C / C++ / MFC Discussion Boards

crc32 here and here

this crc32 ?

Lookup tables are fast.

how table will be fast?

http://en.wikipedia.org/wiki/Lookup_table says:
A Lookup table is a data structure, usually an array or associative array,
often used to replace a runtime computation with a simpler array indexing operation.
The savings in terms of processing time can be significant, since retrieving a value from memory
is often faster than undergoing an 'expensive' computation or calculation operation.

For example this is regularly done as part of CRC calculations.

C#

#include <iostream.h>



// The CRC lookup table  size is  8x32=256
const static unsigned int table[] =
{
    0x000000000, 0x077073096, 0x0EE0E612C, 0x0990951BA, 0x0076DC419, 0x0706AF48F, 0x0E963A535, 0x09E6495A3,
    0x00EDB8832, 0x079DCB8A4, 0x0E0D5E91E, 0x097D2D988, 0x009B64C2B, 0x07EB17CBD, 0x0E7B82D07, 0x090BF1D91,
    0x01DB71064, 0x06AB020F2, 0x0F3B97148, 0x084BE41DE, 0x01ADAD47D, 0x06DDDE4EB, 0x0F4D4B551, 0x083D385C7,
    0x0136C9856, 0x0646BA8C0, 0x0FD62F97A, 0x08A65C9EC, 0x014015C4F, 0x063066CD9, 0x0FA0F3D63, 0x08D080DF5,
    0x03B6E20C8, 0x04C69105E, 0x0D56041E4, 0x0A2677172, 0x03C03E4D1, 0x04B04D447, 0x0D20D85FD, 0x0A50AB56B,
    0x035B5A8FA, 0x042B2986C, 0x0DBBBC9D6, 0x0ACBCF940, 0x032D86CE3, 0x045DF5C75, 0x0DCD60DCF, 0x0ABD13D59,
    0x026D930AC, 0x051DE003A, 0x0C8D75180, 0x0BFD06116, 0x021B4F4B5, 0x056B3C423, 0x0CFBA9599, 0x0B8BDA50F,
    0x02802B89E, 0x05F058808, 0x0C60CD9B2, 0x0B10BE924, 0x02F6F7C87, 0x058684C11, 0x0C1611DAB, 0x0B6662D3D,
    0x076DC4190, 0x001DB7106, 0x098D220BC, 0x0EFD5102A, 0x071B18589, 0x006B6B51F, 0x09FBFE4A5, 0x0E8B8D433,
    0x07807C9A2, 0x00F00F934, 0x09609A88E, 0x0E10E9818, 0x07F6A0DBB, 0x0086D3D2D, 0x091646C97, 0x0E6635C01,
    0x06B6B51F4, 0x01C6C6162, 0x0856530D8, 0x0F262004E, 0x06C0695ED, 0x01B01A57B, 0x08208F4C1, 0x0F50FC457,
    0x065B0D9C6, 0x012B7E950, 0x08BBEB8EA, 0x0FCB9887C, 0x062DD1DDF, 0x015DA2D49, 0x08CD37CF3, 0x0FBD44C65,
    0x04DB26158, 0x03AB551CE, 0x0A3BC0074, 0x0D4BB30E2, 0x04ADFA541, 0x03DD895D7, 0x0A4D1C46D, 0x0D3D6F4FB,
