计算std :: vector< bool>中的设置值 [英] Counting set values in std::vector<bool>

问题描述

std :: vector< bool> 是否使用 POPCNT 指令来计算 std :: count 算法的结果?

Does std::vector<bool> use POPCNT instruction to compute the result of std::count algorithm?

如果否，是否可以在不复制粘贴整个向量的情况下实现?为此，我需要访问实际存储在该向量中的 unsigned int 值，有可能吗?

If no, is it possible to implement without copy-pasting the complete vector? To do that, I need to access unsigned int values actually stored in that vector, is it possible?

如果有问题，我只需要VC ++ 2017解决方案.

If it matters, I only need VC++ 2017 solution.

推荐答案

std :: count 不对 std :: vector< bool>使用 popcnt ; (不幸的是，至少在GNU C ++标准库中).

std::count doesn't use popcnt for std::vector<bool> unfortunately (at least with GNU C++ standard library).

std :: vector< bool> 也不提供对其原始存储的访问， std :: vector< bool> :: data 返回 void.

std::vector<bool> doesn't provide access to its raw storage either, std::vector<bool>::data returns void.

另一种解决方案是使用 boost :: dynamic_bitset<> . boost :: dynamic_bitset<> :: count 使用 popcnt 指令，请参见汇编输出.

An alternative solution is to use boost::dynamic_bitset<>. boost::dynamic_bitset<>::count uses popcnt instruction, see assembly output.

GNU C ++ std :: vector< bool> 是次优实现的，其大小为40个字节.而 sizeof(boost :: dynamic_bitset<>)是32.

GNU C++ std::vector<bool> is implemented sub-optimally and its size is 40 bytes. Whereas the sizeof(boost::dynamic_bitset<>) is 32.

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