package org.bouncycastle.crypto.digests;


/**
 * Draft FIPS 180-2 implementation of SHA-512. <b>Note:</b> As this is
 * based on a draft this implementation is subject to change.
 *
 * <pre>
 *         block  word  digest
 * SHA-1   512    32    160
 * SHA-256 512    32    256
 * SHA-384 1024   64    384
 * SHA-512 1024   64    512
 * </pre>
 */
public class SHA512Digest
    extends LongDigest
{
    private static final int    DIGEST_LENGTH = 64;

	/**
	 * Standard constructor
	 */
    public SHA512Digest()
    {
    }

	/**
	 * Copy constructor.  This will copy the state of the provided
	 * message digest.
	 */
	public SHA512Digest(SHA512Digest t)
	{
		super(t);
	}

    public String getAlgorithmName()
    {
        return "SHA-512";
    }

    public int getDigestSize()
    {
        return DIGEST_LENGTH;
    }

    public int doFinal(
        byte[]  out,
        int     outOff)
    {
        finish();

        unpackWord(H1, out, outOff);
        unpackWord(H2, out, outOff + 8);
        unpackWord(H3, out, outOff + 16);
        unpackWord(H4, out, outOff + 24);
        unpackWord(H5, out, outOff + 32);
        unpackWord(H6, out, outOff + 40);
        unpackWord(H7, out, outOff + 48);
        unpackWord(H8, out, outOff + 56);

        reset();

        return DIGEST_LENGTH;
    }

    /**
     * reset the chaining variables
     */
    public void reset()
    {
        super.reset();

		/* SHA-512 initial hash value
		 * The first 64 bits of the fractional parts of the square roots
		 * of the first eight prime numbers
		 */
		H1 = 0x6a09e667f3bcc908l;
		H2 = 0xbb67ae8584caa73bl;
		H3 = 0x3c6ef372fe94f82bl;
		H4 = 0xa54ff53a5f1d36f1l;
		H5 = 0x510e527fade682d1l;
		H6 = 0x9b05688c2b3e6c1fl;
		H7 = 0x1f83d9abfb41bd6bl;
		H8 = 0x5be0cd19137e2179L;
    }
}