CRC32生成码表方法实现

核心提示： Table:Array[0..255] of DWord;PRocedure MakeTable();var i,j,Crc:integer;begin for i:=0 to 255 do begin Crc:=i; for j:=0 to 7 do begin if (Crc and 1)<

  Table:Array[0..255] of DWord;

PRocedure MakeTable();
var
  i,j,Crc:integer;
begin
  for i:=0 to 255 do
　  begin
　　  Crc:=i;
　　  for j:=0 to 7 do
　　　  begin
　　　　  if (Crc and 1)<>0 then
　　　　　  Crc:=(Crc shr 1) xor $EDB88320
　　　　  else
　　　　　  Crc:=Crc shr 1;
　　　  end;
　　  Table[i]:=Crc;
　  end;
end;

procedure GetCRC32File(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;
　 
function GetCrc32Str(s: string; Seed: LongInt):string;
var
  Count: Integer;
  CrcVal: LongInt;
begin
  CrcVal := Seed;
  for Count := 1 to Length(s) do
　  CrcVal := Table[Byte(CrcVal xor DWORD(Ord(s[Count])))] xor ((CrcVal shr 8) and $00FFFFFF);
  Result := IntToHex(not(CrcVal), 8);
end;

调用：
procedure TForm1.Button1Click(Sender: TObject);
begin
  MakeTable();
  Edit1.Text:=GetCrc32Str('11111111',8);//这里取指定字符串的CRC32校验值;
end;

procedure TForm1.Button2Click(Sender: TObject);
var
  FileStr:String;
  crc: DWORD; 
begin
  MakeTable();
  FileStr:=application.ExeName;//这里取指定的文件的crc32校验值;
  GetCRC32File(FileStr,crc);
  if crc<>0 then
　  Edit2.Text:=PChar(IntToHex(crc,6));
end;