Mega Code Archive
How to get a CRC 32 of a file
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Title: How to get a CRC-32 of a file.
Unit:
CODE
{$R- $Q- $O+}
Unit d3_crc32;
{ original credits below. CRC32Update added by Glenn9999@tek-tips.com
Modified from a version posted on the Pascal echo by Floor
A.C. Naaijkens (note introduction of a Constant and a
Function and making the Array a Constant outside of
crc32() which should improve speed a lot; further
references made to a C version in a File of Snippets from the
(112 min left), (H)elp, More? C Echo marked as "Copyright (C) 1986 Gary S. Brown" (mostly to
compare the large Arrays, which proved to be identical), and to
"File verification using CRC" by Mark R. Nelson in Dr. Dobbs'
Journal, May 1992. The latter provided the final piece of
crucial information. Use: 1) Create a LongInt Variable For the
CRC value; 2) Initialize this With CRCSeed; 3) Build the
CRC Byte-by-Byte With CRC32(); 4) Finish With CRCend()
(this was the part I found in Nelson). The result is a CRC
value identical to that calculated by PKZip and ARJ.
}
Interface
uses windows;
Const
CRCSeed = $ffffffff;
CRC32tab : 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, $2d02ef8d );
function crc32_update(inbuffer: pointer; buffersize, crc: DWord): DWord;
Function CRCend( crc : DWord ): DWord;
Implementation
function crc32_update(inbuffer: pointer; buffersize, crc: DWord): DWord;
// crc-32. Processes 4 bytes at a time.
type
PDWord = ^DWord;
PByte = ^Byte;
var
currptr: pointer;
i: byte;
begin
currptr := inbuffer;
Result := crc;
while buffersize 4 do
begin
Result := Result xor PDWord(currptr)^;
inc(Longint(currptr), 4);
Result := (Result shr 8) xor Crc32Tab[Byte(Result)];
Result := (Result shr 8) xor Crc32Tab[Byte(Result)];
Result := (Result shr 8) xor CRC32Tab[Byte(Result)];
Result := (Result shr 8) xor crc32Tab[Byte(Result)];
dec(buffersize, 4);
end;
for i := 1 to buffersize do
begin
Result := CRC32tab[Byte(Result xor DWord(PByte(currptr)^))] xor (Result shr 8);
inc(Longint(currptr), 1);
end;
end;
Function CRCend( crc : DWord ): DWord;
begin
CRCend := (crc xor CRCSeed);
end;
end.
Use:
CODE
{$APPTYPE CONSOLE}
program crcmain; uses d3_crc32, sysutils, windows;
{ take CRC-32 of file in input }
var
infile: file;
crcvalue: DWord;
inbuffer: array[1..32768] of byte;
amount_read: integer;
begin
AssignFile(infile, 'crccopy.txt');
Reset(infile, 1);
crcvalue := crcseed;
blockread(infile, inbuffer, Sizeof(inbuffer), amount_read);
repeat
crcvalue := crc32_update(@inbuffer, amount_Read, crcvalue);
blockread(infile, inbuffer, Sizeof(inbuffer), amount_read);
until amount_read = 0;
CloseFile(infile);
crcvalue := crcend(crcvalue);
writeln('CRC-32 Hex: ', IntToHex(crcvalue, 8));
readln;
end.
]]>