[PATCH] Improve _Safe_iterator _M_distance_to

Mon Sep 16 20:31:00 GMT 2019

 Â Â Â  Here is the patch to improve _Safe_iterator<>::_M_get_distance_to 
implementation.

I introduced a new _Distance_precisionÂ  __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.ccÂ Â Â  deque 2 list 5616r 5616uÂ Â Â  
0sÂ Â Â Â Â Â Â Â  0memÂ Â Â  0pf
copy_backward_deque_iterators.ccÂ Â Â  list 2 deque 1586r 1586uÂ Â Â  
0sÂ Â Â Â Â Â Â Â  0memÂ Â Â  0pf
copy_deque_iterators.ccÂ  Â Â Â  deque 2 listÂ Â Â Â Â Â Â Â Â Â Â Â  Â Â Â  5495r 5495uÂ Â Â  
0sÂ Â Â Â Â Â Â Â  0memÂ Â Â  0pf
copy_deque_iterators.ccÂ  Â Â Â  list 2 dequeÂ Â Â Â Â Â Â Â Â Â Â Â  Â Â Â  2400r 2400uÂ Â Â  
0sÂ Â Â Â Â Â Â Â  0memÂ Â Â  0pf

Debug mode:

copy_backward_deque_iterators.ccÂ Â Â  deque 2 list 5789r 5785uÂ Â Â  
1sÂ Â Â Â Â Â Â Â  0memÂ Â Â  0pf
copy_backward_deque_iterators.ccÂ Â Â  list 2 deque 1656r 1655uÂ Â Â  
0sÂ Â Â Â Â Â Â Â  0memÂ Â Â  0pf
copy_deque_iterators.ccÂ  Â Â Â  deque 2 listÂ Â Â Â Â Â Â Â Â Â Â Â  Â Â Â  5792r 5793uÂ Â Â  
0sÂ Â Â Â Â Â Â Â  0memÂ Â Â  0pf
copy_deque_iterators.ccÂ  Â Â Â  list 2 dequeÂ Â Â Â Â Â Â Â Â Â Â Â  Â Â Â  2636r 2636uÂ Â Â  
0sÂ Â Â Â Â Â Â Â  0memÂ Â Â  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.

FranÃ§ois

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