unit VDSP_CRC;

{
  VPatch 2 - CRC
  ==============

  (c) 2002-2003 Van de Sande Productions

  This unit can calculate the standard ZIP CRC32 for a filestream.

  What's new
  ----------
  2.0   20030811    Koen            Initial documentation
}

interface

uses Classes;

//var
//this is the CRC32 table
//  CRCTable: Array[0..255] of LongWord;
   {= (
//this table used to be inside the exe, but now it has been replaced by a calculation routine which saves 1 KB
$0,$77073096,$EE0E612C,$990951BA,$76DC419,
$706AF48F,$E963A535,$9E6495A3,$EDB8832,$79DCB8A4,
$E0D5E91E,$97D2D988,$9B64C2B,$7EB17CBD,$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,
$1DB7106,$98D220BC,$EFD5102A,$71B18589,$6B6B51F,
$9FBFE4A5,$E8B8D433,$7807C9A2,$F00F934,$9609A88E,
$E10E9818,$7F6A0DBB,$86D3D2D,$91646C97,$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,
$3B6E20C,$74B1D29A,$EAD54739,$9DD277AF,$4DB2615,
$73DC1683,$E3630B12,$94643B84,$D6D6A3E,$7A6A5AA8,
$E40ECF0B,$9309FF9D,$A00AE27,$7D079EB1,$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,
$26D930A,$9C0906A9,$EB0E363F,$72076785,$5005713,
$95BF4A82,$E2B87A14,$7BB12BAE,$CB61B38,$92D28E9B,
$E5D5BE0D,$7CDCEFB7,$BDBDF21,$86D3D2D4,$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}

function FileCRC(fs: TFileStream): Integer;

implementation

function FileCRC(fs: TFileStream): Integer;
const
  CRCBlock = 4096;
var
  CRCTable: Array[0..255] of LongWord;
  c: LongWord;  //!!! this must be an unsigned 32-bits var!
  Block: Array[0..CRCBlock-1] of Byte;
  i,j,bytesread: Integer;
begin
  //this used to be the InitCRC procedure
  For i:= 0 To 255 do begin
    c:= i;
    For j:= 0 To 7 do begin
      If (c And 1)=0 Then begin
        c:= (c div 2);
      end Else begin
        c:= (c div 2) Xor $EDB88320;
      End;
    end;
    CRCTable[i]:= c;
  end;
//  InitCRC procedure end;
  c:=$FFFFFFFF;
  fs.Seek(0,soFromBeginning);
  for i:=0 to (fs.Size div CRCBlock)+1 do begin
    bytesread:=fs.Read(Block,CRCBlock);
    for j:=0 to bytesread-1 do begin
      c:=CRCTable[(c and $FF) xor Block[j]] xor (((c and $FFFFFF00) div 256) and $FFFFFF);
    end;
  end;
  FileCRC:=c xor $FFFFFFFF;
end;

end.