Package dev.brachtendorf.jimagehash.hashAlgorithms

Class HashBuilder

  • public class HashBuilder
extends Object
    Helper class to quickly create a bitwise byte array representation which can be converted to a big integer object.

    To maintain the capability to decode the created hash value back to an image the order of the byte array is of utmost importance. Due to hashes ability to contain non 8 compliment bit values and BigInteger stripping leading zero bits the partial bit value has to be present at the 0 slot.

    The hashbuilder systematically grows the base byte[] array as needed but performs the best if the correct amount of bits are known beforehand.

    In other terms this class performs the same operation as 

     
        StringBuilder sb = new StringBuilder();
        sb.append("100011");
        BigInteger b = new BigInteger(sb.toString(),2);
    But scales much much better for higher hash values. The order of the bits are flipped using the hashbuilder approach.
    Since:
    3.0.0
    Author:
    Kilian TODO we don't really need a Big Integer at all. We can use a byte array.

    • Field Detail

      • length

        protected int length

    • Constructor Detail

      • HashBuilder

        public HashBuilder​(int bits)
        Create a hashbuilder.
        Parameters:
        bits - the number of bits the hash will have [8 - Integer.MAX_VALUE]. If the builder requires more space than specified copy operations will take place to grow the builder automatically.

        Allocating to much space also results in the correct hash value being created but might also result in a slight performance penalty

    • Method Detail

      • prependZero

        public void prependZero()
        Add a zero bit to the hash

      • prependOne

        public void prependOne()
        Add a one bit to the hash

      • toBigInteger

        public BigInteger toBigInteger()
        Convert the internal state of the hashbuilder to a big integer object
        Returns:
        a big integer object