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一个关于Delphi CRC算法的源码

  •   时间:2019-07-10
  • 概述:CRC 算法

这是一个关于CRC算法的源码,里面有注释,演示CRC在Delphi中的用法,代码较老仅供参考:

unit Unit1;
//www.srcfans.com
interface
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, Buttons;
type
  TForm1 = class(TForm)
    Button1: TButton;
    Edit1: TEdit;
    SpeedButton1: TSpeedButton;
    OpenDialog1: TOpenDialog;
    procedure Button1Click(Sender: TObject);
    procedure SpeedButton1Click(Sender: TObject);
  private
  procedure CalcCRC32(FileName: String; var CRC32: dword);
    { Private declarations }
  public
    { Public declarations }
  end;
var
  Form1: TForm1;
  Fname : String;
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);
procedure TForm1.Button1Click(Sender: TObject);
var
  crc :dword;
begin
  if Fname<>'' then
  begin
    CalcCRC32(Fname,crc);
    if crc<>0 then
    ShowMessage(IntToHex(crc,6));
  end
  else
    showmessage('请选择指定文件的路径。');
end;
procedure TForm1.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.SpeedButton1Click(Sender: TObject);
begin
  if OpenDialog1.Execute then
  begin
    Edit1.Text := OpenDialog1.FileName;
    Fname := Trim(Edit1.Text);
  end
  else
  begin
    Edit1.Text := '';
    Fname := '';
  end;
end;
{
原理:
CRC就是简单的用一个固定的数K去XOR待检的串A,得出的余数R附加在这个A上给传输出去。在接收端,用同样的这个数再去XOR。由于A XOR K=R,而B=A+R,如果传输过程没有错出错,则B XOR K=(A+R) XOR K=R XOR k=0,校验成功。(XOR是按位运算的)
定义:
在远距离数据通信中,为确保高效而无差错地传送数据,必须对数据进行校验,即差错控制。循环冗余校验CRC是对一个传送数据块进行校验,是一种高效的差错控制方法。
}
end.

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