{
SAM LEVENTER
> I'm not quite sure how CRC's work. I have routines For calculating both
> 16-bit and 32-bit CRC values, however, they seem to be only For one Byte.
> How would I go about calculating the 16-bit CRC of an entire File?
CRCs are CYCLIC redundancy codes. That means that you cycle through the
entire File, ORing it With the old CRC.
Just call updateCRC in the below Unit.
This Program is donated to the Public
Domain by MarshallSoft Computing, Inc.
It is provided as an example of the use
of the Personal Communications Library.
}
Unit mycrc16;
Interface
Function UpdateCRC(crc:Word;data:Byte):Word;
Implementation
Const
POLY = $1021;
Var
CRCtable : Array [0..255] of Word;
{ compute updated CRC }
Function UpdateCRC(crc : Word; data : Byte) : Word;
begin
UpDateCRC := (crc SHL 8) xor (CRCtable[(crc SHR 8) xor data]);
end;
{ initialize CRC table }
Procedure InitCRC;
Var
i : Integer;
{ calculate CRC table entry }
Function CalcTable(data, genpoly, accum : Word) : Word;
Var
i : Word;
begin
data := data SHL 8;
For i := 8 downto 1 do
begin
if ((data xor accum) and ($8000 <> 0)) then
accum := (accum SHL 1) xor genpoly
else
accum := accum SHL 1;
data := data SHL 1;
end;
CalcTable := accum;
end;
begin
For i := 0 to 255 do
CRCtable[i] := CalcTable(i, POLY, 0);
end;
begin
InitCRC;
end.