// the constants here are for the crc-32 generator  
// polynomial, as defined in the microsoft  
// systems journal, march 1995, pp. 107 - 108  
  
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);  
  
type  
//----------------------------------crc32----------------------------------  
{$ifdef ver130} // this is a bit awkward  
// 8-byte integer  
tinteger8 = int64; // delphi 5  
{$else}  
{$ifdef ver120}  
tinteger8 = int64; // delphi 4  
{$else}  
tinteger8 = comp; // delphi 2 or 3  
{$endif}  
{$endif}  
//----------------------------------crc32----------------------------------  
  
  
// use calccrc32 as a procedure so crcvalue can be passed in but  
// also returned. this allows multiple calls to calccrc32 for  
// the "same" crc-32 calculation.  
procedure calccrc32(p: pointer; bytecount: dword; var crcvalue: dword);  
// 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: dword;  
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 {calccrc32};  
  
function calcstringcrc32(s: string; out crc32: dword): boolean;  
var  
crc32table: dword;  
begin  
// verify the table used to compute the crcs has not been modified.  
// thanks to gary williams for this suggestion, jan. 2003.  
crc32table := $ffffffff;  
calccrc32(addr(table[0]), sizeof(table), crc32table);  
crc32table := not crc32table;  
  
if crc32table <> $6fcf9e13 then showmessage('crc32 table crc32 is ' +  
inttohex(crc32table, 8) +  
', expecting $6fcf9e13')  
else  
begin  
crc32 := $ffffffff; // to match pkzip  
if length(s) > 0 // avoid access violation in d4  
then calccrc32(addr(s[1]), length(s), crc32);  
crc32 := not crc32; // to match pkzip  
end;  
end;  
  
procedure calcfilecrc32(fromname: string; var crcvalue: dword;  
var totalbytes: tinteger8;  
var error: word);  
var  
stream: tmemorystream;  
begin  
error := 0;  
crcvalue := $ffffffff;  
stream := tmemorystream.create;  
try  
try  
stream.loadfromfile(fromname);  
if stream.size > 0 then calccrc32(stream.memory, stream.size, crcvalue)  
except  
on e: ereaderror do  
error := 1  
end;  
crcvalue := not crcvalue  
finally  
stream.free  
end;  
end;  
  
procedure tform1.button1click(sender: tobject);  
var  
s: string;  
crc32: dword;  
begin  
s := 'test string';  
if calcstringcrc32(s, crc32) then  
showmessage(inttostr(crc32));  
end;