CRC-CCITT (0xFFFF) function?

Question

Can someone help me with Delphi implementation of CRC-CCITT (0xFFFF)?

Already get the Java version, but confusing on how to port it to Delphi

public static int CRC16CCITT(byte[] bytes) {
    int crc = 0xFFFF;          // initial value
    int polynomial = 0x1021;   // 0001 0000 0010 0001  (0, 5, 12) 

    for (byte b : bytes) {
        for (int i = 0; i < 8; i++) {
            boolean bit = ((b   >> (7-i) & 1) == 1);
            boolean c15 = ((crc >> 15    & 1) == 1);
            crc <<= 1;
            if (c15 ^ bit) crc ^= polynomial;
         }
    }

    crc &= 0xffff;
    //System.out.println("CRC16-CCITT = " + Integer.toHexString(crc));
    return crc;
}

and for PHP implementation

<?php
function crc16($data)
 {
   $crc = 0xFFFF;
   for ($i = 0; $i < strlen($data); $i++)
   {
     $x = (($crc >> 8) ^ ord($data[$i])) & 0xFF;
     $x ^= $x >> 4;
     $crc = (($crc << 8) ^ ($x << 12) ^ ($x << 5) ^ $x) & 0xFFFF;
   }
   return $crc;
 }

score 12 · Answer 1 · edited May 23 '17 at 10:27

0xFFFF translates to $FFFF
& translates to and
^ translates to xor
<< translates to shl
>> translates to shr
x ^= y translates to x := x xor y, similar for &=, <<=, etc.

These operators generally have higher precedence in Delphi so they usually need to have their arguments parenthesized.

I'm quite sure that there are plenty of other implementations of CRC16 etc. for Delphi, see e.g. Improve speed on Crc16 calculation

Remy Lebeau · Answer 2 · 2019-07-18T09:34:39.627

9

function CRC16CCITT(bytes: TBytes): Word;
const
  polynomial = $1021;   // 0001 0000 0010 0001  (0, 5, 12)
var
  crc: Word;
  I, J: Integer;
  b: Byte;
  bit, c15: Boolean;
begin
  crc := $FFFF; // initial value
  for I := 0 to High(bytes) do
  begin
    b := bytes[I];
    for J := 0 to 7 do
    begin
      bit := (((b shr (7-J)) and 1) = 1);
      c15 := (((crc shr 15) and 1) = 1);
      crc := crc shl 1;
      if ((c15 xor bit) <> 0) then crc := crc xor polynomial;
    end;
  end;
  Result := crc and $ffff;
end;

edited Jul 18 '19 at 09:34

answered Feb 28 '11 at 21:40

Remy Lebeau

555,201
31
458
770

your code didn't work but thanks (something with operand): bit := (((b shr (7-I)) and 1) = 1); c15 := (((crc shr 15) and 1) = 1); – Dels Mar 02 '11 at 09:29
@peimanF is that a question or a statement? What is the actual problem? This code is a direct translation of the OP's Java code. The result should be the same. – Remy Lebeau Jul 18 '19 at 09:36

score 5 · Answer 3 · answered Feb 28 '11 at 09:50

5

You can find one in Delphi Encryption Compendium (DEC) component.

5 Checksums (CRC32, CRC16-CCITT, CRC16-Standard ...)

http://blog.digivendo.com/2008/11/delphi-encryption-compendium-dec-52-for-d2009-released/

answered Feb 28 '11 at 09:50

TridenT

4,879
1
32
56

Code fails indeed on Delphi XE7 – Gabriel Aug 03 '17 at 15:05

score 4 · Accepted Answer · answered Mar 02 '11 at 09:31

i found some code that works:

function crc16(Buffer:String;Polynom,Initial:Cardinal):Cardinal;
var
  i,j: Integer;
begin
Result:=Initial;
for i:=1 to Length(Buffer) do begin
  Result:=Result xor (ord(buffer[i]) shl 8);
  for j:=0 to 7 do begin
    if (Result and $8000)<>0 then Result:=(Result shl 1) xor Polynom
    else Result:=Result shl 1;
    end;
  end;
Result:=Result and $ffff;
end;

source : http://www.miscel.dk/MiscEl/CRCcalculations.html

score 1 · Answer 5 · answered Nov 01 '16 at 14:40

unit CRC16CCITT;

interface

  function ComputeCRC16CCITT(crc: word; const data: PByte; len:integer) : word;

implementation

const
  crc16_table: array [0..$FF] of word = (0,4489,8978,12955,17956,22445,25910,29887,35912,40385,44890,48851,51820,56293,59774,
    63735,4225,264,13203,8730,22181,18220,30135,25662,40137,36160,49115,44626,56045,52068,63999,
    59510,8450,12427,528,5017,26406,30383,17460,21949,44362,48323,36440,40913,60270,64231,51324,
    55797,12675,8202,4753,792,30631,26158,21685,17724,48587,44098,40665,36688,64495,60006,55549,
    51572,16900,21389,24854,28831,1056,5545,10034,14011,52812,57285,60766,64727,34920,39393,43898,
    47859,21125,17164,29079,24606,5281,1320,14259,9786,57037,53060,64991,60502,39145,35168,48123,
    43634,25350,29327,16404,20893,9506,13483,1584,6073,61262,65223,52316,56789,43370,47331,35448,
    39921,29575,25102,20629,16668,13731,9258,5809,1848,65487,60998,56541,52564,47595,43106,39673,
    35696,33800,38273,42778,46739,49708,54181,57662,61623,2112,6601,11090,15067,20068,24557,28022,
    31999,38025,34048,47003,42514,53933,49956,61887,57398,6337,2376,15315,10842,24293,20332,32247,
    27774,42250,46211,34328,38801,58158,62119,49212,53685,10562,14539,2640,7129,28518,32495,19572,
    24061,46475,41986,38553,34576,62383,57894,53437,49460,14787,10314,6865,2904,32743,28270,23797,
    19836,50700,55173,58654,62615,32808,37281,41786,45747,19012,23501,26966,30943,3168,7657,12146,
    16123,54925,50948,62879,58390,37033,33056,46011,41522,23237,19276,31191,26718,7393,3432,16371,
    11898,59150,63111,50204,54677,41258,45219,33336,37809,27462,31439,18516,23005,11618,15595,3696,
    8185,63375,58886,54429,50452,45483,40994,37561,33584,31687,27214,22741,18780,15843,11370,7921,
    3960);

  function ComputeCRC16CCITT(crc: word; const data: PByte; len:integer) : word;
  var
    i : integer;
  begin
    for i := 0 to len-1 do  
      crc := (crc shr 8) xor crc16_table[(crc xor data[i]) and $ff];
    result := crc;
  end;

end.

CRC-CCITT (0xFFFF) function?

5 Answers5

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