Streams vergleichen?

[Thebe]

Delphi-Quellcode:

const

        Table: array[0..255] of DWORD =
                ($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);

procedure CalcCRC32(p: Pointer; ByteCount: cardinal; var CRCValue: cardinal);
  // 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: cardinal;
        q: ^BYTE;
begin
        q := p;
        for i := 0 to ByteCount - 1 do
        begin
                CRCvalue := (CRCvalue shr 8) xor
                                Table[q^ xor (CRCvalue and $000000FF)];
                Inc(q)
        end;
end;

function StreamCRC32(s: TStream; len: cardinal): cardinal;
var
        p: Pointer;
begin
                result := $8F808F80;

                GetMem(p, len);

                s.Read(p^, len);

                CalcCRC32(p, len, result);

                FreeMem(p, len);
end;

Solche Fehlerkorrekturen wie "Stream auch groß genug?" "Stream nicht an Pos -1?" etc. hab ich hier nicht eingebaut, musst Du Dich drum kümmern. Auch das der Stream wieder "zurückgespult" wird, muss Du noch bedenken (Man glaubt gar nich wieviele Fehler durch so ein Schwachsinn entstehen können*g*). Ich schreibe erst vom Stream in einen Buffer und führe die CRC Routine mit dem Buffer aus, weil nicht alle Streams z.b. FileStream per Pointer erreichbar sind.

Die CalcCRC32 Prozedur samt Konstanten Tabelle hab ich vom swissdelphicenter.ch