org.apache.hadoop.hive.ql.udf.UDFReverse Maven / Gradle / Ivy
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* to you 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,
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* See the License for the specific language governing permissions and
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*/
package org.apache.hadoop.hive.ql.udf;
import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.hive.ql.udf.generic.GenericUDFUtils;
import org.apache.hadoop.io.Text;
/**
* UDFReverse.
*
*/
@Description(name = "reverse", value = "_FUNC_(str) - reverse str", extended = "Example:\n"
+ " > SELECT _FUNC_('Facebook') FROM src LIMIT 1;\n" + " 'koobecaF'")
public class UDFReverse extends UDF {
private final Text result = new Text();
/**
* Reverse a portion of an array in-place.
*
* @param arr
* The array where the data will be reversed.
* @param first
* The beginning of the portion (inclusive).
* @param last
* The end of the portion (inclusive).
*/
private void reverse(byte[] arr, int first, int last) {
for (int i = 0; i < (last - first + 1) / 2; i++) {
byte temp = arr[last - i];
arr[last - i] = arr[first + i];
arr[first + i] = temp;
}
}
public Text evaluate(Text s) {
if (s == null) {
return null;
}
// set() will only allocate memory if the buffer of result is smaller than
// s.getLength() and will never resize the buffer down.
result.set(s);
// Now do an in-place reversal in result.getBytes(). First, reverse every
// character, then reverse the whole string.
byte[] data = result.getBytes();
int prev = 0; // The index where the current char starts
for (int i = 1; i < result.getLength(); i++) {
if (GenericUDFUtils.isUtfStartByte(data[i])) {
reverse(data, prev, i - 1);
prev = i;
}
}
reverse(data, prev, result.getLength() - 1);
reverse(data, 0, result.getLength() - 1);
return result;
}
}