cw_round_half_even.sqlx

config { hasOutput: true }
/*
 * Copyright 2022 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.
 */

CREATE OR REPLACE FUNCTION ${self()}(n BIGNUMERIC, d INT64) RETURNS NUMERIC AS (
  CAST(
    -- if both arguments to POW are INT then it returns FLOAT and it messes up entire calculation for big numbers
    -- hence we changed 'd' to be BIGNUMERIC so that we force POW to return BIGNUMERIC
    POW(10, -CAST(d AS BIGNUMERIC)) * SIGN(n) *
    CASE WHEN MOD(TRUNC(n * POW(10, CAST(d AS BIGNUMERIC))), 2) = 0 -- even number
       THEN CEIL(ABS(n * POW(10, CAST(d AS BIGNUMERIC))) - 0.5) -- round towards
       ELSE FLOOR(ABS(n * POW(10, CAST(d AS BIGNUMERIC))) + 0.5) -- round away
    END
    AS NUMERIC)
);