Re: [boost] Google Summer Of Code

Subject: Re: [boost] Google Summer Of Code
From: vicente.botet (vicente.botet_at_[hidden])
Date: 2010-03-18 14:05:47

----- Original Message ----- 
From: "Brian Bartman" <bbartmanboost_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Thursday, March 18, 2010 2:45 PM
Subject: [boost] Google Summer Of Code

> 
> Hello my name is Brian Bartman and I am an undergraduate at Kent State
> University Majoring in computer science.
> 
> I was interested in the bits & ints project, specifically Compressed array
> and Compressed vector as well as the utilities for bit mask manipulation.
> 
> Could some one help me better understand the requirements of this project?
> I would like to draft a proposal for GSoC 2010 and wanted to better
> understand the project before I write a proposal.

Hello,

I don't know if you are interested in improving Boost.Bitfield. I had two features I wanted to add since long time but I had not time lastly finish them. You can find information related to Boost.Bitfield in https://svn.boost.org/trac/boost/wiki/LibrariesUnderConstruction#Boost.Bitfield.

The two features are:
* Add bitfields group 
Used to easily manipulate groups of bitfields the same way as does C bitfields, but in a portable manner. Example declaration: 
struct Rgb565
{
    struct red {};
    struct green {};
    struct blue {};
    typedef bitfields<
            member<unsigned char, red,   5>,
            member<unsigned char, green, 6>,
            member<unsigned char, blue,  5> 
    > type; 
};

Example usage: 
Rgb565::type r = make_bitfields<Rgb565::type, 1,2,3>;

// Write to a bitfield.
r.get<Rgb565::red>() = 23;
//or
r.set<Rgb565::red>(23);

// Read from a bitfield
Rgb565::at<Rgb565::blue>::value_type b = r.get<Rgb565::blue>();

Other posibility could be to use unamed bitfields whic are accessed as tuples. 
typedef bitfields_group<5,6,5 > Rgb565; 
Rgb565 r;

r.get<0>() = 23;
// or
r.set<0>(23);

// Read from a bitfield
Rgb565::at<2>::value_type b = r.get<2>();

* Add pointer_plus_bits 
Based on 
- the article of Joaquin Optimizing red-black tree color bits (http://bannalia.blogspot.com/2008/11/optimizing-red-black-tree-color-bits.html), 
- the implementation of Ion pointer_plus_bits from Boost.Intrusive (http://www.boost.org/boost/boost/intrusive/pointer_plus_bits.hpp) , and 
- Clang's QualType smart pointer (Clang's QualType smart pointer)

This class will allows to use the unsused bits of a pointer to reduce the size of the nodes containing pointers and bits and sometimes improving also the performances. 
I have not reached yet the interface I would like to have. For the moment we can do 
typedef pointer_plus_bits<int*,1,bool>::type pint_and_bool;

int i=0;
pint_and_bool v1;
ASSERT_EQUALS(v1.pointer(),0);
ASSERT_EQUALS(v1.small_int(),false);
pint_and_bool v2(&i, true);
ASSERT_EQUALS(v2.pointer(),&i);
ASSERT_EQUALS(v2.small_int(),true);
v1.pointer()=v2.pointer();
v1.small_int()=true;
ASSERT_EQUALS(v1.pointer(),&i);
ASSERT_EQUALS(v1.small_int(),true);

typedef pointer_plus_bits<
        pointer_plus_bits<int*,1,bool>::type
                        ,1, bool>::type  pint_and_bool_bool
pint_and_bool_bool v1;
ASSERT_EQUALS(v1.small_int(),false);
ASSERT_EQUALS(v1.pointer().get_pointer(),0);
ASSERT_EQUALS(v1.get_pointer().get_pointer(),0);
ASSERT_EQUALS(v1.get_pointer().small_int(),false);

Let me know if this is related to what you are interested in.

best,
Vicente