Delphi Forum

Mesaj gönderen **şimal** » 05 Nis 2004 06:16

16 bit CRC ile ilgili bilgisi olan varmı?
Elektronik devre şeması var elimde ama çözemedim:(
Bunu delphi ile nasıl yapabilirim?

Mesaj gönderen **mege** » 06 Nis 2004 09:01

http://www.efg2.com/Lab/Mathematics/CRC.htm

Esasında çok iyi bir yöntem kullanmamış ama buradan yola çıkabilirsin.
Arkadaş VCL halinde bile hazırlamış bunu

)

Kod: Tümünü seç

 Given the above  lookup table, the code for computing a CRC-16 is as follows (see initialization/finalization below):
PROCEDURE CalcCRC16 (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 Table[ q^ XOR Lo(CRCvalue) ];
    INC(q)
  END
END {CalcCRC16};

Başka bir yöntem FASTCRC
http://atlas.csd.net/~cgadd/knowbase/CRC0015.HTM

Kod: Tümünü seç

Contributor: DON PAULSEN              


{
RE:     SWAG submission
        This 16-bit CRC function is compatible with those used in Chuck
        Forsberg's X-modem protocol.  It's very fast, because I unrolled
        the "for (i = 0; i < 8; ++i)" loop.  If a 32-bit CRC is not
        necessary, this is a great alternative because of its speed and
        small size.



{==============================================================}
FUNCTION Crc16 (var buffer; size, seed: word): word; assembler;

{ Set size parameter to 0 to process 64K.  If processing only one buffer, set
  seed parameter to 0 -- otherwise set to result from previous calculation.
  C code translated by Don Paulsen. }

(* This routine is a translation of the following C code by Chuck Forsberg.
   The added "seed" parameter allows for finding the CRC value of data spanning
   multiple buffers.  The innermost loop has been unrolled at a cost of 32
   bytes in code, but the speed increase is nearly two-fold.

     int    Crc16 (ptr, count)
     char   *ptr;
     int    count;

     {   int crc, i;

         crc = 0;
         while (--count >= 0) {
            crc = crc ^ (int)*ptr++ << 8;
            for (i = 0; i < 8; ++i)
                if (crc & 0x8000)
                    crc = crc << 1 ^ 0x1021;
                else
                    crc = crc << 1;
          }
         return (crc & 0xFFFF);
     }
*)

ASM
    les     di, buffer
    mov     dx, size
    mov     ax, seed
    mov     si, 1021h
@next:
    xor     bl, bl
    mov     bh, es:[di]
    xor     ax, bx

    shl  ax, 1;    jnc  @noXor1;    xor  ax, si
@noXor1:
    shl  ax, 1;    jnc  @noXor2;    xor  ax, si
@noXor2:
    shl  ax, 1;    jnc  @noXor3;    xor  ax, si
@noXor3:
    shl  ax, 1;    jnc  @noXor4;    xor  ax, si
@noXor4:
    shl  ax, 1;    jnc  @noXor5;    xor  ax, si
@noXor5:
    shl  ax, 1;    jnc  @noXor6;    xor  ax, si
@noXor6:
    shl  ax, 1;    jnc  @noXor7;    xor  ax, si
@noXor7:
    shl  ax, 1;    jnc  @noXor8;    xor  ax, si
@noXor8:

    inc     di
    dec     dx
    jnz     @next
END;

Hata sezme ile ilgili (Hamming Distance) arkadaşımın okul notları var. istenirse admine gönderebilirim. faydalı bir eser.

mbt · Mesaj gönderen **mbt** » 06 Nis 2004 12:06

Bu konu hakkında pascal kodu olan bir örnek program var. Turbo Pascal 7.0 ile uyumlu ama delphi'ye de sizler uyarlayabilirsiniz. Belki yardımı olur kanısındayım.

Kod: Tümünü seç

UNIT CRC;

{CRC calculates a cyclic redundancy code (CRC), known as CRC-16, using
  a byte-wise algorithm.

  (C) Copyright 1989, Earl F. Glynn, Overland Park, KS.  Compuserve 73257,3527.
  All Rights Reserved.  This Turbo Pascal 5.5 UNIT may be freely distributed
  for non-commercial use.

  This UNIT was derived from the CRCT FORTRAN 77 program given in
  "Byte-wise CRC Calculations" by Aram Perez in IEEE Micro, June 1983,
  pp. 40-50.  The constants here are for the CRC-16 generator polynomial,
  X^16 + X^15 + X^2 + 1.  While the constants are specific to the
  CRC-16 polynomial, the algorithm is general and will calculate the
  CRC for whatever set of constants is present.

  This CRC algorithm emphasizes speed at the expense of the 512-byte
  lookup table.}

INTERFACE

  PROCEDURE CalcCRC (p:  pointer; nbyte:  WORD; VAR CRCvalue:  WORD);
  PROCEDURE CalcFileCRC (FromName:  STRING; VAR CRCvalue:  WORD;
              VAR IOBuffer:  pointer;  BufferSize:  WORD; VAR error:  WORD);

IMPLEMENTATION

  CONST
    table:  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);

  TYPE
    buffer = ARRAY[1..65521] OF BYTE;  {largest buffer that can be}
                                       {allocated on heap         }
  VAR
    i:  WORD;
    q:  ^buffer;

  PROCEDURE CalcCRC (p:  pointer; nbyte:  WORD; VAR CRCvalue:  WORD);
   {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
      CRCvalue := Hi(CRCvalue)  XOR  Table[ q^[i] XOR Lo(CRCvalue) ]
  END {CalcCRC};

  PROCEDURE CalcFileCRC (FromName:  STRING; VAR CRCvalue:  WORD;
              VAR IOBuffer:  pointer;  BufferSize:  WORD; VAR error:  WORD);
    VAR
      BytesRead:  WORD;
      FromFile :  FILE;
      i        :  WORD;
  BEGIN
    FileMode := 0;  {Turbo default is 2 for R/W; 0 is for R/O}
    CRCValue := 0;
    ASSIGN (FromFile,FromName);
    {$I-} RESET (FromFile,1); {$I+}
    error := IOResult;
    IF   error = 0
    THEN BEGIN
      REPEAT
        BlockRead (FromFile,IOBuffer^,BufferSize,BytesRead);
        CalcCRC (IOBuffer,BytesRead,CRCvalue)
      UNTIL BytesRead = 0;
      CLOSE (FromFile)
    END;
  END; {CalcFileCRC};

END. {CRC}.

Mesaj gönderen **şimal** » 06 Nis 2004 12:17

çok teşekkürler
mege beyi in verdiği linki detaylıca inceledim
http://www.efg2.com/Lab/Mathematics/CRC.htm

ikinci gelen örnek kodun bir benzeri burada var...

sıradaki sorum 32 bit CRC idi onada cvp veren bir link...
örnek proje mevcut çok yardımcı oldu çççççooooookkkkk
tşkler sağlıcakla kalın

Mesaj gönderen **şimal** » 06 Nis 2004 05:59

http://www.ibrtses.com/delphi/dcrc.html

CRC-16 yı çok şık biçimde anlatıyor:) vede çok kolay bu yöntemi çok sevdim...

[quote]"Hata sezme ile ilgili (Hamming Distance) arkadaşımın okul notları var. istenirse admine gönderebilirim. faydalı bir eser."[/quote]
demişsiniz mege bey

mümkünse size ve adminimize zahmet olmazsa alabilir miyim?
(hangi okulun hangi derse ait ne notu bu?)