Checksum Least significant byte of the sum of the other characters in
in hexadecimal characters (two characters, Start and Stop not
included in the sum)

13 03 30 33 1A

13 0C 30 43 1A

13 01 52 30 33 35 45 42 1A

the sum of the other characters in hexadecimal characters

two characters

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

unit uCRC32;

interface

uses Windows, Classes;

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
//----------------------------------crc32----------------------------------
 TInteger8 = Int64;

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: TInteger8; var error: Word);

implementation

 // 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
 Result := False;
 // 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 //ShowMessage('CRC32 Table CRC32 is ' +
     //IntToHex(Crc32Table, 8) +
     //', expecting $6FCF9E13')
 else
 begin
   CRC32 := $FFFFFFFF; // To match PKZIP
   if Length(s) > 0 then
   begin
     try
       CalcCRC32(Addr(s[1]), Length(s), CRC32);
       Result := True;
     except

     end;
   end;
   CRC32 := not CRC32; // To match PKZIP
 end;
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;

end.

function GetCheckSum(FileName : string) : DWORD;
var
 F : File of DWORD;
 P : Pointer;
 Fsize : DWORD;
 Buffer : Array [0..500] of DWORD;
begin  
 FileMode := 0;  
 AssignFile(F,FileName);  
 Reset(F);  
 Seek(F,FileSize(F) div 2);  
 Fsize := FileSize(F) -1 -FilePos(F);  
 if Fsize > 500 then
   Fsize := 500;

 BlockRead(F, Buffer, Fsize);
 Close (F);
 P := @Buffer;

 asm
   xor eax, eax
   xor ecx, ecx
   mov edi , p
   @again:
     add eax, [edi + 4*ecx]
     inc ecx
     cmp ecx, fsize
   jl @again
   mov @result, eax
 end;
end;