this is driving me battier than i already am :(
i have a binary file that contains a record of data... the first field of the
data is a crc32 value of a string of characters... the string of characters is
lower cased before being fed to the crc32 function... i need to calculate the
same crc32 value as what is stored in the file...
i've already checked the polynomial ($edb88320) is the same in both, the
original implementation (converted to TP4 in 1988) and this implementation...
the original routine uses longint and speaks of initializing the variable to
$ffffffff before feeding it to the crc32 routine... the existing routine in FPC
says "Pre- and post-conditioning (one's complement) is performed within this
function so it shouldn't be done by the application." but that doesn't give me
the proper answer in this case... i've tried using cardinal types and longint
types to no avail...
the following is so so so very close but now i'm bald headed, completely lost in
the deep dark woods and can't find my breadcrumbs any more :(
program damncrc32;
{$MODE OBJFPC}
{$DEFINE DYNAMIC_CRC_TABLE}
uses
crc, sysutils;
const
mystring : pchar = 'aaaaaaaa aaaaaaaa';
// desired crc32 checksum value 0xd728cba6
// crc32 as seen in binary file 0xcba6d728
// mystrsum : cardinal = 3609775014; // crc32 in decimal
mystrsum : longint = -685192282; // crc32 in decimal
var
// mycrc32 : cardinal;
mycrc32 : longint;
mystrln : longint;
counter : longint;
begin
// set the string length - subtract 1 later!
mystrln := length(mystring);
// prime the crc32 variable
mycrc32 := crc32(0, nil, 0);
// mycrc32 := $ffffffff;
// mycrc32 := -1;
// now calculate the crc32 of the string
for counter := 0 to mystrln-1 do
begin
mycrc32 := crc32(mycrc32, @mystring[counter], 1);
writeln('mystring[',inttostr(counter),'] : ',mystring[counter],'
',hexstr(mycrc32,8));
end;
// write the string and its length
writeln('mystring : ',mystring,' length : ',mystrln);
// write the desired crc32 in decimal, hex and inverted hex
writeln(' desired crc32 : ',mystrsum:12,' (normal 0x',hexstr(mystrsum,8),'
- inverted 0x',hexstr(swap(mystrsum),8),')');
// write the result crc32 in decimal, hex and inverted hex
writeln(' result crc32 : ',mycrc32:12,' (normal 0x',hexstr(mycrc32,8),' -
inverted 0x',hexstr(swap(mycrc32),8),')');
// did we get it right???
write('crc32 checksum');
if mycrc32 <> mystrsum then
writeln(' DOES NOT match.')
else
writeln(' matches! YAY!!!');
end.
_______________________________________________
fpc-pascal maillist - fpc-pascal@lists.freepascal.org
http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
