/// unit obsahujuci funkcie na vypocitanie CRC32 pre polia a retazce
unit crc32;

interface

uses
  Windows, Messages, SysUtils, constants, tables;

PROCEDURE CalcCRC32 (p: pointer; ByteCount: DWORD; VAR CRCValue: DWORD);
function calculateCRC32(p: PChar; length: Integer; start: DWORD = $FFFFFFFF): DWORD;
function stringToCRC32(const S: xString; WS: TCharSet = nil; bCaseSensitive: Boolean = false): DWORD;

implementation

const
  table:  ARRAY[0..255] OF DWORD =
 ($00000000, $77073096, $EE0E612C, $990951BA,
  $076DC419, $706AF48F, $E963A535, $9E6495A3,
  $0EDB8832, $79DCB8A4, $E0D5E91E, $97D2D988,
  $09B64C2B, $7EB17CBD, $E7B82D07, $90BF1D91,
  $1DB71064, $6AB020F2, $F3B97148, $84BE41DE,
  $1ADAD47D, $6DDDE4EB, $F4D4B551, $83D385C7,
  $136C9856, $646BA8C0, $FD62F97A, $8A65C9EC,
  $14015C4F, $63066CD9, $FA0F3D63, $8D080DF5,
  $3B6E20C8, $4C69105E, $D56041E4, $A2677172,
  $3C03E4D1, $4B04D447, $D20D85FD, $A50AB56B,
  $35B5A8FA, $42B2986C, $DBBBC9D6, $ACBCF940,
  $32D86CE3, $45DF5C75, $DCD60DCF, $ABD13D59,
  $26D930AC, $51DE003A, $C8D75180, $BFD06116,
  $21B4F4B5, $56B3C423, $CFBA9599, $B8BDA50F,
  $2802B89E, $5F058808, $C60CD9B2, $B10BE924,
  $2F6F7C87, $58684C11, $C1611DAB, $B6662D3D,

  $76DC4190, $01DB7106, $98D220BC, $EFD5102A,
  $71B18589, $06B6B51F, $9FBFE4A5, $E8B8D433,
  $7807C9A2, $0F00F934, $9609A88E, $E10E9818,
  $7F6A0DBB, $086D3D2D, $91646C97, $E6635C01,
  $6B6B51F4, $1C6C6162, $856530D8, $F262004E,
  $6C0695ED, $1B01A57B, $8208F4C1, $F50FC457,
  $65B0D9C6, $12B7E950, $8BBEB8EA, $FCB9887C,
  $62DD1DDF, $15DA2D49, $8CD37CF3, $FBD44C65,
  $4DB26158, $3AB551CE, $A3BC0074, $D4BB30E2,
  $4ADFA541, $3DD895D7, $A4D1C46D, $D3D6F4FB,
  $4369E96A, $346ED9FC, $AD678846, $DA60B8D0,
  $44042D73, $33031DE5, $AA0A4C5F, $DD0D7CC9,
  $5005713C, $270241AA, $BE0B1010, $C90C2086,
  $5768B525, $206F85B3, $B966D409, $CE61E49F,
  $5EDEF90E, $29D9C998, $B0D09822, $C7D7A8B4,
  $59B33D17, $2EB40D81, $B7BD5C3B, $C0BA6CAD,

  $EDB88320, $9ABFB3B6, $03B6E20C, $74B1D29A,
  $EAD54739, $9DD277AF, $04DB2615, $73DC1683,
  $E3630B12, $94643B84, $0D6D6A3E, $7A6A5AA8,
  $E40ECF0B, $9309FF9D, $0A00AE27, $7D079EB1,
  $F00F9344, $8708A3D2, $1E01F268, $6906C2FE,
  $F762575D, $806567CB, $196C3671, $6E6B06E7,
  $FED41B76, $89D32BE0, $10DA7A5A, $67DD4ACC,
  $F9B9DF6F, $8EBEEFF9, $17B7BE43, $60B08ED5,
  $D6D6A3E8, $A1D1937E, $38D8C2C4, $4FDFF252,
  $D1BB67F1, $A6BC5767, $3FB506DD, $48B2364B,
  $D80D2BDA, $AF0A1B4C, $36034AF6, $41047A60,
  $DF60EFC3, $A867DF55, $316E8EEF, $4669BE79,
  $CB61B38C, $BC66831A, $256FD2A0, $5268E236,
  $CC0C7795, $BB0B4703, $220216B9, $5505262F,
  $C5BA3BBE, $B2BD0B28, $2BB45A92, $5CB36A04,
  $C2D7FFA7, $B5D0CF31, $2CD99E8B, $5BDEAE1D,