    0x04369E96A, 0x0346ED9FC, 0x0AD678846, 0x0DA60B8D0, 0x044042D73, 0x033031DE5, 0x0AA0A4C5F, 0x0DD0D7CC9,
    0x05005713C, 0x0270241AA, 0x0BE0B1010, 0x0C90C2086, 0x05768B525, 0x0206F85B3, 0x0B966D409, 0x0CE61E49F,
    0x05EDEF90E, 0x029D9C998, 0x0B0D09822, 0x0C7D7A8B4, 0x059B33D17, 0x02EB40D81, 0x0B7BD5C3B, 0x0C0BA6CAD,
    0x0EDB88320, 0x09ABFB3B6, 0x003B6E20C, 0x074B1D29A, 0x0EAD54739, 0x09DD277AF, 0x004DB2615, 0x073DC1683,
    0x0E3630B12, 0x094643B84, 0x00D6D6A3E, 0x07A6A5AA8, 0x0E40ECF0B, 0x09309FF9D, 0x00A00AE27, 0x07D079EB1,
    0x0F00F9344, 0x08708A3D2, 0x01E01F268, 0x06906C2FE, 0x0F762575D, 0x0806567CB, 0x0196C3671, 0x06E6B06E7,
    0x0FED41B76, 0x089D32BE0, 0x010DA7A5A, 0x067DD4ACC, 0x0F9B9DF6F, 0x08EBEEFF9, 0x017B7BE43, 0x060B08ED5,
    0x0D6D6A3E8, 0x0A1D1937E, 0x038D8C2C4, 0x04FDFF252, 0x0D1BB67F1, 0x0A6BC5767, 0x03FB506DD, 0x048B2364B,
    0x0D80D2BDA, 0x0AF0A1B4C, 0x036034AF6, 0x041047A60, 0x0DF60EFC3, 0x0A867DF55, 0x0316E8EEF, 0x04669BE79,
    0x0CB61B38C, 0x0BC66831A, 0x0256FD2A0, 0x05268E236, 0x0CC0C7795, 0x0BB0B4703, 0x0220216B9, 0x05505262F,
    0x0C5BA3BBE, 0x0B2BD0B28, 0x02BB45A92, 0x05CB36A04, 0x0C2D7FFA7, 0x0B5D0CF31, 0x02CD99E8B, 0x05BDEAE1D,
    0x09B64C2B0, 0x0EC63F226, 0x0756AA39C, 0x0026D930A, 0x09C0906A9, 0x0EB0E363F, 0x072076785, 0x005005713,
    0x095BF4A82, 0x0E2B87A14, 0x07BB12BAE, 0x00CB61B38, 0x092D28E9B, 0x0E5D5BE0D, 0x07CDCEFB7, 0x00BDBDF21,
    0x086D3D2D4, 0x0F1D4E242, 0x068DDB3F8, 0x01FDA836E, 0x081BE16CD, 0x0F6B9265B, 0x06FB077E1, 0x018B74777,
    0x088085AE6, 0x0FF0F6A70, 0x066063BCA, 0x011010B5C, 0x08F659EFF, 0x0F862AE69, 0x0616BFFD3, 0x0166CCF45,
    0x0A00AE278, 0x0D70DD2EE, 0x04E048354, 0x03903B3C2, 0x0A7672661, 0x0D06016F7, 0x04969474D, 0x03E6E77DB,
    0x0AED16A4A, 0x0D9D65ADC, 0x040DF0B66, 0x037D83BF0, 0x0A9BCAE53, 0x0DEBB9EC5, 0x047B2CF7F, 0x030B5FFE9,
    0x0BDBDF21C, 0x0CABAC28A, 0x053B39330, 0x024B4A3A6, 0x0BAD03605, 0x0CDD70693, 0x054DE5729, 0x023D967BF,
    0x0B3667A2E, 0x0C4614AB8, 0x05D681B02, 0x02A6F2B94, 0x0B40BBE37, 0x0C30C8EA1, 0x05A05DF1B, 0x02D02EF8D
};


