from_hex.sqlx

config { hasOutput: true }
/*
 * Copyright 2020 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

-- from_hex:
-- Input: STRING representing a number in hexadecimal form
-- Output: INT64 number in decimal form
CREATE OR REPLACE FUNCTION ${self()}(value STRING) 
OPTIONS (
    description="Returns a number in decimal form from its hexadecimal representation."
)
AS
(
  (
    SELECT 
      SUM(
      	CAST(
      	  CONCAT('0x', SUBSTR(value, byte * 2 + 1, 2)) 
      	    AS INT64) << ((LENGTH(value) - (byte + 1) * 2) * 4))
    FROM UNNEST(GENERATE_ARRAY(1, LENGTH(value) / 2)) WITH OFFSET byte
  )
);