CREATE TEMP FUNCTION
hex64ToInt64(hex STRING)
RETURNS INT64 AS (
IF(hex < "8000000000000000",
cast(concat("0x", hex) AS INT64),
(SELECT (((ms32 & 0x7fffffff) << 32) | ls32) - 0x7fffffffffffffff - 1
FROM (SELECT cast(concat("0x", substr(hex, 1, 8)) AS INT64) AS ms32,
cast(concat("0x", substr(hex, 9, 8)) AS INT64) AS ls32))));