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From davies <...@git.apache.org>
Subject [GitHub] spark pull request: [SPARK-8301][SQL] Improve UTF8String substring...
Date Sun, 14 Jun 2015 06:15:22 GMT
Github user davies commented on a diff in the pull request:

    https://github.com/apache/spark/pull/6804#discussion_r32376747
  
    --- 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]) {
    --- End diff --
    
    As @rxin suggested, we could use unsafe API to compare 8 bytes at once. But I think in
most cases the suffix will be short and this while loop will terminate very fast, it may not
worth that complication.
    
    The while loop is good to me.


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