[PATCH] Improve _Safe_iterator _M_distance_to

[François Dumont]

I eventually committed the attach patch.

The usage of __dp_sign_max_size will come later.

François

On 9/27/19 1:45 PM, Jonathan Wakely wrote:
> 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.
>
>
>

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