CRCtextDlg.cpp

Return to 32 Bit CRC Text Calculation

// CRCtextDlg.cpp : implementation file
//
// Copyright © 2000 - 2008 Richard A. Ellingson
// http://www.createwindow.com
// mailto:CreateWindow.com@comcast.net

#include "stdafx.h"
#include "CRCtext.h"
#include "CRCtextDlg.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif

/////////////////////////////////////////////////////////////////////////////
// CAboutDlg dialog used for App About

class CAboutDlg : public CDialog
{
public:
     CAboutDlg();

// Dialog Data
     //{{AFX_DATA(CAboutDlg)
     enum { IDD = IDD_ABOUTBOX };
     //}}AFX_DATA

     // ClassWizard generated virtual function overrides
     //{{AFX_VIRTUAL(CAboutDlg)
     protected:
     virtual void DoDataExchange(CDataExchange* pDX); // DDX/DDV support
     //}}AFX_VIRTUAL

// Implementation
protected:
     //{{AFX_MSG(CAboutDlg)
     //}}AFX_MSG
     DECLARE_MESSAGE_MAP()
};

CAboutDlg::CAboutDlg() : CDialog(CAboutDlg::IDD)
{
     //{{AFX_DATA_INIT(CAboutDlg)
     //}}AFX_DATA_INIT
}

void CAboutDlg::DoDataExchange(CDataExchange* pDX)
{
     CDialog::DoDataExchange(pDX);
     //{{AFX_DATA_MAP(CAboutDlg)
     //}}AFX_DATA_MAP
}

BEGIN_MESSAGE_MAP(CAboutDlg, CDialog)
     //{{AFX_MSG_MAP(CAboutDlg)
          // No message handlers
     //}}AFX_MSG_MAP
END_MESSAGE_MAP()

/////////////////////////////////////////////////////////////////////////////
// CCRCtextDlg dialog

CCRCtextDlg::CCRCtextDlg(CWnd* pParent /*=NULL*/)
     : CDialog(CCRCtextDlg::IDD, pParent)
{
     //{{AFX_DATA_INIT(CCRCtextDlg)
     m_csURL = _T("");
     //}}AFX_DATA_INIT
     // Note that LoadIcon does not require a subsequent DestroyIcon in Win32
     m_hIcon = AfxGetApp()->LoadIcon(IDR_MAINFRAME);
}

void CCRCtextDlg::DoDataExchange(CDataExchange* pDX)
{
     CDialog::DoDataExchange(pDX);
     //{{AFX_DATA_MAP(CCRCtextDlg)
     DDX_Control(pDX, IDC_CRCTEXT, m_ctlCRC);
     DDX_Control(pDX, IDC_TEXT, m_ctlTextEdit);
     DDX_Text(pDX, IDC_URL, m_csURL);
     //}}AFX_DATA_MAP
}

BEGIN_MESSAGE_MAP(CCRCtextDlg, CDialog)
     //{{AFX_MSG_MAP(CCRCtextDlg)
     ON_WM_SYSCOMMAND()
     ON_WM_PAINT()
     ON_WM_QUERYDRAGICON()
     ON_BN_CLICKED(IDC_RESET, OnReset)
     ON_EN_CHANGE(IDC_TEXT, OnChangeText)
     //}}AFX_MSG_MAP
END_MESSAGE_MAP()

/////////////////////////////////////////////////////////////////////////////
// CCRCtextDlg message handlers

BOOL CCRCtextDlg::OnInitDialog()
{
     CDialog::OnInitDialog();

     // Add "About..." menu item to system menu.

     // IDM_ABOUTBOX must be in the system command range.
     ASSERT((IDM_ABOUTBOX & 0xFFF0) == IDM_ABOUTBOX);
     ASSERT(IDM_ABOUTBOX < 0xF000);

     CMenu* pSysMenu = GetSystemMenu(FALSE);
     if (pSysMenu != NULL)
     {
          CString strAboutMenu;
          strAboutMenu.LoadString(IDS_ABOUTBOX);
          if (!strAboutMenu.IsEmpty())
          {
               pSysMenu->AppendMenu(MF_SEPARATOR);
               pSysMenu->AppendMenu(MF_STRING, IDM_ABOUTBOX, strAboutMenu);

               // ******* Begin custom code *******

               // We have a Minimize box on the dialog, but we don't want
               // the Size and Maximize options on the system menu so disable them.
               pSysMenu->EnableMenuItem(SC_SIZE, MF_GRAYED);
               pSysMenu->EnableMenuItem(SC_MAXIMIZE, MF_GRAYED);

               // ******* End custom code *******
          }
     }

     // Set the icon for this dialog. The framework does this automatically
     // when the application's main window is not a dialog
     SetIcon(m_hIcon, TRUE);               // Set big icon
     SetIcon(m_hIcon, FALSE);          // Set small icon

     // TODO: Add extra initialization here

// ******* Begin custom code *******

     // Don't forget to create the lookup table first
     Init_CRC32_Table();

     // Limit the maximum text for the edit box,
     // just so we don't crash if the user tries
     // to dump too much in there.
     m_ctlTextEdit.SetLimitText(50000);
     // Display a warning about NULL characters.
     m_ctlTextEdit.SetWindowText("NULL characters pasted here cause false CRC values");
     // Send the Create Window URL to the dialog
     m_csURL = "http://www.createwindow.com";
     UpdateData(FALSE);

