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#define POLY 0x8408
/*
// 16 12 5
// this is the CCITT CRC 16 polynomial X + X + X + 1.
// This works out to be 0x1021, but the way the algorithm works
// lets us use 0x8408 (the reverse of the bit pattern). The high
// bit is always assumed to be set, thus we only use 16 bits to
// represent the 17 bit value.
*/
unsigned short crc16(unsigned char *data_p, size_t length)
{
unsigned char i;
unsigned int data;
if ( length == 0 ) return 0;
unsigned int crc = 0xFFFF;
do
{
data = *data_p++;
for ( i=0; i < 8; i++ )
{
if ( (crc ^ data) & 1 )
crc = (crc >> 1) ^ POLY;
else
crc >>= 1;
data >>= 1;
}
} while ( --length != 0 );
crc = ~crc;
data = crc;
crc = (crc << 8) | ((data >> 8) & 0xff);
return (unsigned short)(crc);
}
const POLY = $8408;
function crc16( ; data_p: PByte; length:size_t ):word;
var
i : byte;
data, crc: word;
begin
if ( length = 0 ) then
begin
result:= 0;exit;
end;
crc := $FFFF;
repeat
data := data_p^;
inc(data_p);
for ( i:=0 to 8-1 do ) do
begin
if ( (crc xor data) and 1 ) > 0 then
crc := (crc shl 1) xor POLY
else
crc := crc shr 1;
data := data shr 1;
end;
dec(length);
until ( length = 0 );
crc := crc not crc;
data := crc;
crc := (crc shl 8) or ((data shr 8) and $ff);
result := crc;
end;
看看对不？好久没看C了
type
PWord=^word;
function crc16(data_p:PWord;length:integer):word;
const
POLY=$8408;
var
i:integer;
crc,data:word;
begin
result:=0;
if ( length = 0 ) then
exit;
crc:= $FFFF;
repeat
data := data_p^;
inc(data_p);
for i:=0 to 7 do
begin
if (( crc xor data) and 1 <>0 ) then
crc := (crc shr 1) xor POLY
else
crc:= crc shr 1;
data := data shr 1;
end;
dec(length);
until length<>0;
crc := not crc;
data := crc;
crc := (crc shl 8) or ((data shr 8) and $ff);
result:=crc;
end;
const
POLY =$8408;
type
PBYTE=^Byte;
//unsigned short crc16(unsigned char *data_p, size_t length)
function crc16(data_p:PBYTE;length:UINT):Byte;
//{
// unsigned char i;
// unsigned int data;
var
i:Byte;
data:UINT;
crc:UINT;
begin
//if ( length == 0 ) return 0;
Result:=0;
if length=0 then exit;
//unsigned int crc = 0xFFFF;
crc:=$FFFF;
//do
repeat
//{
//data = *data_p++;
data:=data_p^;
//for ( i=0; i < 8; i++ )
for i:=0 to 8-1 do
//{
begin
//if ( (crc ^ data) & 1 )
if ((crc xor data) and 1) <>0 then
//crc = (crc >> 1) ^ POLY;
crc:=(crc shr 1) xor POLY
else
//crc >>= 1;
crc:=crc shr 1;
//data >>= 1;
data := data shr 1;
//}
end;
dec(length);
//} while ( --length != 0 );
until length=0;
//crc = ~crc;
crc:= (not crc);
//data = crc;
data:=crc;
//crc = (crc << 8) | ((data >> 8) & 0xff);
crc:=(crc shl 8) or ((data shr 8) and $ff);
//return (unsigned short)(crc);
Result:=crc;
//}
end;
