mardi 23 avril 2013

I like Javascript .....

I'm not a Javascript expert, but the thing I really like with Javascript and our modern Web-Browser is that they allow you to customize your web exeprience....

Today the 'most important news' for me was that the 1st Thor 2 trailer was release, but while clicking on the link i had in my RSS feed, I got a "da.feedsportal.com" before going on my real target !

Hopefully there is link where you can click on the skip that 'ad'.
So now just let Javascript perform the click for you...

Using greasemonkey (Firefox & Chrome) and the following script, you can skip those 'ad' ...

// ==UserScript==
// @name        Skip feedsportal Add
// @namespace   http://da.feedsportal.com/*
// @match       http://da.feedsportal.com/*
// @grant       none
// @version     1
// ==/UserScript==
(function ()
{ 
    var articleLink = document.getElementsByTagName("a")[1];
    location.href = articleLink;
})();
// ==UserScript==
// @name        Skip feedsportal Add
// @namespace   http://da.feedsportal.com/*
// @match       http://da.feedsportal.com/*
// @grant       none
// @version     1
// ==/UserScript==
(function ()
{ 
    var articleLink = document.getElementsByTagName("a")[1];
    location.href = articleLink;
})();
// ==UserScript==
// @name        Skip feedsportal Add
// @namespace   http://da.feedsportal.com/*
// @match       http://da.feedsportal.com/*
// @grant       none
// @version     1
// ==/UserScript==
(function ()
{ 
    var articleLink = document.getElementsByTagName("a")[1];
    location.href = articleLink;
})();
 // ==UserScript==
// @name        Skip feedsportal Add
// @namespace   http://da.feedsportal.com/*
// @match       http://da.feedsportal.com/*
// @grant       none
// @version     1
// ==/UserScript==
(function ()
{
    var articleLink = document.getElementsByTagName("a")[1];
    location.href = articleLink;
})();

// ==UserScript==
// @name        Skip feedsportal Add
// @namespace   http://da.feedsportal.com/*
// @match       http://da.feedsportal.com/*
// @grant       none
// @version     1
// ==/UserScript==
(function ()
{ 
    var articleLink = document.getElementsByTagName("a")[1];
    location.href = articleLink;
})();
// ==UserScript==
// @name        Skip feedsportal Add
// @namespace   http://da.feedsportal.com/*
// @match       http://da.feedsportal.com/*
// @grant       none
// @version     1
// ==/UserScript==
(function ()
{ 
    var articleLink = document.getElementsByTagName("a")[1];
    location.href = articleLink;
})();
// ==UserScript==
// @name        Skip feedsportal Add
// @namespace   http://da.feedsportal.com/*
// @match       http://da.feedsportal.com/*
// @grant       none
// @version     1
// ==/UserScript==
(function ()
{ 
    var articleLink = document.getElementsByTagName("a")[1];
    location.href = articleLink;
})();

lundi 22 avril 2013

Provide your own allocator for std::vector or boost storage

If you plan to write some optimized code (SIMD code like SSE or MMX) using memory coming from a standard container (std::vector or boost::numeric::ublas::unbounded_array), your may be interested by the following.


#include <stdlib.h>//linux aligned malloc
#include <malloc.h>
#if defined(WIN32) || defined(WIN64)
#define simd_alloc(alignment, len) _aligned_malloc(len, alignment)
#define simd_free _aligned_free
#else
#define simd_alloc(alignment, len) memalign(alignment, len)
#define simd_free free
#endif

template<typename T>
class aligned_allocator : public std::allocator<T>
{
public:
void deallocate(pointer _Ptr, size_type)
{ // deallocate object at _Ptr, ignore size
simd_free(_Ptr);
}

pointer allocate(size_type _Count)
{ // allocate array of _Count elements
return (T*)simd_alloc(16, _Count*sizeof(T));
}
};



using that allocator class, you can create a vector like:


template struct myType
{
typedef boost::numeric::ublas::vector<T, boost::numeric::ublas::unbounded_array<T, aligned_allocator<T> > > boost_vector;
typedef std::vector<T, aligned_allocator<T> > std_vector;
};

vendredi 19 avril 2013

An interview question

I had an job interview, and the interviewer had a cool technical and language agnostic question.... He just put the focus on algorithms and their complexity.

The problem was: What is the original complexity of the following function, how to optimize it and what is the resulting complexity.

The function was a common box filter where each output pixel is the sum of the each input pixel around him in a KxK area. And just add some 'noise' in the reflexion he said that the 2-dimensional image was a WxH plane.

So let use some math notation to express that:

P '( x , y ) = i = k 2 k 2 j = k 2 k 2 P ( x + i , y + j )

Looking at that formula, the complexity is clearly O( k 2 ).

Now let express P' iteratively:
P '( x + 1 , y ) = i = k 2 k 2 j = k 2 k 2 P ( x + i , y + j ) + j = k 2 k 2 P ( x + 1 + k 2 , y + j ) j = k 2 k 2 P ( x k 2 , y + j )   
or ....
P '( x + 1 , y )   =   P '( x , y ) + j = k 2 k 2 P ( x + 1 + k 2 , y + j ) j = k 2 k 2 P ( x k 2 , y + j )   

So now the complexity is O(2k)! and if you use a k-vector store the sum of each column, and use that sliding window process, a correct implementation will be in O(k+1)




How to check if an executable is 32bit or 64bit

On windows, using dumpbin.exe what you should have in your PATH if you launch a Visual studio command line or if you run the vsvars.bat ("C:\Program Files (x86)\Microsoft Visual Studio 9.0\Common7\Tools\vsvars32.bat")

>dumpbin.exe path_to_executable.exe /HEADERS

And on linux, just use file

>file path_to_executable

samedi 6 avril 2013

Google API is really easy to use ....

