Hello. I am using your dynamic_bitset and I encountered the following problem. I have realy large bits sets (>100000) bits. At some point I need do some xor Operations on only a small fraction of the bits. So I need a way to access the bits from index n to n+s-1. The bitclass has no convient way to do this. I suggest add the member function sub_bitset for that purpose. Example: a = 100000101101101001110101 ^^^^^^^ a.subbitset(3,7) b = 1001110 (The ^^^^^^^ marks the position of b in a). I implemented subbitset as follows: template<typename B, typename A> dynamic_bitset<B, A> dynamic_bitset<B, A>::subbitset(size_type n,size_type s) const { assert(n+s < size()); dynamic_bitset res(s); size_type const last = res.num_blocks() - 1; // num_blocks() is >= 1 size_type const last2 = num_blocks() - 1; size_type const div = n / bits_per_block; // div is <= last block_width_type const r = bit_index(n); const block_type * const b = &m_bits[0]; block_type * const bb = &res.m_bits[0]; if (r != 0) { block_width_type const ls = bits_per_block - r; for (size_type i = 0; i <= last; ++i) { if (div+i+1 >last2) { // Do we reach the last block? bb[i] = (b[div+i] >> r); break; } bb[i] = (b[div+i] >> r) | (b[div+i+1] << ls); } } else { for (size_type i = 0; i <= last; ++i) { if (i+div>last2) // Do we reach the last block? break; bb[i] = b[i+div]; } // note the '<=': the last iteration 'absorbs' // b[last-div] = b[last] >> 0; } // Zero unused bits block_width_type const rr = bit_index(s); if(rr != 0) bb[last] &= (1<<(block_type)(rr))-1; return res; } I guess, that I am not the only one who would benefit from the possibility to access subbitsets. I could also imagine that references to subbitsets could be of some use. Foe example I could imagine that one would use subbitset as follows. a= 00000000 b= 111 a.subbit(2,3) ^= b; -> a=00011100 But such a reference would be harder to implement and at the moment I do not need it. What do you think? Is there any hope for subbitset in boost? Best wishes Andreas Klein.