Checksum - calcul du crc-16 ou 32

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Description

Un algo pour calculer le CRC-16 ou 32 (checksum) pour une chaîne de caractères ou une suite d'octets en général. J'ai repris l'algo à l'adresse cité plus bas et j'ai tout encapsulé dans une classe avec quelques fonctions supplémentaires pour que ce soit plus simple à utiliser.

Pour l'utiliser, ajoutez le fichier .pas à votre projet, ajoutez la clause "uses CRCCalculator" et faites simplement :

CalcCRC := TCRCCalculator.Create();
monCRC16 := CalcCRC.StringCRC16('ma chaîne');
// ou bien:
monCRC32 := CalcCRC.StringCRC32('ma chaîne');

Source / Exemple : 


unit CRCCalculator;

interface

type TCRCCalculator = class(TObject)
  private
    TABLE16 : array[0..255] of word;
    TABLE32 : array[0..255] of LongWord;
  public
    constructor Create();
    PROCEDURE CRC16 (p: pByte; nbyte: WORD; VAR CRCvalue: WORD);
    PROCEDURE CRC32 (p: pointer; ByteCount: LongWord; VAR CRCValue: LongWord);
    function StringCRC16(const s : string ) : Word;
    function StringCRC32(const s : string ) : LongWord;
  end;

implementation

// Initialise les deux tables
constructor TCRCCalculator.Create();
    const _TABLE16 : array[0..255] of word =
     ($0000,$C0C1,$C181,$0140,$C301,$03C0,$0280,$C241,$C601,$06C0,$0780,
      $C741,$0500,$C5C1,$C481,$0440,$CC01,$0CC0,$0D80,$CD41,$0F00,$CFC1,
      $CE81,$0E40,$0A00,$CAC1,$CB81,$0B40,$C901,$09C0,$0880,$C841,$D801,
      $18C0,$1980,$D941,$1B00,$DBC1,$DA81,$1A40,$1E00,$DEC1,$DF81,$1F40,
      $DD01,$1DC0,$1C80,$DC41,$1400,$D4C1,$D581,$1540,$D701,$17C0,$1680,
      $D641,$D201,$12C0,$1380,$D341,$1100,$D1C1,$D081,$1040,$F001,$30C0,
      $3180,$F141,$3300,$F3C1,$F281,$3240,$3600,$F6C1,$F781,$3740,$F501,
      $35C0,$3480,$F441,$3C00,$FCC1,$FD81,$3D40,$FF01,$3FC0,$3E80,$FE41,
      $FA01,$3AC0,$3B80,$FB41,$3900,$F9C1,$F881,$3840,$2800,$E8C1,$E981,
      $2940,$EB01,$2BC0,$2A80,$EA41,$EE01,$2EC0,$2F80,$EF41,$2D00,$EDC1,
      $EC81,$2C40,$E401,$24C0,$2580,$E541,$2700,$E7C1,$E681,$2640,$2200,
      $E2C1,$E381,$2340,$E101,$21C0,$2080,$E041,$A001,$60C0,$6180,$A141,
      $6300,$A3C1,$A281,$6240,$6600,$A6C1,$A781,$6740,$A501,$65C0,$6480,
      $A441,$6C00,$ACC1,$AD81,$6D40,$AF01,$6FC0,$6E80,$AE41,$AA01,$6AC0,
      $6B80,$AB41,$6900,$A9C1,$A881,$6840,$7800,$B8C1,$B981,$7940,$BB01,
      $7BC0,$7A80,$BA41,$BE01,$7EC0,$7F80,$BF41,$7D00,$BDC1,$BC81,$7C40,
      $B401,$74C0,$7580,$B541,$7700,$B7C1,$B681,$7640,$7200,$B2C1,$B381,
      $7340,$B101,$71C0,$7080,$B041,$5000,$90C1,$9181,$5140,$9301,$53C0,
      $5280,$9241,$9601,$56C0,$5780,$9741,$5500,$95C1,$9481,$5440,$9C01,
      $5CC0,$5D80,$9D41,$5F00,$9FC1,$9E81,$5E40,$5A00,$9AC1,$9B81,$5B40,
      $9901,$59C0,$5880,$9841,$8801,$48C0,$4980,$8941,$4B00,$8BC1,$8A81,
      $4A40,$4E00,$8EC1,$8F81,$4F40,$8D01,$4DC0,$4C80,$8C41,$4400,$84C1,
      $8581,$4540,$8701,$47C0,$4680,$8641,$8201,$42C0,$4380,$8341,$4100,
      $81C1,$8081,$4040);

    const _TABLE32 : array[0..255] of LongWord =
     ($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);
var i : byte;
begin
  for i := 0 to 255 do begin
    TABLE16[i] := _TABLE16[i];
    TABLE32[i] := _TABLE32[i];
  end;
end;

PROCEDURE TCRCCalculator.CRC16 (p: pByte; nbyte: WORD; VAR CRCvalue: WORD);
VAR i: WORD;
    q: pByte;
  {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}
BEGIN
  q := p;
  FOR i := 1 TO nBYTE DO
  BEGIN
    CRCvalue := Hi(CRCvalue) XOR Table16[ q^ XOR Lo(CRCvalue) ];
    INC(q)
  END
END {CalcCRC16};

// also returned. This allows multiple calls to CalcCRC32 for
// the "same" CRC-32 calculation.
PROCEDURE TCRCCalculator.CRC32 (p: pointer; ByteCount: LongWord; VAR CRCValue: LongWord);
  // 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:  LongWord;
    q: ^BYTE;
BEGIN
  q := p;
  FOR i := 0 TO ByteCount-1 DO
  BEGIN
    CRCvalue := (CRCvalue SHR 8) XOR
    Table32[ q^ XOR (CRCvalue AND $000000FF) ];
    INC(q)
  END
END {CalcCRC32};

function TCRCCalculator.StringCRC16(const s : string ) : Word;
begin
  Result := 0;
  if length(s) > 0 then CRC16(@(s[1]), LENGTH(s), Result);
end;

function TCRCCalculator.StringCRC32(const s : string ) : LongWord;
begin
  Result := 0;
  if length(s) > 0 then CRC32(@(s[1]), LENGTH(s), Result);
end;

end.

Conclusion :


L'article de EFGS's Computer Lab sur le CRC:
http://www.efg2.com/Lab/Mathematics/CRC.htm
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