const int crcSIZE = 5;
class Test
{

    public:
    // The CRC lookup table
    const static unsigned int table[crcSIZE];

    unsigned int GetCRC32(const unsigned char* bytes, const unsigned int len)
    {
        unsigned int crc = 0xFFFFFFFF;
        unsigned char byte=0;

        for(unsigned int i = 0; i < len; i++)
        {
            crc = (crc >> 8) ^ table[byte];
            cout<<crc<<"\t";
        }
        return crc ^ 0xFFFFFFFF;
        }
    };

    const unsigned int Test::table[crcSIZE] =
    {
    0x000000000, 0x077073096, 0x0EE0E612C, 0x0990951BA, 0x0076DC419

};

int main( )
{
    unsigned char bytes[] = { 0xAA, 0xBB, 0xCC };
    Test tst;
    tst.GetCRC32(bytes, 3);
    cout<<"\n";

return 0;
}

I have read through this chain (I was going to say 'string' but that would only confuse the issue)

You have to understand folks here, many are just as curious about the 'why' as about the 'how'. You haven't answered 'why are you doing this?'

To many, myself included, you have embarked on a totally useless exercise. Why in the world would you want a random string of characters that happens to generate the same CRC32 that you already have in your hand? You cannot possible reconstruct the original string so of what interest is a random string with the same CRC32. Unless you are trying to fool some other program who knows the CRC32 of the data it wants and you are trying to pump some junk at it for some amusing or nefarious reason.

So, tell us 'why' you need such a string, you may find some folks who find the problem more interesting than it seems so far.

Chuck O'Toole wrote:
Unless you are trying to fool some other program who knows the CRC32 of the data it wants and you are trying to pump some junk at it for some amusing or nefarious reason.

seems likely, to me.

image processing toolkits | batch image processing

My Aim is to generate a string from know CRC32 value in fastest way.

Having read all the above answers why do you persist in believing this is possible?

Unrequited desire is character building. OriginalGriff

Richard MacCutchan wrote:
Having read all the above answers why do you persist in believing this is
possible?

Head, meet brick wall.

He just doesnt get it. Smile | :)

==============================

Nothing to say.

I got it

. And everything is possible which can be thought...got it... Smile | :)

john5632 wrote:
And everything is possible which can be thought

Good luck with the impossible. Smile | :)

==============================

Nothing to say.

Thanks, I was a bit worried it was me!

Unrequited desire is character building. OriginalGriff

Hi Developers,

We are using third party controls, it's a report control ( I have seen that ultimately it was derived from CWnd class). I am working on a searching functionality and we can select related words to the search query as well.

I have added a "Select All/Unselect All" feature for the words that are related to main search. In my function I am checking/unchecking all the words programatically. Suppose I have checked one or more words manually, after i am selecting all. The application is getting crashed. I am replacing that checked item with the new checked item( having true value ).

One intersting point is that if i am hust clicking on select/deselect all it works perfectaly.

Thanks.
Amrit Agrawal
Software Developer

Did you try and debug upto the point of crash?
It appears that you are trying to read/write from invalid memory locations.
Are you adding and deleting items from the lists that you maintain for checking and unchecking values and performing operations in them?

Please elaborate on the data structure etc that you are using and the operations you perform.

You talk about Being HUMAN. I have it in my name
AnsHUMAN

I have a dialog form, where I have an listctrl. On listcontrol set focus handler, I need to send a click message, like I would click on listcontrol. I try in follow way, but didn't work it

C++

void CMyPage::OnSetfocusListFeature(NMHDR* pNMHDR, LRESULT* pResult) 
{
	// TODO: Add your control notification handler code here

	NMHDR nmh;
	nmh.code = NM_CLICK;
	nmh.idFrom = m_ListFeature.GetDlgCtrlID();
	nmh.hwndFrom = m_hWnd;
	SendMessage(WM_NOTIFY,0,(LPARAM)&nmh);

	*pResult = 0;
}

... can you tell me hat i'm doing wrong ?

nmh.hwndFrom = m_hWnd;

is your problem. it should be the hwnd of of the window of the CONTROL you want to send the message to.

WM_NOTIFY uses the id or the hwnd. if you pass the hwnd, it uses it. So you are sending the WM_NOTIFY to the dialog, not the list child of the dialog.

Thank you, I will try and let you know what I've done.

Now goes. Thanks.

modified 19-Oct-11 3:03am.

If you're trying to select a particular item from the list you can do this-

m_ListFeature.SetItemState(0, LVIS_SELECTED, LVIS_SELECTED);

«_Superman_»
I love work. It gives me something to do between weekends.

Microsoft MVP (Visual C++)

Polymorphism in C

No, I don't want to select an specific item, just to make a virtual click on listcontrol.

