Fill.cs

public static unsafe byte[] Fill(this byte[] array, int offset, int length, byte value)
{
    if ((length <= 0) || (array == null))
    {
        return array;
    }

    fixed (byte* pSrc = &array[offset])
    {
        *pSrc = value;
        byte* pDst;

        int copy;
        for (copy = 1; copy <= length / 2; copy <<= 1)
        {
            pDst = pSrc + copy;
            Buffer.MemoryCopy(pSrc, pDst, length - copy, copy);
        }

        pDst = pSrc + copy;
        Buffer.MemoryCopy(pSrc, pDst, length - copy, length - copy);
    }

    return array;
}