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From dumindux <...@git.apache.org>
Subject [GitHub] phoenix pull request: PHOENIX-1875 ARRAY_PREPEND function implemen...
Date Tue, 05 May 2015 01:30:03 GMT
Github user dumindux commented on a diff in the pull request:

    https://github.com/apache/phoenix/pull/79#discussion_r29639284
  
    --- Diff: phoenix-core/src/main/java/org/apache/phoenix/schema/types/PArrayDataType.java
---
    @@ -543,6 +544,151 @@ private static void writeEndBytes(byte[] array, int newOffsetArrayPosition,
int
             Bytes.putByte(array, newOffsetArrayPosition + offsetArrayLength + byteSize +
2 * Bytes.SIZEOF_INT, header);
         }
     
    +    public static boolean prependItemToArray(ImmutableBytesWritable ptr, int length,
int offset, byte[] arrayBytes, PDataType baseType, int arrayLength, Integer maxLength, SortOrder
sortOrder) {
    +        int elementLength = maxLength == null ? ptr.getLength() : maxLength;
    +        if (ptr.getLength() == 0) {
    +            elementLength = 0;
    +        }
    +        //padding
    +        if (elementLength > ptr.getLength()) {
    +            baseType.pad(ptr, elementLength, sortOrder);
    +        }
    +        int elementOffset = ptr.getOffset();
    +        byte[] elementBytes = ptr.get();
    +
    +        byte[] newArray;
    +        if (!baseType.isFixedWidth()) {
    +            int offsetArrayPosition = Bytes.toInt(arrayBytes, offset + length - Bytes.SIZEOF_INT
- Bytes.SIZEOF_INT - Bytes.SIZEOF_BYTE, Bytes.SIZEOF_INT);
    +            int offsetArrayLength = length - offsetArrayPosition - Bytes.SIZEOF_INT -
Bytes.SIZEOF_INT - Bytes.SIZEOF_BYTE;
    +            arrayLength = Math.abs(arrayLength);
    +
    +            //checks whether offset array consists of shorts or integers
    +            boolean useInt = offsetArrayLength / arrayLength == Bytes.SIZEOF_INT;
    +            boolean convertToInt = false;
    +            int endElementPosition = getOffset(arrayBytes, arrayLength - 1, !useInt,
offsetArrayPosition + offset) + elementLength + Bytes.SIZEOF_BYTE;
    +            int newOffsetArrayPosition;
    +            int offsetShift;
    +            int firstNonNullElementPosition = 0;
    +            int currentPosition = 0;
    +            //handle the case where prepended element is null
    +            if (elementLength == 0) {
    +                int nulls = 1;
    +                //counts the number of nulls which are already at the beginning of the
array
    +                for (int index = 0; index < arrayLength; index++) {
    +                    int currOffset = getOffset(arrayBytes, index, !useInt, offsetArrayPosition
+ offset);
    +                    if (arrayBytes[offset + currOffset] == QueryConstants.SEPARATOR_BYTE)
{
    +                        nulls++;
    +                    } else {
    +                        //gets the offset of the first element after nulls at the beginning
    +                        firstNonNullElementPosition = currOffset;
    --- End diff --
    
    firstNonNullElementPosition is used to know how many bytes are there before the first
non null element in the original array bytes(that is number of bytes used to represent nulls
at the beginning). when calculating the new array bytes length, bytes required for storing
nulls at the beginning is calculated(nMultiplesOver255 + bytesForRemainingNulls + Bytes.SIZEOF_BYTE)
and added to the original array bytes length(length with all the bytes) then firstNonNullElementPosition
is subtracted from it to subtract the number of bytes used to represent nulls at the beginning
in the original array(since those are included in the original array bytes length)


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