SVO

[Hicham Mouline]

Hi,
I have data that looks like:

x f(x)
------ ---------
0.5 7.8
0.9 6.7
-5.4 6.6
0.0 6.6
1.5 7.8


The number of points is variable but in the majority of cases is under
MaxSize=16

I used a "small vector optimization" container like

template <typename Traits> // Traits contain the type of x and of f(x) and
MaxSize
class Container {

private:
typedef std:air<double, double> EntryType;
boost::array< EntryType, Traits::MaxSize > mOnStack;
std::vector< EntryType > mOnFreeStore;
};

Container<T> c (...); // constructor with some signature

I will do the brief exercise of implementing this and its iterator and then
test for my use-cases whether it will be faster overall
compared to using a plain vector

In my use cases, I construct my container once and after that do a lot of
[] unchecked accesses.


At some points, rarely, I do

std::sort( c.begin(), c.end(), comparator() );

and

std::lower_bound( c.begin(), c.end(), e );

std::lower_bound requires a forward iterator and therefore an iterator that
is default-constructible.


I tried

template <typename T>
class ContainerIterator { // I templated this to provide the const and
non-const version
ContainerIterator( Container<T>&, size_t currentIndex );
// types and operations....
private:
Container<T>& mContainer;
size_t mIndex;
};

this didn't work because for ContainerIterator to model
random_access_iterator, it needs to provide ContainerIterator().
So I changed the reference to a pointer and set

....
ContainerIterator()
: mContainer(0), mIndex(0)

the problem is that under gcc43/linux
std::lower_bound(c.begin(). c.end(), e) crashes as it tries to access at
some stage elements of the container with the index 0.
I suspect it does so after having used the default constructor.

comments and ideas are welcome,

 

[Vladimir Jovic]

Hicham Mouline wrote:
[BIG CUT]

the problem is that under gcc43/linux
std::lower_bound(c.begin(). c.end(), e) crashes as it tries to access at
some stage elements of the container with the index 0.

Last time I tried that function it worked fine (I am using linux as well).

comments and ideas are welcome,

This might give you an idea:
http://www.parashift.com/c++-faq-lite/how-to-post.html#faq-5.8

 

[Martin Eisenberg]

this didn't work because for ContainerIterator to model
random_access_iterator, it needs to provide ContainerIterator().
So I changed the reference to a pointer and set

...
ContainerIterator()
: mContainer(0), mIndex(0)

the problem is that under gcc43/linux
std::lower_bound(c.begin(). c.end(), e) crashes as it tries to
access at some stage elements of the container with the index 0.
I suspect it does so after having used the default constructor.

A default-constructed iterator is allowed to be singular. Have you
forgotten to copy/assign the container pointer member?


Martin

 

[Hicham Mouline]

A default-constructed iterator is allowed to be singular. Have you
forgotten to copy/assign the container pointer member?

Yep, in the assign operator, not the copy ctor
Thanks for that.