Github user davies commented on a diff in the pull request:

    https://github.com/apache/spark/pull/6804#discussion_r32376753
  
    --- Diff: 
unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java ---
    @@ -131,24 +131,31 @@ public boolean contains(final UTF8String substring) {
         }
     
         for (int i = 0; i <= bytes.length - b.length; i++) {
    -      // TODO: Avoid copying.
    -      if (bytes[i] == b[0] && Arrays.equals(Arrays.copyOfRange(bytes, i, i 
+ b.length), b)) {
    +      if (bytes[i] == b[0] && startsWith(substring, i)) {
             return true;
           }
         }
         return false;
       }
     
    +  private boolean startsWith(final UTF8String prefix, int offset) {
    +    byte[] b = prefix.getBytes();
    +    if (b.length + offset > bytes.length || offset < 0) {
    +      return false;
    +    }
    +    int i = 0;
    +    while (i < b.length && b[i] == bytes[i + offset]) {
    +      i++;
    +    }
    +    return i == b.length;
    +  }
    +
       public boolean startsWith(final UTF8String prefix) {
    -    final byte[] b = prefix.getBytes();
    -    // TODO: Avoid copying.
    -    return b.length <= bytes.length && 
Arrays.equals(Arrays.copyOfRange(bytes, 0, b.length), b);
    +    return startsWith(prefix, 0);
    --- End diff --
    
    Right now, UTF8String is only used by catalyst, can it will check prefix is 
null or not. Since this is a public method, it's still good to check prefix is 
null or not.


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