The hexToDec operator converts a hexadecimal string of 16 or fewer characters to a long data type using Two's Complement for negative values.
hexToDec("<hexadecimal string>") as <field>
hexToDec(<hexadecimal_field>) as <field>
The following returns
V with a value of
| hexToDec("0000000000001337") as V
... | count by _collector | decToHex(_count) as v | hexToDec(v) as h
... | count by _collector | where _count = hexToDec("7AF")