The most efficient method to change the value of a

问题:

I need an efficient method with low complexity to change the values of a range of bits in the bitset :

bitset<1000000> bs;

and I need to set values from 100 to 500 to TRUE for example .

what is the fastest method to accomplish this in the lowest complexity ?

using a loop wouldn't suffice for sure .

回答1:

An ordinary for-loop is the easiest and fastest way:

std::bitset<1000000> bs;

for (unsigned i = start, stop = start + n; i != stop; ++i)
  bs.set(i);

Unfortunately:

• given the size of bs, working with masks / shifting isn't an option (e.g. see in bitset, can i use "to_ulong" for a specific range of bits?)
• the interface of bitset doesn't support ranges / sub-blocks (e.g. What is the performance of std::bitset?). The same limitation is present in boost::dynamic_bitset.

Also consider that std::bitset doesn't come with iterators, so it cannot be used with the functions in <algorithm> library.

If performance really matters you could consider an ad-hoc implementation.