Author: Arp Dev

How to get the CRC value

Answer:

1   implementation
2   const
3     Table: array[0..255] of LongInt = ($00000000, $77073096, $EE0E612C, $990951BA,
4       $076DC419, $706AF48F, $E963A535, $9E6495A3, $0EDB8832, $79DCB8A4, $E0D5E91E,
5       $97D2D988, $09B64C2B, $7EB17CBD, $E7B82D07, $90BF1D91, $1DB71064, $6AB020F2,
6       $F3B97148, $84BE41DE, $1ADAD47D, $6DDDE4EB, $F4D4B551, $83D385C7, $136C9856,
7       $646BA8C0, $FD62F97A, $8A65C9EC, $14015C4F, $63066CD9, $FA0F3D63, $8D080DF5,
8       $3B6E20C8, $4C69105E, $D56041E4, $A2677172, $3C03E4D1, $4B04D447, $D20D85FD,
9       $A50AB56B, $35B5A8FA, $42B2986C, $DBBBC9D6, $ACBCF940, $32D86CE3, $45DF5C75,
10      $DCD60DCF, $ABD13D59, $26D930AC, $51DE003A, $C8D75180, $BFD06116, $21B4F4B5,
11      $56B3C423, $CFBA9599, $B8BDA50F, $2802B89E, $5F058808, $C60CD9B2, $B10BE924,
12      $2F6F7C87, $58684C11, $C1611DAB, $B6662D3D, $76DC4190, $01DB7106, $98D220BC,
13      $EFD5102A, $71B18589, $06B6B51F, $9FBFE4A5, $E8B8D433, $7807C9A2, $0F00F934,
14      $9609A88E, $E10E9818, $7F6A0DBB, $086D3D2D, $91646C97, $E6635C01, $6B6B51F4,
15      $1C6C6162, $856530D8, $F262004E, $6C0695ED, $1B01A57B, $8208F4C1, $F50FC457,
16      $65B0D9C6, $12B7E950, $8BBEB8EA, $FCB9887C, $62DD1DDF, $15DA2D49, $8CD37CF3,
17      $FBD44C65, $4DB26158, $3AB551CE, $A3BC0074, $D4BB30E2, $4ADFA541, $3DD895D7,
18      $A4D1C46D, $D3D6F4FB, $4369E96A, $346ED9FC, $AD678846, $DA60B8D0, $44042D73,
19      $33031DE5, $AA0A4C5F, $DD0D7CC9, $5005713C, $270241AA, $BE0B1010, $C90C2086,
20      $5768B525, $206F85B3, $B966D409, $CE61E49F, $5EDEF90E, $29D9C998, $B0D09822,
21      $C7D7A8B4, $59B33D17, $2EB40D81, $B7BD5C3B, $C0BA6CAD, $EDB88320, $9ABFB3B6,
22      $03B6E20C, $74B1D29A, $EAD54739, $9DD277AF, $04DB2615, $73DC1683, $E3630B12,
23      $94643B84, $0D6D6A3E, $7A6A5AA8, $E40ECF0B, $9309FF9D, $0A00AE27, $7D079EB1,
24      $F00F9344, $8708A3D2, $1E01F268, $6906C2FE, $F762575D, $806567CB, $196C3671,
25      $6E6B06E7, $FED41B76, $89D32BE0, $10DA7A5A, $67DD4ACC, $F9B9DF6F, $8EBEEFF9,
26      $17B7BE43, $60B08ED5, $D6D6A3E8, $A1D1937E, $38D8C2C4, $4FDFF252, $D1BB67F1,
27      $A6BC5767, $3FB506DD, $48B2364B, $D80D2BDA, $AF0A1B4C, $36034AF6, $41047A60,
28      $DF60EFC3, $A867DF55, $316E8EEF, $4669BE79, $CB61B38C, $BC66831A, $256FD2A0,
29      $5268E236, $CC0C7795, $BB0B4703, $220216B9, $5505262F, $C5BA3BBE, $B2BD0B28,
30      $2BB45A92, $5CB36A04, $C2D7FFA7, $B5D0CF31, $2CD99E8B, $5BDEAE1D, $9B64C2B0,
31      $EC63F226, $756AA39C, $026D930A, $9C0906A9, $EB0E363F, $72076785, $05005713,
32      $95BF4A82, $E2B87A14, $7BB12BAE, $0CB61B38, $92D28E9B, $E5D5BE0D, $7CDCEFB7,
33      $0BDBDF21, $86D3D2D4, $F1D4E242, $68DDB3F8, $1FDA836E, $81BE16CD, $F6B9265B,
34      $6FB077E1, $18B74777, $88085AE6, $FF0F6A70, $66063BCA, $11010B5C, $8F659EFF,
35      $F862AE69, $616BFFD3, $166CCF45, $A00AE278, $D70DD2EE, $4E048354, $3903B3C2,
36      $A7672661, $D06016F7, $4969474D, $3E6E77DB, $AED16A4A, $D9D65ADC, $40DF0B66,
37      $37D83BF0, $A9BCAE53, $DEBB9EC5, $47B2CF7F, $30B5FFE9, $BDBDF21C, $CABAC28A,
38      $53B39330, $24B4A3A6, $BAD03605, $CDD70693, $54DE5729, $23D967BF, $B3667A2E,
39      $C4614AB8, $5D681B02, $2A6F2B94, $B40BBE37, $C30C8EA1, $5A05DF1B, $2D02EF8D);
40  
41  type
42    buffer = array[1..65521] of byte; {largest buffer that can be
43    allocated on heap }
44  var
45    i: WORD;
46    q: ^buffer;
47  
48  procedure CalcCRC32(p: pointer; nbyte: Word; var CRCvalue: LongInt);
49  {The following is a little cryptic (but executes very quickly). The algorithm is as 
50  follows:
51  1. exclusive-or the input byte with the low-order portion of the CRC register to 
52  get an INDEX
53  2. shift the CRC register eight bits to the right
54  3. exclusive-or the CRC register with the contents of Table[INDEX]
55  4. repeat steps 1 through 3 for all bytes}
56  
57  var
58    i: Word;
59  begin
60    q := p;
61    for i := 1 to nBYTE do
62      CRCvalue := (CRCvalue shr 8) xor
63        Table[q^[i] xor (CRCvalue and $000000FF)]
64  end {CalcCRC32};
65  
66  procedure CalcFileCRC32(FromName: string; var CRCvalue: LongInt; var IOBuffer:
67    pointer; BufferSize: Word; var TotalBytes: LongInt; var error: WORD);
68  var
69    BytesRead: integer;
70    FromFile: file;
71  
72  begin
73    FileMode := 0; {Turbo default is 2 for R/W; 0 is for R/O}
74    CRCValue := $FFFFFFFF;
75    Assign(FromFile, FromName);
76  {$I-}Reset(FromFile, 1);
77  {$I+}Error := IOResult;
78    if error = 0 then
79    begin
80      TotalBytes := 0;
81      repeat BlockRead(FromFile, IOBuffer^, BufferSize, BytesRead);
82        CalcCRC32(IOBuffer, BytesRead, CRCvalue);
83        Inc(TotalBytes,
84          BytesRead)
85      until BytesRead = 0;
86      Close(FromFile)
87    end;
88    CRCvalue := not CRCvalue
89  end {CalcFileCRC32};