CRC8算法DELPHI源码

　　最近做个程序需要用到CRC8校验，网上找了一堆资料都看得头晕脑胀的，最终还是搞不懂它的算法，惭愧。最后找了个C源码请高手翻译成DELPHI的才解决问题。在这感谢　老鸨。。他写的DELPHI程序如下：

unit Crc8;

interface

Uses
  Classes, Windows;

Function Crc_8n(p : array of BYTE; len : BYTE) : Byte;

implementation

Function Crc_8n(p : array of BYTE; len : BYTE) : Byte;
Var
  j, cbit, aout, crc, crc_a, crc_b : Byte;
  i : integer;
begin
  crc := 0;
  i := 0;

  // 取移位的位
  repeat
   crc_a := p[i];
    inc(i);
   j := 8;
   cbit := 1;
    repeat
      crc_b := crc_a;
     crc_b := crc_b xor crc; // ?????
     aout := crc_b and cbit;
     if aout<>0 then begin
        crc := crc xor $18; // ?????
        crc := crc shr 1;
        crc := crc or $80;
     end else begin
       crc := crc shr 1;
     end;
     crc_a := crc_a shr 1;
      dec(j);
    until j = 0;
    dec(len);
  until len = 0;

  result := crc;
end;

end.

=================================

unit main;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls,
  Crc8;

type
  TForm1 = class(TForm)
    Edit1: TEdit;
    Memo1: TMemo;
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

const MinBase = 2;
      MaxBase = 36;
     
function StrToNum (const s: string; base: Integer;
                   neg: Boolean; max: Integer): Integer;
// s = 要转换的字符串
// base = 进制数
// neg = 是否为负数

// max = 要转换的最大数//
// 用法:
// i:= StrToNum (''''''''00101101'''''''', 2, false, MaxInt);
// i:= StrToNum (''''''''002D'''''''', 16, false, MaxInt);
// i:= StrToNum (''''''''-45'''''''', 10, true, MaxInt);
// i:= StrToNum (''''''''ZZ'''''''', 36, true, MaxInt);
//
var negate, done: Boolean;
    i, len, digit, mmb: Integer;
    c: Char;
    mdb, res: Integer;
begin
res:= 0;  i:= 1;  digit:= 0;
if (base >= MinBase) and (base <= MaxBase) then begin
  mmb:= max mod base;
  mdb:= max div base;
  len:= Length (s);
  negate:= False;
  while (i <= len) and (s[i] = '''' '''') do Inc (i);
  if neg then begin
   case s[i] of
    ''''+'''': Inc (i);
    ''''-'''': begin  Inc (i);  negate:= TRUE; end;
   end; (* CASE *)
  end; (* IF neg *)
  done:= len > i;
  while (i <= len) and done do begin
   c:= Upcase (s[i]);
   case c of
    ''''0''''..''''9'''': digit:= ORD(c) - 48;
    ''''A''''..''''Z'''': digit:= ORD(c) - 55;
    else      done:= FALSE
   end; (* CASE *)
   done:= done and (digit < base);
   if done then begin
    done:= (res < mdb) or ((res = mdb) and (digit <= mmb));
    IF done then begin
     res:= res * base + digit;
     Inc (i);
    end; (* IF done *)
   end; (* IF done *)
  end; (* WHILE *)
  if negate then res:= - res;
end; (* IF done *)
Result:= res;
end;

procedure TForm1.Button1Click(Sender: TObject);
Var
  S : String;
  P : Array[0..255] of Byte;
  Len : Byte;
  R : Byte;
  I : Integer;
begin
  S := Edit1.Text;

  if length(s) mod 2 = 1 then s := s + ''''0'''';

  Memo1.Lines.Add(S + '''' :'''');
  for i:=1 to length(s) div 2 do begin
    p[i-1] := BYTE(StrToNum(copy(s, (i-1)*2+1, 2), 16, false, 500));
    Memo1.Lines.Add(IntToStr(I) + '''' --> '''' + IntToHex(p[i-1], 2));
  end;

  Len := length(s) div 2;

  R := Crc_8n(P, Len);
  Memo1.Lines.Add(''''Crc8 Result: '''' + IntToHex(R, 2));
end;

end.

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