An attempt to understand byte and bit ordering in redis bitsets

redisBitSetTests.java

import java.util.Arrays;
import java.util.BitSet;

import redis.clients.jedis.Jedis;

public class SieveOfEratosthenes {

    /**
     * @param args
     */
    public static void main(final String[] args) {

        // setup values
        final Jedis redis = new Jedis("localhost");
        final String sieveSetBit = "sieveSetBit";
        final String sieveSetKey = "sieveSetKey";
        final int length = 20;
        final BitSet sieve = new BitSet(length);
        sieve.flip(2, length);

        // create bitset of all values
        for (int i = 0; i < length; i++) {
            if (sieve.get(i)) {
                for (int j = i * 2; j < length; j += i) {
                    sieve.set(j, false);
                }
            }
        }

        // Write 2 bitsets to redis
        // 1. setbit through redis
        for (int i = 0; i < sieve.length(); i++) {
            if (sieve.get(i)) {
                redis.setbit(sieveSetBit, i, true);
            }
        }

        // 2. Set entire bitset
        redis.set(sieveSetKey.getBytes(), sieve.toByteArray());

        // Compare bitsets from Redis when retrieved via getKey
        final String sieveBitString = redis.get(sieveSetBit);
	final String sieveKeyString = redis.get(sieveSetKey);
	final byte[] sieveBitBytes = redis.get(sieveSetBit.getBytes());
	final byte[] sieveKeyBytes = redis.get(sieveSetKey.getBytes());
        final BitSet setBitSieve = BitSet.valueOf(sieveBitString.getBytes());
        final BitSet setKeySieve = BitSet.valueOf(sieveKeyString.getBytes());
        final BitSet reverseSetBit = fromByteArray(sieveBitString.getBytes());
        final BitSet reverseSetKey = fromByteArray(sieveKeyString.getBytes());

	System.out.println(Arrays.toString(sieve.toByteArray()));
	System.out.println(sieve + " <== Original Sieve");
	System.out.println();
	System.out.println(Arrays.toString(sieveBitString.getBytes()));
        System.out.println(setBitSieve + " <== setbit/get (String) -> BitSet.valueOf()");
        System.out.println(reverseSetBit + " <== setbit/get (String) -> fromByteArray()");
	System.out.println();
	System.out.println(Arrays.toString(sieveKeyString.getBytes()));
        System.out.println(setKeySieve + " <== set/get (String) -> BitSet.valueOf()");
        System.out.println(reverseSetKey + " <== set/get (String) -> fromByteArray()");
	System.out.println();
	System.out.println(Arrays.toString(sieveKeyBytes));
	System.out.println(BitSet.valueOf(sieveKeyBytes) + " <== get/set (byte[] versions) -> BitSet.valueOf()");
	System.out.println();
	System.out.println(Arrays.toString(sieveBitBytes));
	System.out.println(BitSet.valueOf(sieveBitBytes) + " <== setbit/get (byte[] versions) -> BitSet.valueOf()");
	System.out.println(fromByteArrayReverse(sieveBitBytes) + " <== setbit/get (byte[] versions) -> fromByteArrayReverse()");
    }

    public static BitSet fromByteArrayReverse(final byte[] bytes) {
        final BitSet bits = new BitSet();
        for (int i = 0; i < bytes.length * 8; i++) {
	    if ((bytes[i / 8] & (1 << (7 - (i % 8)))) != 0) {
                bits.set(i);
            }
        }
        return bits;
    }
    
    public static BitSet fromByteArray(final byte[] bytes) {
        final BitSet bits = new BitSet();
        for (int i = 0; i < bytes.length * 8; i++) {
            if ((bytes[bytes.length - i / 8 - 1] & (1 << (i % 8))) > 0) {
                bits.set(i);
            }
        }
        return bits;
    }
}