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From mengxr <...@git.apache.org>
Subject [GitHub] spark pull request: [SPARK-14850][ML] convert primitive array from...
Date Thu, 28 Apr 2016 08:07:25 GMT
Github user mengxr commented on a diff in the pull request:

    https://github.com/apache/spark/pull/12640#discussion_r61387937
  
    --- Diff: sql/catalyst/src/main/java/org/apache/spark/sql/catalyst/expressions/UnsafeArrayData.java
---
    @@ -336,4 +336,62 @@ public UnsafeArrayData copy() {
         arrayCopy.pointTo(arrayDataCopy, Platform.BYTE_ARRAY_OFFSET, sizeInBytes);
         return arrayCopy;
       }
    +
    +  public int[] toPrimitiveIntArray() {
    +    int[] result = new int[numElements];
    +    Platform.copyMemory(baseObject, baseOffset + 4 + 4 * numElements,
    +      result, Platform.INT_ARRAY_OFFSET, 4 * numElements);
    +    return result;
    +  }
    +
    +  public double[] toPrimitiveDoubleArray() {
    +    double[] result = new double[numElements];
    +    Platform.copyMemory(baseObject, baseOffset + 4 + 4 * numElements,
    +      result, Platform.DOUBLE_ARRAY_OFFSET, 8 * numElements);
    +    return result;
    +  }
    +
    +  public static UnsafeArrayData fromPrimitiveArray(int[] arr) {
    +    int offsetRegionSize = 4 * arr.length;
    +    int valueRegionSize = 4 * arr.length;
    +    int totalSize = 4 + offsetRegionSize + valueRegionSize;
    +    byte[] data = new byte[totalSize];
    +
    +    Platform.putInt(data, Platform.BYTE_ARRAY_OFFSET, arr.length);
    +
    +    int elementOffsetStart = 4 + offsetRegionSize;
    +    for (int i = 0; i < arr.length; i++) {
    +      Platform.putInt(data, Platform.BYTE_ARRAY_OFFSET + 4 + i * 4, elementOffsetStart
+ i * 4);
    --- End diff --
    
    This has two multiplications per element, which is expensive. Try:
    
    ~~~java
    int regionOffset = Platform.BYTE_ARRAY_OFFSET + 4
    int elementOffset = elementOffsetStart
    for (...) {
      Platform.putInt(data, regionOffset, elementOffset);
      regionOffset += 4;
      elementOffset += 4;
    }
    ~~~


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