/*
 * Help Access Library 
 * A Library to access the contents of Windows Help files.
 *
 * Copyright (C) 1995-2000 Bernd Herd, http://www.herdsoft.com
 *                                                                  
 * This program is free software; you can redistribute it and/or    
 * modify it under the terms of the GNU General Public License as   
 * published by the Free Software Foundation; either version 2 of   
 * the License.              
 *                                                                  
 * This program is distributed in the hope that it will be useful,  
 * but WITHOUT ANY WARRANTY; without even the implied warranty of   
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the    
 * GNU General Public License for more details.                     
 *                                                                  
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software      
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.        
 */
/* HASH.C ---------------------------------------------
 *
 * @doc
 * @module HASH.C |
 * Computes the Hash-Code for a given Context-String.
 *
 * ISTOPIC-Project.
 *
 *-----------------------------------------------------*/

#include <windows.h>
#include <windowsx.h>
#include <time.h>
#include <stdio.h>
#include <string.h>
#include "hlpacces.h"


#define FAKTOR 0x2B

void    LOCAL nNameForHash(LPSTR buf, DWORD Hash);


/* @func DWORD | HlpGenerateHashValue |
 *
 * Computes a Hash-Value representing a Context-String (#-Footnote) using
 * the same algorithm Windows Help uses internally.
 *
 * @rdesc The 32-Bit Hash Value
 * @parm  LPCSTR | lpszHashString | Pointer to the context-Striong, for example "IDH_CONTENTS"
 */
DWORD WINAPI DLLEXP HlpGenerateHashValue(LPCSTR p)
    {
    static  int  InitFlag = 0;
    static  char MapTable[256];
    DWORD    h = 0;

    if(!InitFlag)   /* set up char translation table */
        {
        int     i;

        for(i = 'A'; i <= 'Z'; ++i)
            MapTable[i] = (i - 'A') + 0x11;
        for(i = 'a'; i <= 'z'; ++i)
            MapTable[i] = (i - 'a') + 0x11;
        for(i = '1'; i <= '9'; ++i)
            MapTable[i] = (i - '1') + 0x01;
        MapTable['0']   = 0x0A;
        MapTable['.']   = 0x0C;
        MapTable['_']   = 0x0D;

        InitFlag = 1;
        }

    while(*p)
        {
        char    c = MapTable[(unsigned char) *p++];
        if(!c)
            continue;
        h   = h * FAKTOR + c;
        }
    return h;
    }




static LPCSTR   StartVal[] = { "", "Ind", "con", "ID_", "IDH", "KEY", "ID", "cn", NULL };

/* @func void | HlpCreateStringForHashValue |
 *
 * Creates a String that has the same Hash-Code and can be used
 * to Transfer hash-code data to Winhelp as a context-String
 * for example in JumpId()-Macros and "-i"-command line Parameter.
 *
 * @comm This Function is implemented in a rather slow manner, so
 *       do not call it more often than needed.
 */
void WINAPI DLLEXP HlpCreateStringForHashValue(
        DWORD HashValue,                // @parm Hash-Code that shall be decoded
        LPSTR Buffer)                  // @parm Buffer for the decoded hash-Value. Minimum Size is 20 Bytes.
{ int           StartChar='A';
  BOOL          HashCodeMatch;
  LPCSTR       *StartNext  = StartVal;

    do {
       if (*StartNext)
              strcpy(Buffer, *StartNext++);
         else sprintf(Buffer, "%c", StartChar++);

      nNameForHash(Buffer, HashValue);  // From Hans-Peter Dittrich: Try to find a String for the Hash-Value
      HashCodeMatch = HlpGenerateHashValue(Buffer) == HashValue;
    }
    while (!HashCodeMatch && StartChar <= 'Z');
}




/* HlpNameForHash ----------------------------------------------*
 * From Hans-Peter-Diettrich:                                   *
 * Searches for a string that represents the given Hash-Value   *
 *--------------------------------------------------------------*/
static  BYTE    cQ[] = "\0" "1234567890\0" "._\0\0\0";  // \0 illegal in strings


void    LOCAL nNameForHash(LPSTR buf, DWORD Hash)
{
        DWORD           hsoll    = Hash;
        DWORD           HashCode = HlpGenerateHashValue(buf);

        int     dig0 = strlen(buf);
        int     i, ndig;

        for (ndig = 0; ndig < 15; ++ndig)
        {
                DWORD   l = HashCode;   // hash0;
                for (i = 0; i < ndig; ++i)
                        l *= FAKTOR;
                l = hsoll - l;

                for (i = ndig; --i >= 0; )      // i = 0; i < ndig; ++i)
      {
                        int     c = (int)(l % FAKTOR);  // last char first!
                        if (c > 0x10)
                                c = (c - 0x10) + '@' + ' ';     // ' ' für small!
                        else
         {
                                c = cQ[c];
                                if (!c)
                                        break;
         }
                        buf[i+dig0] = c;
                        l /= FAKTOR;
                }
                if (i < 0 && !l)        // Ziel erreicht
                {
        buf[dig0+ndig] = 0;
//                      if (SendDlgItemMessage(hDlg, L_TEXT, LB_ADDSTRING, 0, (LONG)(LPSTR)buf) < 0)
                                goto    fertig;
                }
        }

        fertig: ;
}