Re: [boost] [dynamic_bitset] Append byte to the less significant end

Subject: Re: [boost] [dynamic_bitset] Append byte to the less significant end
From: Romain CHANU (romainchanu_at_[hidden])
Date: 2010-12-27 07:56:23

Hey Joachim,

Thank you for your help and advices.

I did use the reverse iterators and it works like a charm.

In my case, the bitsets are not really huge so ICL may not be suitable. But
it is good to know :-)

Cheers,

Romain

On 24 December 2010 23:00, Joachim Faulhaber <afojgo_at_[hidden]> wrote:

> Merry Christmas, Romain :)
>
> 2010/12/24 Romain CHANU <romainchanu_at_[hidden]>:
> > Here is my problem: i am using boost::dynamic_bitset and I would like to
> > append a byte to the bitset.
> >
> > The idea is the following:
> >
> > 1) read a byte (represented as an unsigned char)
> > 2) append the byte to the bitset
> > 3) repeat these steps until there is no more data to read
> >
> > The current "append" in the API appends a byte to the most significant
> end.
> > I would like to actually append the byte to the less significant end.
>
> I think you are trying to use the data structure, dynamic_bitset in a
> way that it was not designed for. Class templates bitset and
> dynamic_bitset are ususally interpreted in two ways.
>
> (1) As sets of elements, represented by bits.
> (2) As a binary number with binary digits starting from the least to
> the most significant bit.
>
> Of the two concepts, set and binary number, the set concept is the
> more important one. It gives the class template its name: bit*set*.
> The operation that you are intending to apply is not a simple append
> of elements, because it always changes the whole set. All elements
> that are in the set already have to be added a value of 8. Then you
> are setting some of the first 8 values from your new byte.
> Dynamic_bitset::append does not alter the elements in the the bitset
> and cheaply adds a new block, containing some new elements, at the
> end.
>
> I'd say you could collect your single bytes (bitsets) in a vector,
> appending them at the end with push_back and then populate a
> dynamic_bitset in reverse order using BlockIterators.
>
> As an alternative to dynamic_bitsets you could also use
> icl::interval_bitsets form the extended Interval Container Library
> ICL+. Class template icl::interval_bitset can represent very lare
> bitsets in a compact form because it uses a combination of interval
> compression and bit compression. You can find examples and an
> introductory implementation here:
>
>
> http://www.joachim-faulhaber.de/boost_icl/doc/libs/icl/doc/html/boost_icl/projects.html#boost_icl.projects.large_bitset
>
> Note, that icl::interval_bitset is not yet a part of the Interval
> Container Library [Boost.Icl] that will be available with the next
> Boost release 1.46. But you can download ICL+ from sourceforge:
>
> http://sourceforge.net/projects/itl/
>
> or get a copy via SVN from the sandbox
>
> https://svn.boost.org/svn/boost/sandbox/icl/
>
> I am planning to add icl::interval_bitsets to the core library
> [Boost.Icl] next and will also add functions for the addition/deletion
> of blocks (elementary bitsets).
>
> HTH
> Joachim
>
> --
> Interval Container Library [Boost.Icl]
> http://www.joachim-faulhaber.de
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