babysimon

Hi. My colleague XXXXXXXX gave me your email address. I'm looking at the format of XXXXXX sales files - specifically the CRC on the header line.

The document "XXXXXXXX Retail Interfaces" states that the CRC is "the one's complement of the total number of bytes in the file excluding the header". However, my understanding of a CRC (Cyclic Redundancy Checksum) is that it is a 16- or 32-bit hash value calculated from the file contents.

The example files you've sent us have an 18-digit (72-bit) hexadecimal number as the first line. This doesn't appear to match either definition.

The file XXXXXXXXX has a header line of "0002527b00001e363e" - according to "XXXXXXXXXX Retail Interfaces", the file size should be FFFDAD84FFFFE1C9C1 or 18,446,090 Terabytes.

Could you explain how this value is calculated please?

Thanks for your help,

Simon MacMullen