JCL Help:Crc32@TCrc32Table@array of Byte@Integer@Cardinal
JCL Help: Crc32 Function
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Summary
Calculates or checks a 32 Bit CRC.
Pascal
function Crc32_P(X: PJclByteArray; N: Integer; Crc: Cardinal = 0): Cardinal; overload;
function Crc32(const X: array of Byte; N: Integer; Crc: Cardinal = 0): Cardinal; overload;
function Crc32(const Crc32Table: TCrc32Table; const X: array of Byte; N: Integer; Crc: Cardinal = 0): Cardinal; overload;
function Crc32_A(const Crc32Table: TCrc32Table; const X: array of Byte; Crc: Cardinal = 0): Cardinal; overload;
Parameters
| Parameters | Description |
| X: PJclByteArray | The array which contains the data. With Crc32 and Crc32_A this is an open array parameter, with CrC32_P this is a pointer to the first byte of the array of bytes. |
| N: Integer | The number of elements in X. Crc32_A calculates the checksum of all bytes in the array X. |
| Crc: Cardinal = 0 | (optional) if not defined or = 0: Crc32 calculates the CRC for the data array transmitted; if CRC is defined: the CRC value is checked against the data and the result is 0 if the CRC was correct. |
Return Value
- If on input CRC not defined or = 0: The result is the created CRC.
- If on input CRC is defined: The result is 0 if the CRC was OK,otherwise the function returns the residuum for the correction function.
Description
32 Bit CRC function. Calculates or checks a CRC. Independently from the size of the data array, with a 32 bit CRC any single and double bit error can be detected. By far most multiple bit errors are detected, too: E.g. all even (or odd) count of bit errors (depending on the polynomial used) and all burst errors with up to 32 bits length (so any sequence of up to 4 incorrect bytes) are detected. Burst error with a length of more than 32 are detected with a probability of 99,9999999767 %. All this is true only if an appropriate polynomial is used. By default the 32 Bit CRC "generator polynomial" suggested by the CCITT is used: x^32 + x^26 + x^23 + x^22 + x^16 + x^12 + x^11 + x^10 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1 ($104C11DB7). This polynomial has a "maximum cycle" and is used by Ethernet and Zip, too. The default starting value is $FFFFFFFF. By InitCrc32 a different polynomial and starting value can be defined.
See Also
About
Unit
Donator
Michael Schnell
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