Bit mask required to be used when mapping logical keys into physical keys using Aerospike block storage technique

bitMaskCreationForBlockStorage.java

    /**
     * Obtain bit mask required to ensure we have on average a specific number of logical objects in each physical object
     * @param keySpaceSize - size of key space
     * @param objectsPerBlock - average number of objects stored in each physical object
     * @return bit mask as a BigInteger
     */
    public static BigInteger getBitMask(long keySpaceSize,int objectsPerBlock){
        // No of bits required is
        // log(keySpaceSize/objectsPerBlock) / log(2)
        // as reqd # of keys is keySpaceSize/objectsPerBlock
        // round up as bit count has to be integral
        int bitMaskSize = (int)Math.ceil((Math.log(keySpaceSize/objectsPerBlock) / Math.log(2)));
        // Bit mask - 2^mask size - 1 to get all bits set
        return (new BigInteger("2")).pow(bitMaskSize).subtract(new BigInteger("1"));
    }