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Delphi - crc-16


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crc over one byte

procedure ByteCrc(data:byte;var crc:word); VAR i:BYTE; BEGIN FOR i:=0 TO 7 DO BEGIN IF ((data and $01)XOR(crc AND $0001)<>0) THEN BEGIN crc:=crc shr 1; crc:= crc XOR $A001; END ELSE crc:=crc shr 1; data:=data shr 1; // this line is not ELSE and executed anyway. END; END;

crc over the string

the crc as result is initialized as zero, then each byte is processed. function StringCrc(s:shortstring):word; var len,i:integer; begin result:=0; len:=length(s); for i:=1 to len do bytecrc(ord(s[i]),result); end;


The data is filled into a shortstring as : crcstring:shortstring:=chr(data[1])+..+chr(data[N]); MyCrc:word:=StringCrc(crcstring);


This crc is calculated as X^16+X^15+X^2+1 and can 
protect 2^16 bits or 8192 bytes against single bit 
errors. For longer datablocks, the crc-32 is to be 

This the slow implementation requiring little RAM.
There also exists a fast implementation requiring 
more RAM to hold a table. One byte is processed in
a few assembly instructions.

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last updated: 23.june.99

Copyright (99,2000) Ing.Büro R.Tschaggelar