Dynamic Bitsets in GCC

Правка en18, от bitset, 2024-05-13 23:50:33

Hello sirs, you might know that Boost has a dynamically sized bitset class, but did you know that GCC also has one? Turns out it's included in the tr2 folder. You can simply include the <tr2/dynamic_bitset> header, and use it as std::tr2::dynamic_bitset. Yes, it works on Codeforces.

Here's a code example to count triangles in a graph (abc258_g):

Code

In some problems, we might not be able to use a constant sized bitset. For example, on 1856E2 - PermuTree (hard version). Here's a submission where we replaced neal's custom_bitset template with using custom_bitset = tr2::dynamic_bitset<>;, and got accepted with little performance difference (260853192, original 217308610).

The implementation of the bitset seems identical to a version of Boost's dynamic bitset, so you can read the docs here. You can view the source here.

Comparing to std::bitset, here are some notable things I saw:

  • They include more set operations, such as set difference, and checking if a bitset is a subset of another bitset.
  • They include lexicographical comparisons between bitsets.
  • You can append single bits, as well as whole blocks (i.e. integers)
  • You can also resize it like a vector. (For some reason there's no pop_back though...)
  • Find first and find next are also supported, without weird function names like in std::bitset. Unfortunately, there's still no find previous :(
  • You can specify the word type and allocator as template arguments.

Of course, it also has all the normal std::bitset functionality. However, I'm not sure how fast this is compared to std::bitset; you can let me know in the comments. Interestingly, it seems to be using 64 bit integers on Codeforces.

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Thanks qmk for helping with the blog.

Теги bitset, gcc, boost

История

 
 
 
 
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  Rev. Язык Кто Когда Δ Комментарий
en22 Английский bitset 2024-06-12 19:17:27 150 Tiny change: 'gain when it's on Codef' -> 'gain when the fix is on Codef'
en21 Английский bitset 2024-06-08 23:19:49 50 (published)
en20 Английский bitset 2024-06-08 23:19:28 11
en19 Английский bitset 2024-06-08 23:12:35 272 Tiny change: '1157481). \n\nI'll keep ' -> '1157481). I'll keep ' (saved to drafts)
en18 Английский bitset 2024-05-13 23:50:33 0 (published)
en17 Английский bitset 2024-05-13 23:45:34 3 Tiny change: 'ames like std::bits' -> 'ames like in std::bits'
en16 Английский bitset 2024-05-13 23:42:07 1 Tiny change: 'difference and check' -> 'difference, and check'
en15 Английский bitset 2024-05-13 23:41:38 1 Tiny change: 'difference, and check' -> 'difference and check'
en14 Английский bitset 2024-05-13 23:39:11 7 Tiny change: 's all the std::bits' -> 's all the normal std::bits'
en13 Английский bitset 2024-05-13 23:37:23 17
en12 Английский bitset 2024-05-13 23:35:34 18
en11 Английский bitset 2024-05-13 23:31:33 14 Tiny change: 'mentation seems ide' -> 'mentation of the bitset seems ide'
en10 Английский bitset 2024-05-13 23:30:22 9 Tiny change: ' to use a max sized bit' -> ' to use a constant sized bit'
en9 Английский bitset 2024-05-13 23:29:46 21 Tiny change: 'er>\n\nIn problems with test cases, we migh' -> 'er>\n\nIn some problems, we migh'
en8 Английский bitset 2024-05-13 23:26:19 59 Tiny change: '] content.' -> '] content.\n\nThanks [user:qmk] for helping with the blog.'
en7 Английский bitset 2024-05-13 23:19:28 395 Tiny change: '260853192]).\n\n\nT' -> '260853192], original [submission:217308610]).\n\n\nT'
en6 Английский bitset 2024-05-13 23:04:10 751 Tiny change: 'main() {\n cin.tie(0)' -> 'main() {\n cin.tie(0)'
en5 Английский bitset 2024-05-13 22:52:28 71
en4 Английский bitset 2024-05-13 22:39:57 278 Tiny change: 's I saw:\n- They i' -> 's I saw:\n\n- They i'
en3 Английский bitset 2024-05-13 22:30:54 54
en2 Английский bitset 2024-05-13 22:28:59 325
en1 Английский bitset 2024-05-13 22:24:34 908 Initial revision (saved to drafts)