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 }

function CRC32(const Data; Size, CRC: LongWord): LongWord;

asm

         PUSH    EBX

         MOV     EBX, EAX //EBX := @Data

         MOV     EAX, ECX //EAX := CRC

         PUSH    ESI

         TEST    EDX, EDX //if Size=0 then exit

         JE      @@exit

 @@loop: MOVZX   ESI, BYTE PTR [EBX]

         MOVZX   ECX, AL

         XOR     ECX, ESI

         SHR     EAX, 8

         XOR     EAX, DWORD PTR [CRC32Table + ECX*4]

         INC     EBX

         DEC     EDX

         JNE     @@loop

 @@exit: POP     ESI

         POP     EBX

end;

procedure CalcCRC32(FileName: string; var CRC32: DWORD);

var  

 F: file;

 BytesRead: DWORD;

 Buffer: array[1..65521] of Byte;

 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;

procedure TForm1.Button1Click(Sender: TObject);

var

 crc: DWORD;

begin

 CalcCRC32('d:\test.txt', crc);

 if crc <> 0 then

   ShowMessage(IntToHex(crc, 6));

end;