// Update the CRC for transmitted and received data using
// the CCITT 16bit algorithm (X^16 + X^12 + X^5 + 1).

    unsigned char ser_data;
    static unsigned int crc;

    crc  = (unsigned char)(crc >> 8) | (crc << 8);
    crc ^= ser_data;
    crc ^= (unsigned char)(crc & 0xff) >> 4;
    crc ^= (crc << 8) << 4;
    crc ^= ((crc & 0xff) << 4) << 1;

    unsigned char ser_data;
    static unsigned int crc;

    crc  = (unsigned char)(crc >> 8) | (crc << 8);
    crc ^= ser_data;
    crc ^= (unsigned char)(crc & 0xff) >> 4;
    crc ^= (crc << 8) << 4;
    crc ^= ((crc & 0xff) << 4) << 1;

var ser_data:byte;
    crc:word;

begin
  crc:=(crc shr 8) or (crc shl 8);
  crc:=crc xor ser_data;
  crc:=crc xor ((crc and $00f0) shr 4);
  crc:=crc xor (crc shl 12);
  crc:=crc xor ((crc and $00ff) shl 5);
end;

01 05 FF 11 22 33 00 00 82 13  (CRC = 82 13)
FF 04 11 22 33 00 00 4B 08     (CRC = 4b 08)

#include "io8515.h"
RSEG CHECKSUM(1)
RSEG DEBUG(1)
;===============================================================;
; Calculate Flash code XModem CRC-CCITT ;
;===============================================================;
; EXTERN ByteCRC
CalcFlashCRC:
clr Z0
clr Z1
clr r16
clr r17

cal1: lpm ; Calculate CRC for next byte
mov r20,r0
rcall ByteCRC
adiw Z0,0x01
cpi Z0,low(SFB(CHECKSUM))
ldi r20,high(SFB(CHECKSUM))
cpc Z1,r20
brlo cal1

cal2: rjmp cal2 ; Flash CRC = DW 0x(r16:r17)

;---------------------------------------------------------------;
; Calculate one byte of XModem CRC-CCITT ;
; Function: int ByteCRC (int XmCRC,char Byte); ;
; Input: r17:r16 = Old value CRC-CCITT ;
; r20 = input byte ;
; Output: r17:r16 = New value CRC-CCITT ;
;---------------------------------------------------------------;
; PUBLIC ByteCRC
ByteCRC:eor r17,r20
ldi r21,8

bci1: lsl r16
rol r17
brcc bci2
ldi r20,0x10
eor r17,r20
ldi r20,0x21
eor r16,r20
bci2: dec r21
brne bci1
ret
;===============================================================;
END

unsigned long Crc32(unsigned char *buf, unsigned long len)
{
unsigned long crc_table[256];
unsigned long crc;

for (int i = 0; i < 256; i++)
{
crc = i;
for (int j = 0; j < 8; j++)
crc = crc & 1 ? (crc >> 1) ^ 0xEDB88320UL : crc >> 1;

crc_table[i] = crc;
};

crc = 0xFFFFFFFFUL;

while (len--)
crc = crc_table[(crc ^ *buf++) & 0xFF] ^ (crc >> 8);

return crc ^ 0xFFFFFFFFUL;
};

var data:array[0..$ffff] of byte;

{
подготовка массива data[]
}


{ Считает crc в массиве data[] от start до endd }
procedure CRC32(start,endd:word):dword;
var
crc_table:array [0..255] of dword;
crc:dword;
i,j:word;
begin
for i:=0 to 255 do begin
crc:=i;
for j:=0 to 7 do if (crc and 1)=1 then crc:=((crc shr 1) xor $EDB88320)
else crc:=crc shr 1;
crc_table[i]:=crc;
end;
crc:=$FFFFFFFF;
for i:=start to endd do begin
crc:=(crc_table[(crc xor data[i]) and $ff]) xor (crc shr 8);
end;
CRC32:=crc xor $FFFFFFFF;
end;

u16 r5_sum(unsigned char *b, u32 len)
{
register u32 i;
register u16 csum = 0;
for(i = 0; i < len; i++) {
   csum += (b[i] << 4);
   csum += (b[i] >> 4);
   csum *= 11;
}
  return csum;
}