On Sun, 4 Jun 2006 00:37:28 -0500, "Bo Peng" <ben.bob@gmail.com> wrote:
succ.clear(); size_t numblock = m_N/BitSet::bits_per_block; vector<BitSet::block_type> first_blocks(numblock); for(size_t i=0; i<numblock; ++i) first_blocks[i] = rng().randInt(~BitSet::block_type(0)); succ.append(first_blocks.begin(), first_blocks.end()); // last block BitSet::block_type last_block = rng().randInt(~BitSet::block_type(0)); for(size_t i=0; i < m_N - numblock*BitSet::bits_per_block; ++i) { if((last_block >> i) & 0x1) succ.set(numblock*BitSet::bits_per_block+i); }
When I think again about this, the special treatment of the last block is unnecessary, and because succ is already allocated, the following code is clearer:
vector<BitSet::block_type> blocks(succ.num_blocks()); for(size_t i=0; i<blocks.size(); ++i) blocks[i] = rng().randInt(~BitSet::block_type(0)); from_block_range(blocks.begin(), blocks.end(), succ);
I guess more efficiency can only be achieved through block_begin() and block_end() functions so that I can write to the blocks directly. Is this possible?
No, that is intentionally not possible. But you can construct the dynamic_bitset object directly from a suitable iterator range (no need to use an intermediate vector). Just to illustrate the point, this is an example iterator based on boost::iterator_facade. Use it with caution as I wrote it off the top of my head without verifying if it really satisfies all iterator requirements: #include <cstddef> #include "boost/iterator/iterator_facade.hpp" #include "boost/dynamic_bitset.hpp" template<typename v> class rng_iterator_impl : public boost::iterator_facade< rng_iterator_impl<v>, v, boost::random_access_traversal_tag > { std::size_t count; mutable v val; public: rng_iterator_impl(): count(0), val(0) {} explicit rng_iterator_impl(v c): count(c), val(0) { } private: friend class boost::iterator_core_access; value_type& dereference() const { return val=generate(); } bool equal(rng_iterator_impl const& rhs) const { return count == rhs.count; } void increment() { ++count; } void decrement() { --count; } void advance(difference_type n) { count+=n; } difference_type distance_to(rng_iterator_impl const & r) const { return r.count - count; } v generate() const { /* call you generating function here */ } }; typedef boost::dynamic_bitset<> my_bitset_type; typedef rng_iterator_impl<my_bitset_type::block_type> rng_iterator; Now, you should be able to do: int main() { const int how_many = 8; rng_iterator it; my_bitset_type b(it, it + how_many); } If the last line in main() gives you problem please replace it with: my_bitset_type b; b.append(it, it + how_many); Cheers. --Gennaro.