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/**
 * Copyright (c) 2016-2022 Deephaven Data Labs and Patent Pending
 */
package io.deephaven.engine.table.impl.util.copy;

import io.deephaven.chunk.*;

import io.deephaven.chunk.attributes.Any;

public class CharCopyKernel implements CopyKernel {
    public static final CharCopyKernel INSTANCE = new CharCopyKernel();

    private CharCopyKernel() {} // use through the instance

    /**
     * Copy values from baseInput / overInput into output.
     * 
     * Pseudo-implementation: output[i] = useOverInput.forBit(i) ? overInput[i] : baseInput[i];
     * 
     * Note that useOverInput should cover the same data range as baseInput such that
     * {@code useOverInput.length == (overInput.length + 63) / 64} is true.
     *
     * @param output       the output chunk
     * @param baseInput    the input array to use when bit in useOverInput is zero (array)
     * @param overInput    the input array to use when bit in useOverInput is one (array)
     * @param useOverInput the bitset array to indicate whether to use baseInput or overInput for each element
     * @param srcOffset    the offset in baseInput/overInput
     * @param dstOffset    the offset in output
     * @param length       the number of elements to copy
     */
    public static  void conditionalCopy(
            WritableCharChunk output, char[] baseInput, char[] overInput, long[] useOverInput,
            int srcOffset, int dstOffset, int length)
    {
        int bitsSet = 0;
        final int bitsetLen = (length + 63) >> 6;
        final int bitsetOffset = srcOffset >> 6;
        for (int i = 0; i < bitsetLen; ++i) {
            bitsSet += Long.bitCount(useOverInput[i + bitsetOffset]);
        }
        final int totalBits = bitsetLen << 6;
        final boolean flipBase = bitsSet > totalBits / 2;

        // mem-copy from baseline
        output.copyFromTypedArray(flipBase ? overInput : baseInput, srcOffset, dstOffset, length);

        final int srcEndOffset = srcOffset + length;
        for (int ii = CopyKernel.Utils.nextSetBit(useOverInput, srcOffset, srcEndOffset, flipBase);
             ii < srcEndOffset;
             ii = CopyKernel.Utils.nextSetBit(useOverInput, ii + 1, srcEndOffset, flipBase)) {
            output.set(dstOffset + ii - srcOffset, flipBase ? baseInput[ii] : overInput[ii]);
        }
    }

    @Override
    public  void conditionalCopy(
            WritableChunk output, Object baseInput, Object overInput, long[] useOverInput,
            int srcOffset, int dstOffset, int length)
    {
        char[] typedBaseInput = (char[]) baseInput;
        char[] typedOverInput = (char[]) overInput;
        conditionalCopy(output.asWritableCharChunk(), typedBaseInput, typedOverInput, useOverInput, srcOffset, dstOffset, length);
    }
}