2 weeks ago i spend 1 or 2 hour looking how work the Google Map API (http://hpneo.github.io/gmaps/). The Example page provide helpful piece of code as below.
I put the map focus somewhere .... using latitude and longitude coordinate (48.13199070073399, -1.6228169202804565).







jeudi 31 janvier 2013

Debugging Tips: Exporting a bunch of memory without instrumenting thecode!

Context and problem:

In the last 3 weeks, I worked on aligning a C/C++ code with its Matlab equivalent. During that task I came across the following problem.... I had to compare the data and the program state from C/C++ and Matlab code during 2 parallel debugging session,. So how can we debug and save at any time a C++ vector as binary file without adding noisy instrumentation code?

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std::vector<double> vec(10);
std::ofstream output("out.bin", std::ios::binary|std::ios::out);
output.write(reinterpret_cast<char*>(&vec[0]), vec.size()*sizeof(vec[0]));
output.close();


 And when the file is ready, write in Matlab (for example):
vec_from_c_code = read(open('out.bin'), 'double');
sum(abs(vec_from_c_code - vec_in_matlab))

It could be a debugger feature:

That's why as usual, I first googled it, but I didn't find something ready to use.....

I used Visual Studio 2008 IDE to develop and debug, and it's a really good tools, but it doesn't contain that feature. Using the "memory windows" developer can just see the program memory in hexadecimal and eventually copy a part of it as Text.

With WinDbg, you should have access to a ".writemem" function, and it looks like some extension for VS'2010 to support that syntax from the "Immediate console".... So if its your case, search on http://visualstudiogallery.msdn.microsoft.com/

In another hand Matlab come with an API to directly feed in realtime data from C/C++ (and maybe others languages) in a Matlab session for vizualisation, etc.... But it's something I would found in a production code.

So I build it by myself based on some informations found in the previous page, my own command line.

A solution:

The code below is a simple usage of the 2 function win32 API, OpenProcess and ReadProcessMemory (more details on MSDN). I call this tool a ProcessMemDumper....  evolutions of this code, using a Write function can be made to replace the memory of the program with data coming from file during a debugging session.
Using your debugger, your are going step-by-step through your program, you found for example a "std::vector vec;" that you want to see in another tools (Matlab in my case). You need 3 things, pickup from a simple debugger watch:
  • the offset in the process memory , &vec[0],
  • and the number of bytes, vec size * 8(size of double)
Also get the process PID, and  call from a command line:
  • processmemdumper.exe PID offset nbbytes  out.bin
 Really more efficient than adding export source code everywhere....

Source code:

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// ProcessMemDumper.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"

#include <windows.h>

#include <string>
#include <iostream>
#include <fstream>
#include <vector>
#include <stdexcept>
#include <sstream>

#include "boost/shared_ptr.hpp"

void delete_HANDLE(HANDLE p) 
{ 
  std::cout << "Releasing Handle ...." << std::endl;
  CloseHandle(p);  
};


int _tmain(int argc, _TCHAR* argv[])
{
 try
 {
  unsigned int procPID = atoi(argv[1]);
  std::string procAddressHexa = std::string(argv[2]);
  std::stringstream hexToInt;
  hexToInt << std::hex << procAddressHexa;
  unsigned int procAddress = 0;
  hexToInt >> procAddress;
  unsigned int nbbytetoRead = atoi(argv[3]);
  std::string targetFileName = std::string(argv[4]);

  boost::shared_ptr<void> procHandle(OpenProcess(PROCESS_VM_READ, false, DWORD(procPID)), &::delete_HANDLE);
  if(procHandle)
  {
   std::vector<char> memCopyofProcMem(nbbytetoRead);

   SIZE_T NumberOfBytesRead = 0;
   if(ReadProcessMemory(procHandle.get(), LPCVOID(procAddress), LPVOID(&memCopyofProcMem[0]), SIZE_T(nbbytetoRead), &NumberOfBytesRead) && NumberOfBytesRead == nbbytetoRead)
   {
    std::ofstream targetFile(targetFileName, std::ios::binary|std::ios::out);
    targetFile.write(&memCopyofProcMem[0], nbbytetoRead);
    targetFile.close();
   }
   else
   {
    std::cout << "ReadProcessMemory return false, or NumberOfBytesRead != of the requested number of byte." << std::endl;
    return -1;
   }
  } 
 }
 catch (const std::exception& e)
 {
  std::cout << "std::exception: " << e.what() << std::endl;
  return -1;
 }
 catch (...)
 {
  std::cout << "unknown exception: " << std::endl;
  return -1;
 }
 return 0;
}

mercredi 19 décembre 2012

The annoying push_back.....

Maybe you know, but maybe not,
but one of the really nice feature coming in the C++11 standard is the "initializer list".

In fact with C++11, you can now write:
std:vector vec = {"blog", "msg"};

see http://en.wikipedia.org/wiki/C%2B%2B11#Core_language_usability_enhancements

But if you are still using the old C++, you can at least try to avoid the push_back usage...

Instead of writing

std:vector vec;
vec.push_back("blog");
vec.push_back("msg");

let's use Boost/Assign to offer a += operator supporting variable number of arguments

#include "boost/assign.hpp"
std:vector vec;
vec += "blog", "msg";