This is a modified variant of the one written by Arp Dev / Foolish Corp. [article ID 1069]. It looks a little easier. I made it because Arp Dev's version didn't work with my progs (I/O Errors).

implementation

{$R *.DFM}

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 Buffer = Array[1..65521] of byte;
{largest buffer that can be allocated on heap }

procedure CalcCRC32(FileName: String; var CRC32: dword);
var F: file;
    BytesRead: dword;
    Buffer: Array[1..65521] ofBbyte;
    i: Word;
begin
     FileMode := 0;
     CRC32 := $ffffffff;
     {$I-}
     AssignFile(F, FileName); Reset(F, 1);
     if IOResult = 0 then begin
        repeat
           BlockRead(F, Buffer, SizeOf(Buffer), BytesRead);
           for i := 1 to BytesRead do
              CRC32 := (CRC32 shr 8) xor Table[Buffer[i] xor (CRC32 and $000000FF)];
        until BytesRead = 0;
     end;
     CloseFile(F);
     {$I+}
     CRC32 := not CRC32;
end;