/09/19 22:31 +0200, François Dumont wrote:
>Â Â Â  Here is the patch to improve _Safe_iterator<>::_M_get_distance_to 
>implementation.
>
>I introduced a new _Distance_precision  __sp_sign_max_size for 
>occasions where we can't find out the exact size of a range but still 
>get the max size of it. Thanks to this the performance tests are much 
>better when dealing with list iterators:
>
>Normal mode:
>
>copy_backward_deque_iterators.cc    deque 2 list 5616r 5616u    
>0s         0mem    0pf
>copy_backward_deque_iterators.cc    list 2 deque 1586r 1586u    
>0s         0mem    0pf
>copy_deque_iterators.cc      deque 2 list                 5495r 
>5495u    0s         0mem    0pf
>copy_deque_iterators.cc      list 2 deque                 2400r 
>2400u    0s         0mem    0pf
>
>Debug mode:
>
>copy_backward_deque_iterators.cc    deque 2 list 5789r 5785u    
>1s         0mem    0pf
>copy_backward_deque_iterators.cc    list 2 deque 1656r 1655u    
>0s         0mem    0pf
>copy_deque_iterators.cc      deque 2 list                 5792r 
>5793u    0s         0mem    0pf
>copy_deque_iterators.cc      list 2 deque                 2636r 
>2636u    0s         0mem    0pf
>
>Tested under Linux x86_64.
>
>I'll commit once other patches are in.
>
>
>Â Â Â  * include/debug/forward_list
>(_Sequence_traits<__debug::forward_list<>>::_S_size): Returns __dp_sign
>Â Â Â  distance when not empty.
>Â Â Â  * include/debug/list
>Â Â Â  (_Sequence_traits<__debug::list<>>::_S_size): Likewise.
>Â Â Â  * include/debug/helper_functions.h (__dp_sign_max_size): New
>Â Â Â  _Distance_precision enum entry.
>Â Â Â  * include/debug/safe_iterator.h
>Â Â Â  (__copy_move_a(_II, _II, const _Safe_iterator<>&)): Check for output
>Â Â Â  iterator _M_can_advance as soon as input range distance precision is
>Â Â Â  strictly higher than __dp_size.
>Â Â Â  (__copy_move_a(const _Safe_iterator<>&, const _Safe_iterator<>&,
>Â Â Â  const _Safe_iterator<>&)): Likewise.
>Â Â Â  (__copy_move_backward_a(_II, _II, const _Safe_iterator<>&)): Likewise.
>Â Â Â  (__copy_move_backward_a(const _Safe_iterator<>&,
>Â Â Â  const _Safe_iterator<>&, const _Safe_iterator<>&)): Likewise.
>Â Â Â  (__equal_aux(_II, _II, const _Safe_iterator<>&)): Likewise.
>Â Â Â  (__equal_aux(const _Safe_iterator<>&,
>Â Â Â  const _Safe_iterator<>&, const _Safe_iterator<>&)): Likewise.

The patch looks OK, but the safe_iterator.tcc changes are not listed
in the changelog, and those are the most complex part of the patch.

Please add a changelog entry for the _M_get_distance_to changes. OK
for trunk after that, thanks.