/*
 * $Id$
 */

/*
 * Harbour Project source code: 
 *   ADDASCII() CT3 string function
 *
 * Copyright 2001 IntTec GmbH, Neunlindenstr 32, 79106 Freiburg, Germany
 *        Author: Martin Vogel <vogel@inttec.de>
 *
 * www - http://www.harbour-project.org
 *
 * 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, or (at your option)
 * any later version.
 *
 * 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 software; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
 * Boston, MA 02111-1307 USA (or visit the web site http://www.gnu.org/).
 *
 * As a special exception, the Harbour Project gives permission for
 * additional uses of the text contained in its release of Harbour.
 *
 * The exception is that, if you link the Harbour libraries with other
 * files to produce an executable, this does not by itself cause the
 * resulting executable to be covered by the GNU General Public License.
 * Your use of that executable is in no way restricted on account of
 * linking the Harbour library code into it.
 *
 * This exception does not however invalidate any other reasons why
 * the executable file might be covered by the GNU General Public License.
 *
 * This exception applies only to the code released by the Harbour
 * Project under the name Harbour.  If you copy code from other
 * Harbour Project or Free Software Foundation releases into a copy of
 * Harbour, as the General Public License permits, the exception does
 * not apply to the code that you add in this way.  To avoid misleading
 * anyone as to the status of such modified files, you must delete
 * this exception notice from them.
 *
 * If you write modifications of your own for Harbour, it is your choice
 * whether to permit this exception to apply to your modifications.
 * If you do not wish that, delete this exception notice.
 *
 */


#include "ct.h"


/*  $DOC$
 *  $FUNCNAME$
 *      ADDASCII()
 *  $CATEGORY$
 *      CT3 string functions
 *  $ONELINER$
 *      Add an integer value to an ascii value of a string
 *  $SYNTAX$
 *      ADDASCII (<[@]cString>, <nValue>, [<nPosition>], [<lCarryOver>]) --> cString
 *  $ARGUMENTS$
 *      <[@]cString>   is the string that should be edited
 *      <nValue>       is a integer value that should be added to the
 *                     ASCII value of the character at the <nPosition>th position
 *      [<nPosition>]  is the position of the character that should be edited.
 *                     If not supplied, the last character of <[@]cString> is
 *                     edited.
 *      [<lCarryOver>] NEW: is set to .T. if the substring from position 1 to
 *                     position <nPosition> should be treated as an integer
 *                     written to the base 256. Thus, the addition of <nValue>
 *                     can affect to whole substring (see EXAMPLES).
 *                     Default is .F., the original behaviour of this function.
 *  $RETURNS$
 *      The edited string is returned. The return value can be suppressed by
 *      using the CSETREF() function. The string must then be passed by
 *      reference [@].
 *  $DESCRIPTION$
 *      ADDASCII() can be used to add or subtract integer values from
 *      ASCII values in a string. The new <lCarryOver> parameter allows
 *      to treat a string as an integer written to the base 256. Since
 *      <nValue> is limited to a signed long, only substrings 4 characters
 *      long can be affected by one ADDASCII() call.
 *      If the length of <[@]cString> is smaller than <nPosition>, the
 *      string remains unchanged. The same happens, if uninterpretable
 *      parameters are passed to this function.
 *  $EXAMPLES$
 *      // Add 32 to the ASCII value of the character at the last position
 *      // in the string
 *      
 *      ? addascii ("SmitH", 32)  --> "Smith"
 *  $TESTS$
 *      addascii ("0000", 1, 1) == "1000"
 *      addascii ("0000", 1) == "0001" 
 *      addascii ("AAAA", -255, 1) == "BAAA"
 *      addascii ("AAAA", -255) == "AAAB"
 *      addascii ("AAAA", 1, 2, .T.) == "ABAA"
 *      addascii ("AAAA", 257, 2, .T.) == "BBAA"
 *      addascii ("AAAA", 257, 2, .F.) == "ABAA"
 *      addascii ("AAAA", 258,, .T.) == "AABC"
 *      addascii ("ABBA", -257, 3, .T.) == "AAAA"
 *  $STATUS$
 *      Ready
 *  $COMPLIANCE$
 *      ADDASCII() is compatible with CT3's ADDASCII().
 *      A new, 4th, parameter has been added who defaults to the original
 *      behaviour if omitted.
 *  $PLATFORMS$
 *      All
 *  $FILES$
 *      Source is addascii.c, library is ct3.
 *  $SEEALSO$
 *      CSETREF() 
 *  $END$
 */

HB_FUNC( ADDASCII )
{
   int iNoRet;

   /* suppressing return value ? */
   iNoRet = ct_getref() && ISBYREF( 1 );

   if( ISCHAR( 1 ) )
   {
      char *pcSource = hb_parc( 1 );
      size_t sLen = hb_parclen( 1 );
      char *pcResult;
      size_t sPos;
      LONG lValue;
      int iCarryOver;

      if( ISNUM( 3 ) )
         sPos = hb_parnl( 3 );
      else
         sPos = sLen;

      if( sPos > sLen || !ISNUM( 2 ) || sLen == 0 )
      {
         int iArgErrorMode = ct_getargerrormode();

         if( iArgErrorMode != CT_ARGERR_IGNORE )
         {
            ct_error( ( USHORT ) iArgErrorMode, EG_ARG, CT_ERROR_ADDASCII, NULL,
                      "ADDASCII", 0, EF_CANDEFAULT, HB_ERR_ARGS_BASEPARAMS );
         }
         /* return string unchanged */
         if( iNoRet )
            hb_retl( 0 );
         else
            hb_retclen( pcSource, sLen );
         return;
      }

      pcResult = ( char * ) hb_xgrab( sLen + 1 );
      hb_xmemcpy( pcResult, pcSource, sLen );

      lValue = hb_parnl( 2 );
      if( ISLOG( 4 ) )
         iCarryOver = hb_parl( 4 );
      else
         iCarryOver = 0;

      if( iCarryOver )
      {
         size_t sCurrent;
         LONG lResult;

         for( sCurrent = sPos; sCurrent > 0 && lValue != 0; sCurrent-- )
         {
            lResult = ( LONG ) pcSource[sCurrent - 1] + ( lValue % 256 );

            lValue /= 256;
            if( lResult > 255 )
               lValue++;
            else if( lResult < 0 )
               lValue--;

            pcResult[sCurrent - 1] = ( char ) ( lResult % 256 );
         }
      }
      else
      {
         pcResult[sPos - 1] = ( char ) ( ( ( LONG ) pcResult[sPos - 1] + lValue ) % 256 );
      }

      if( ISBYREF( 1 ) )
         hb_storclen( pcResult, sLen, 1 );

      if( iNoRet )
      {
         hb_retl( 0 );
         hb_xfree( pcResult );
      }
      else
         hb_retclen_buffer( pcResult, sLen );
   }
   else
   {
      PHB_ITEM pSubst = NULL;
      int iArgErrorMode = ct_getargerrormode();

      if( iArgErrorMode != CT_ARGERR_IGNORE )
      {
         pSubst = ct_error_subst( ( USHORT ) iArgErrorMode, EG_ARG, CT_ERROR_ADDASCII,
                                  NULL, "ADDASCII", 0, EF_CANSUBSTITUTE, HB_ERR_ARGS_BASEPARAMS );
      }

      if( pSubst != NULL )
         hb_itemReturnRelease( pSubst );
      else if( iNoRet )
         hb_retl( 0 );
      else
         hb_retc( NULL );
   }
}
