JCL Help:InitCrc16@Word@Word
JCL Help: InitCrc16 Function
Search in JCL Help
Search in all projects
Summary
Defines a new polynomial and starting value for the 16 bit CRC functions.
Pascal
procedure InitCrc16(Polynom: Word; Start: Word); overload;
procedure InitCrc16(Polynom: Word; Start: Word; out Crc16Table: TCrc16Table); overload;
Parameters
| Parameters | Description |
| Start: Word | 16 bit starting value to be used with subsequent calls to 16 bit CRC functions. |
| Polynomial | Generator polynomial to be used with subsequent calls to 16 bit CRC functions. The polynomial is given without the highest bit (bit x^16). |
Description
Defines a new "generator polynomial" and starting value for the 16 bit CRC functions. Beware that the check and the correction only works if the polynomial is "appropriate". Two of these polynomials are predefined: Crc16PolynomCCITT = $1021 represents the polynomial x^16 + x^12 + x^5 + 1 that is suggested by the CCITT and used to protect floppy disks. Crc16PolynomXXXXX = $8005 represents the polynomial x^16 + x^15 + x^2 + 1 which is another "appropriate" polynomial and used to protect magnetic tapes. Beware that not appropriate polynomials result in highly undesirable behaviour of the CRC. The starting value can by anything. $FFFF and 0 are usual definitions.
See Also
About
Unit
Donator
Michael Schnell
Notes
As a standard in the JEDI Code Library the compiler option {$J-} is set to prevent modifying typed constants. So the function CRC32Init only exists if JCLMath is recompiled with the compiler environment variable "CRCINIT" defined, which temporarily sets {$J+} for the CRC functions.
Contribute to this help topic
This documentation wiki is based on the collaborative effort of Project JEDI users. Your edits are welcome in order to improve documentation quality: edit this page