  $9B64C2B0, $EC63F226, $756AA39C, $026D930A,
  $9C0906A9, $EB0E363F, $72076785, $05005713,
  $95BF4A82, $E2B87A14, $7BB12BAE, $0CB61B38,
  $92D28E9B, $E5D5BE0D, $7CDCEFB7, $0BDBDF21,
  $86D3D2D4, $F1D4E242, $68DDB3F8, $1FDA836E,
  $81BE16CD, $F6B9265B, $6FB077E1, $18B74777,
  $88085AE6, $FF0F6A70, $66063BCA, $11010B5C,
  $8F659EFF, $F862AE69, $616BFFD3, $166CCF45,
  $A00AE278, $D70DD2EE, $4E048354, $3903B3C2,
  $A7672661, $D06016F7, $4969474D, $3E6E77DB,
  $AED16A4A, $D9D65ADC, $40DF0B66, $37D83BF0,
  $A9BCAE53, $DEBB9EC5, $47B2CF7F, $30B5FFE9,
  $BDBDF21C, $CABAC28A, $53B39330, $24B4A3A6,
  $BAD03605, $CDD70693, $54DE5729, $23D967BF,
  $B3667A2E, $C4614AB8, $5D681B02, $2A6F2B94,
  $B40BBE37, $C30C8EA1, $5A05DF1B, $2D02EF8D);

/// procedura pocitajuca CRC32 pre pole zacinajuce v pamati na adrese p, dlhe bytecount bytov
/// v hodnote CRCValue vracia vypocitane CRC32
//nasledujuca procedura pocitajuca CRC32 je prebrata zo stranky Earl F. Glynna,
//webova adresa: http://www.efg2.com/Lab/Mathematics/CRC.htm
//***********************************************************
// Use CalcCRC32 as a procedure so CRCValue can be passed in but
// also returned. This allows multiple calls to CalcCRC32 for
// the "same" CRC-32 calculation.
PROCEDURE CalcCRC32 (p: pointer; ByteCount: DWORD; VAR CRCValue: DWORD);
  // The following is a little cryptic (but executes very quickly).
  // The algorithm is as follows:
  // 1. exclusive-or the input byte with the low-order byte of
  // the CRC register to get an INDEX
  // 2. shift the CRC register eight bits to the right
  // 3. exclusive-or the CRC register with the contents of Table[INDEX]
  // 4. repeat steps 1 through 3 for all bytes
VAR
    i:  DWORD;
    q: ^BYTE;
BEGIN
  q := p;
  FOR i := 0 TO ByteCount-1 DO
  BEGIN
    CRCvalue := (CRCvalue SHR 8) XOR
    Table[ q^ XOR (CRCvalue AND $000000FF) ];
    INC(q)
  END
END {CalcCRC32};
//***********************************************************

/// funkcia vracajuca CRC32 pre vstupny string na adrese p, dlzky length, s pripadnou vstupnou hodnotou start
function calculateCRC32(p: PChar; length: Integer; start: DWORD = $FFFFFFFF): DWORD;
var I: Integer;
begin
  result := start;
  for I := 0 to length-1 do
  begin
    result := (result shr 8) xor table[pbyte(p)^ xor (result and $000000ff)];
    inc(p);
  end;
end;

/// funkcia vracajuca CRC32 pre vstupny string, ak je WS <> nil, tak sa pred vypoctom odfiltruju WS znaky zo vstupneho stringu,
/// ak je vstupny parameter bCaseSensitive nastaveny na false, tak sa vstupny string pred vypoctom transformuje na cisto male pismena (lowercase)
function StringToCRC32(const S: xString; WS: TCharSet = nil; bCaseSensitive: Boolean = false): DWORD;
var i, j, len: integer;
    newS,newerS: xString;
begin
{  newS := S;

  i := 1;
  j := 1;
  len := Length(S);
  if WS <> nil then begin
    while i <= len do begin
      if not (WS.haschar(S[i])) then begin
        if bCaseSensitive then
          newS[j] := S[i]
        else
          newS[j] := AnsiLowerCase(S[i])[1];
        inc(j);
      end;
      inc(i);
    end;
    SetLength(newS,j-1);
  end
  else if not bCaseSensitive then begin
    while i <= len do begin
      newS[j] := AnsiLowerCase(S[i])[1];
      inc(j);
      inc(i);
    end;
    SetLength(newS,j-1);
  end;

  result := calculateCRC32(PChar(newS),Length(newS));
}
  if WS = nil then begin
    if not bCaseSensitive then begin  //!UNICODE!
      newS := AnsiLowerCase(S);
      result := calculateCRC32(PChar(newS),Length(newS));
    end
    else
      result := calculateCRC32(PChar(S),Length(S));
  end
  else begin
    if not bCaseSensitive then begin  //!UNICODE!
      newS := AnsiLowerCase(S);
    end
    else
      newS := S;

    i := 1;
    j := 1;
    len := Length(newS);
    SetLength(newerS,len);
    while i <= len do begin
      if not (WS.haschar(newS[i])) then begin
        newerS[j] := newS[i];
        inc(j);
      end;
      inc(i);
    end;
    SetLength(newerS,j-1);
(*
    if not bCaseSensitive then begin
      newS := AnsiLowerCase(newS);
      result := calculateCRC32(PChar(newS),Length(newS));
    end
    else
      result := calculateCRC32(PChar(newS),Length(newS));
*)
    result := calculateCRC32(PChar(newerS),Length(newerS));
  end;
end;

end.
