unit Crc32Hash;
{$mode objfpc}{$H+}

interface 
uses 
  Classes, SysUtils, Dialogs;

procedure CalcCRC32(p: Pointer; ByteCount: DWORD; var CRCValue: DWORD);
function CalcStringCRC32(s: string; out CRC32: DWORD): Boolean;
procedure CalcFileCRC32(FromName: string; var CRCvalue: DWORD; var TotalBytes: Int64; var error: Word);

implementation

// The constants here are for the CRC-32 generator
// polynomial, as defined in the Microsoft
// Systems Journal, March 1995, pp. 107 - 108
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);

type
TInteger8 = Int64;
 {
  //----------------------------------crc32----------------------------------
{$IFDEF VER130} // This is a bit awkward
  // 8-byte integer
  TInteger8 = Int64; // Delphi 5
{$ELSE}
{$IFDEF VER120}
  TInteger8 = Int64; // Delphi 4
{$ELSE}
  TInteger8 = COMP; // Delphi  2 or 3
{$ENDIF}
{$ENDIF}
}
  //----------------------------------crc32----------------------------------

    // 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};

function CalcStringCRC32(s: string; out CRC32: DWORD): Boolean;
var
  CRC32Table: DWORD;
begin
  // Verify the table used to compute the CRCs has not been modified.
  // Thanks to Gary Williams for this suggestion, Jan. 2003.
  CRC32Table := $FFFFFFFF;
  CalcCRC32(Addr(Table[0]), SizeOf(Table), CRC32Table);
  CRC32Table := not CRC32Table;

  if CRC32Table <> $6FCF9E13 then
    {$IFDEF ResBuilder}
    writeln('!!! CRC32 Table CRC32 is ' + IntToHex(Crc32Table, 8) + ', expecting $6FCF9E13')
    {$ELSE}
    ShowMessage('CRC32 Table CRC32 is ' + IntToHex(Crc32Table, 8) + ', expecting $6FCF9E13')
    {$ENDIF}
  else
  begin
    CRC32 := $FFFFFFFF; // To match PKZIP
    if Length(s) > 0 {// Avoid access violation in D4  } then
      CalcCRC32(Addr(s[1]), Length(s), CRC32);
    CRC32 := not CRC32; // To match PKZIP
    Result := True;
  end;


  //ShowMessage('Get CRC is = ' +  IntToStr(CRC32));
end;

procedure CalcFileCRC32(FromName: string; var CRCvalue: DWORD;
  var TotalBytes: TInteger8;
  var error: Word);
var
  Stream: TMemoryStream;
begin
  error := 0;
  CRCValue := $FFFFFFFF;
  Stream := TMemoryStream.Create;
  try
    try
      Stream.LoadFromFile(FromName);
      if Stream.Size > 0 then
        CalcCRC32(Stream.Memory, Stream.Size, CRCvalue)
    except
      on E: EReadError do
        error := 1
    end;
    CRCvalue := not CRCvalue
  finally
    Stream.Free
  end;
end;

{
procedure TForm1.Button1Click(Sender: TObject);
var
  s: string;
  CRC32: DWORD;
begin
  s := 'Test String';
  if CalcStringCRC32(s, CRC32) then
    ShowMessage(IntToStr(crc32));
end;
}

end.