crc32.pas

unit crc32;

interface

const
 CRC32INIT = $FFFFFFFF;
{----------------------------------------------------------------}
{    Buffer - ìàññèâ áàéòîâ, äëÿ êîòîðîãî ïîäñ÷èòûâàåòñÿ CRC     }
{    CRC    - íà÷àëüíîå çíà÷åíèå CRC                             }
{    Count  - äëèíà áóôåðà                                       }
{----------------------------------------------------------------}
function CalculateBufferCRC32( CRC   : Cardinal;
                               const Buffer;
                               Count : Cardinal ) : Cardinal;
register;
{----------------------------------------------------------------}
{  Ðàñ÷åò 32-áèòîâîé CRC, àëãîðèòì àíàëîãè÷åí ïðèìåíÿåìîìó â     }
{ àðõèâàòîðàõ ZIP, ARJ. Ïðè ýòîì íà÷àëüíîå çíà÷åíèå CRC äîëæíî   }
{ áûòü ðàâíî CRC32INIT, à ïîñëå îêîí÷àíèÿ ïîäñ÷åòà îêîí÷àòåëüíàÿ }
{ CRC âû÷èñëÿåòñÿ ïî ôîðìóëå :                                   }
{           CRC := CRC xor CRC32INIT;                            }
{ Hàïðèìåð :                                                     }
{  var                                                           }
{   Buffer : array[1..8192] of Char;                             }
{   CRC    : Cardinal;                                           }
{   Count  : Cardinal;                                           }
{  .......                                                       }
{   CRC := CRC32INIT;                                            }
{   repeat                                                       }
{    BlockRead(F, Buffer, SizeOf( Buffer ), Count);              }
{    CRC := CalculateBufferCRC32( CRC, Buffer, Count );          }
{   until Eof(F);                                                }
{   CRC := CRC xor CRC32INIT;                                    }
{  .......                                                       }
{----------------------------------------------------------------}
implementation

const
CRC32Table : array[0..255] of Cardinal = (
 $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 );

function CalculateBufferCRC32( CRC   : Cardinal;
                               const Buffer;
                               Count : Cardinal ) : Cardinal;
assembler;
asm
 PUSH ESI
 PUSH EDI
 MOV ESI, Buffer
// MOV ECX, Count       // uncomment these strings
// MOV EAX, CRC         // if not use REGISTER calling convention
 CLD
@@Loop:
  MOV EDI, EAX                       // copy CRC into DI
  LODSB                              // load next byte into AL
  XOR EDI, EAX                       // put array index into DL
  SHR EAX, 8                         // shift CRC one byte right
  SHL DI, 2                          // correct DI
  XOR EAX, DWORD PTR CRC32Table[EDI] // calculate next CRC value
 LOOP @@Loop
 POP EDI
 POP ESI
end;

end.