>I am trying to create checksum function like SYS(2007) maybe somebody knows what math behind this one

I found this reference searching on MSDN:

SYS(2007) Algorithm for Checksum
Article ID: Q101289

The information in this article applies to:
Microsoft FoxPro for Windows, versions 2.5, 2.5a, and 2.5b
Microsoft FoxPro for MS-DOS, versions 2.0, 2.5, 2.5a, and 2.5b
Microsoft FoxPro for Macintosh, version 2.5b
The SYS(2007) function returns the checksum value of the character expression . The correct syntax is SYS(2007,). A checksum can be used to test the validity of data or to compare two character expressions.

NOTE: Checksum is a "byte-oriented CRC-16" algorithm. The exact logic was last published in the February 1986 edition of "Dr. Dobbs Journal."

Additional reference words: FoxMac FoxDos FoxWin 2.00 2.50 2.50a 2.50b check sum KBCategory: kbprg KBSubcategory: FxprgGeneral