// ******* End custom code *******

     return TRUE; // return TRUE unless you set the focus to a control
}

void CCRCtextDlg::OnSysCommand(UINT nID, LPARAM lParam)
{
     if ((nID & 0xFFF0) == IDM_ABOUTBOX)
     {
          CAboutDlg dlgAbout;
          dlgAbout.DoModal();
     }
     else
     {
          CDialog::OnSysCommand(nID, lParam);
     }
}

// If you add a minimize button to your dialog, you will need the code below
// to draw the icon. For MFC applications using the document/view model,
// this is automatically done for you by the framework.

void CCRCtextDlg::OnPaint()
{
     if (IsIconic())
     {
          CPaintDC dc(this); // device context for painting

          SendMessage(WM_ICONERASEBKGND, (WPARAM) dc.GetSafeHdc(), 0);

          // Center icon in client rectangle
          int cxIcon = GetSystemMetrics(SM_CXICON);
          int cyIcon = GetSystemMetrics(SM_CYICON);
          CRect rect;
          GetClientRect(&rect);
          int x = (rect.Width() - cxIcon + 1) / 2;
          int y = (rect.Height() - cyIcon + 1) / 2;

          // Draw the icon
          dc.DrawIcon(x, y, m_hIcon);
     }
     else
     {
          CDialog::OnPaint();
     }
}

// The system calls this to obtain the cursor to display while the user drags
// the minimized window.
HCURSOR CCRCtextDlg::OnQueryDragIcon()
{
     return (HCURSOR) m_hIcon;
}
// Everything above this line is AppWizard generated code
// except for a few lines in OnInitDialog()

// ******* Begin custom code *******

// Handler for Close program messages
void CCRCtextDlg::OnCancel()
{
     // TODO: Add extra cleanup here

     // I like to override this function so the dialog
     // doesn't close when the Escape key is pressed.
     if(GetKeyState(VK_ESCAPE) & 128)
          return;

     CDialog::OnCancel();
}

// Handler for the Reset button
void CCRCtextDlg::OnReset()
{
     // TODO: Add your control notification handler code here

     // Reset the CRC value
     m_ctlCRC.SetWindowText("0");
     // Empty the edit box
     m_ctlTextEdit.SetWindowText("");
     // Set focus to the Edit box
     m_ctlTextEdit.SetFocus();

}

// Handler for when the user changes the text in the edit box.
void CCRCtextDlg::OnChangeText()
{// Called by Windows when text changes

     // TODO: Add your control notification handler code here

     CString csText;
     int nCRC;
     char chCRC[8];

     // Get the text from the edit box.
     // Note that we can't handle NULL characters that the user might
     // paste into the Edit box because the text string terminates
     // at the first NULL character.
     m_ctlTextEdit.GetWindowText(csText);
     // Pass the text string to Get_CRC().
     // The return value is a CRC integer.
     nCRC = Get_CRC(csText);
     // Convert the integer to an ASCII character string.
     itoa(nCRC, chCRC, 16); // Note that the CRC number is in hex
     // Set the CRC string in the sunken static box on the dialog.
     m_ctlCRC.SetWindowText(chCRC);

}

// Call this function only once to initialize the CRC table.
void CCRCtextDlg::Init_CRC32_Table()
{// Called by OnInitDialog()

     // This is the official polynomial used by CRC-32
     // in PKZip, WinZip and Ethernet.
     ULONG ulPolynomial = 0x04c11db7;

     // 256 values representing ASCII character codes.
     for(int i = 0; i <= 0xFF; i++)
     {
          crc32_table[i]=Reflect(i, 8) << 24;
          for (int j = 0; j < 8; j++)
               crc32_table[i] = (crc32_table[i] << 1) ^ (crc32_table[i] & (1 << 31) ? ulPolynomial : 0);
          crc32_table[i] = Reflect(crc32_table[i], 32);
     }
}

// Reflection is a requirement for the official CRC-32 standard.
// You can create CRCs without it, but they won't conform to the standard.
ULONG CCRCtextDlg::Reflect(ULONG ref, char ch)
{// Used only by Init_CRC32_Table()

     ULONG value(0);

     // Swap bit 0 for bit 7
     // bit 1 for bit 6, etc.
     for(int i = 1; i < (ch + 1); i++)
     {
          if(ref & 1)
               value |= 1 << (ch - i);
          ref >>= 1;
     }
     return value;
}

// Once the lookup table has been filled in by the two functions above,
// this function creates all CRCs using only the lookup table.
int CCRCtextDlg::Get_CRC(CString &text)
{// Called by OnChangeText()

     // Be sure to use unsigned variables,
     // because negative values introduce high bits
     // where zero bits are required.

     // Start out with all bits set high.
     ULONG ulCRC(0xffffffff);
     int len;
     unsigned char* buffer;

     // Get the length.
     // Note that if the text contains NULL characters
     // processing ends at the first NULL and the CRC value is invalid.
     // See the 32 Bit File Demonstration source code
     // for a method of dealing with NULL characters in files.
     len = text.GetLength();
     // Save the text in the buffer.
     buffer = (unsigned char*)(LPCTSTR)text;
     // Perform the algorithm on each character
     // in the string, using the lookup table values.
     while(len--)
          ulCRC = (ulCRC >> 8) ^ crc32_table[(ulCRC & 0xFF) ^ *buffer++];
     // Exclusive OR the result with the beginning value.
     return ulCRC ^ 0xffffffff;
}
// ******* End custom code *******