Why? Since clicking has the effect of selecting an item selecting it as Superman suggested is superior.

Steve

I open an custom control on listcontrol and this custom control is hidden on clicked anywhere on list ... that's why I need click message and not select an specific item.

This is what I've come up with so far but need to find & add values to the form elements for user input and password input, then submit. I'm using C++Builder6.

#include <mshtml.h>

//
TComInterface<IHTMLDocument2>HTMLDoc;
Browser->Document->QueryInterface(IID_IHTMLDocument2,(LPVOID*)&HTMLDoc);

//get all the forms
TComInterface<IHTMLElementCollection>HTMLforms;
HTMLDoc->get_forms(&HTMLforms);

//Get form 0 since login pages have only one form
TComInterface<IHTMLFormElement>HTMLform;

//Get User,Password fields & set values
TComInterface<IHTMLElement>HTMLfield;

//Then submit form
HTMLform->submit();

Thanks!

I hope this Boland C++ Builder 6 code might work..

C#

#include utilcls.h
#include Mshtml.h

template<class ParentIntf, class ItemIntf>
HRESULT __fastcall GetHTMLItem(ParentIntf *CollectionOrElement, const
WideString &name, ItemIntf** ppIntf)
{
	TVariant vName = name;
	TVariant vIndex = 0;
	TComInterface disp;

	HRESULT hRes = CollectionOrElement->item(vName, vIndex, &disp);
	if( SUCCEEDED(hRes) )
	hRes = disp->QueryInterface(__uuidof(ItemIntf),(LPVOID*)ppIntf);
	return hRes;
}

void __fastcall TForm1::CppWebBrowser1DocumentComplete (TObject*
Sender, LPDISPATCH pDisp, TVariant *URL)
{
	if( CppWebBrowser->Document )
	{
		TComInterface HTMLDoc;
		if(SUCCEEDED(CppWebBrowser->Document->QueryInterface(
		IID_IHTMLDocument2,(LPVOID*)&HTMLDoc) ) )
		{
			TComInterface forms;
			if( SUCCEEDED(HTMLDoc->get_forms(&forms)) )  
			{
				TComInterface form;
				if( SUCCEEDED(GetHTMLItem(forms, "loginform", &form)) )
				{
				TComInterface userid;
				TComInterface password;

				GetHTMLItem(form, "userid", &userid);
				GetHTMLItem(form, "password", &password);

				if( userid )
				userid->put_value(WideString("username"));

				if( password )
				password->put_value(WideString("password"));
				}
			}
		}
	}
}

I hope this Boland C++ Builder 6 code might work too..

bool TForm1::Login(char* inputname, const AnsiString& text)
{
 bool done = false;
 
 IHTMLDocument2* HTMLDoc = NULL;
 
 if(SUCCEEDED(CppWebBrowser1->Document->QueryInterface(IID_IHTMLDocument2,  (LPVOID*)&HTMLDoc)))
{
 IHTMLElementCollection* pAll = NULL;
 if(SUCCEEDED(HTMLDoc->get_all(&pAll)))
 {
   // <input type="text" name="the_tag">
 
   Variant name = inputname;
   Variant index = 0;
 
   IDispatch* pDisp = NULL;
 
   if(SUCCEEDED(pAll->item(name, index, &pDisp)))
   {
    if ( pDisp )
    {
      // IHTMLInputFileElement* pInput = NULL;     // mshtml.h
     IHTMLInputElement* pInput = NULL;     // mshtml.h
      // IHTMLFormElement* pForm = NULL;         // mshtml.h
 
    pDisp->QueryInterface(IID_IHTMLInputElement, (LPVOID*)&pInput);
    pDisp->Release();
 
    if(pInput)
    {
     pInput->put_value(WideString(text));
 
     done = true;
 
      /*
      WideString mybuffer;
      pInput->get_value ( &mybuffer );
      ShowMessage ( mybuffer );
      */
 
     pInput->Release();
     }
    }
   }
    pAll->Release();
  }
 
  HTMLDoc->Release();
 }
  return done;
}