Re: [Boost-users] set() of dynamic_bitset is too slow.

3 Jun 2006

      On Fri, 2 Jun 2006 17:03:11 -0500, "Bo Peng" 
wrote:
...
Dear list,
I am using dynamic_bitset to store a sequence of random 0/1. The
program generates repeatedly 32bit random numbers and assign the
result to a dynamic_bitset.
for(UINT i=0; i < m_N; ++i)
      		{
      			if(bit == block)			  // generate a block
      			{
      				ri = rng().randInt(m_max);
      				bit = 0;
      			}
      			if((ri >> bit) & 0x1)
      				succ.set(i);
      			bit++;
      	    }
When I profile this program, I surprisingly find out that succ.set(i)
uses >50% of the execution time. Is there anyway I can assign block by
block to dynamic_bitset, or assign sequentially so the position of i
does not have to be calculated each time?
Hi,

you code looks suspect to me. Are you aware it actually yields m_N
bits rather than m_N blocks? Also, I'll assume the dynamic_bitset is
sized in advance. Sticking to the problem, there are many alternative
codings; in particular you could use the iterator-based version of
append, after creating a little iterator class for the random integers
(please, ignore from_block_range() :-)). If that's not suitable for
you might try this:

    typedef UINT block_type;
    boost::dynamic_bitset succ; /* no resizing needed */

    // (assuming m_N is a multiple of the UINT width, i.e. 32)
    for(UINT i=1; i <= m_N / (block + 1); ++i)
    {
        block_type b = /*random...*/;
        succ.append(b);
    }

Please, let us know if this helped.

Cheers,
Gennaro.

--
Genny.

Re: [Boost-users] set() of dynamic_bitset is too slow.

Gennaro Prota