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The Bouncy Castle Java APIs for CMS, PKCS, EAC, TSP, CMP, CRMF, OCSP, and certificate generation. This jar contains APIs for JDK 1.8 and up. The APIs can be used in conjunction with a JCE/JCA provider such as the one provided with the Bouncy Castle Cryptography APIs.

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package org.bouncycastle.tsp.ers;

import java.util.HashMap;
import java.util.Map;

import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import org.bouncycastle.operator.DigestCalculator;
import org.bouncycastle.util.Arrays;

/**
 * An ERSData object that caches hash calculations.
 */
public abstract class ERSCachingData
    implements ERSData
{
    private Map preCalcs = new HashMap();

    /**
     * Generates a hash for the whole DataGroup.
     *
     * @param digestCalculator the {@link DigestCalculator} to use for computing the hash
     * @return a hash that is representative of the whole DataGroup
     */
    public byte[] getHash(DigestCalculator digestCalculator, byte[] previousChainHash)
    {
        CacheIndex digAlgID = new CacheIndex(digestCalculator.getAlgorithmIdentifier(), previousChainHash);
        if (preCalcs.containsKey(digAlgID))
        {
            return (byte[])preCalcs.get(digAlgID);
        }

        byte[] hash = calculateHash(digestCalculator, previousChainHash);

        preCalcs.put(digAlgID, hash);

        return hash;
    }

    protected abstract byte[] calculateHash(DigestCalculator digestCalculator, byte[] previousChainHash);

    private static class CacheIndex
    {
        final AlgorithmIdentifier algId;
        final byte[] chainHash;

        private CacheIndex(AlgorithmIdentifier algId, byte[] chainHash)
        {
            this.algId = algId;
            this.chainHash = chainHash;
        }

        public boolean equals(Object o)
        {
            if (this == o)
            {
                return true;
            }
            if (!(o instanceof CacheIndex))
            {
                return false;
            }
            CacheIndex that = (CacheIndex)o;
            return algId.equals(that.algId) && Arrays.areEqual(chainHash, that.chainHash);
        }

        public int hashCode()
        {
            int result = algId.hashCode();
            return 31 * result + Arrays.hashCode(chainHash);
        }
    }
}