/*
    * Copyright (C) 2017, Google Inc.
    * and other copyright owners as documented in the project's IP log.
    *
    * This program and the accompanying materials are made available
    * under the terms of the Eclipse Distribution License v1.0 which
    * accompanies this distribution, is reproduced below, and is
    * available at http://www.eclipse.org/org/documents/edl-v10.php
    *
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or
   * without modification, are permitted provided that the following
   * conditions are met:
   *
   * - Redistributions of source code must retain the above copyright
   *   notice, this list of conditions and the following disclaimer.
   *
   * - Redistributions in binary form must reproduce the above
   *   copyright notice, this list of conditions and the following
   *   disclaimer in the documentation and/or other materials provided
   *   with the distribution.
   *
   * - Neither the name of the Eclipse Foundation, Inc. nor the
   *   names of its contributors may be used to endorse or promote
   *   products derived from this software without specific prior
   *   written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
   * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
   * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
   * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
   * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  
  package org.eclipse.jgit.util.sha1;
  
  import static java.lang.Integer.lowestOneBit;
  import static java.lang.Integer.numberOfTrailingZeros;
  import static java.lang.Integer.rotateLeft;
  import static java.lang.Integer.rotateRight;
  
  import java.util.Arrays;
  
  import org.eclipse.jgit.lib.MutableObjectId;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.util.NB;
  import org.eclipse.jgit.util.SystemReader;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * Pure Java implementation of SHA-1 from FIPS 180-1 / RFC 3174.
   *
   * <p>
   * See <a href="https://tools.ietf.org/html/rfc3174">RFC 3174</a>.
   * <p>
   * Unlike MessageDigest, this implementation includes the algorithm used by
   * {@code sha1dc} to detect cryptanalytic collision attacks against SHA-1, such
   * as the one used by <a href="https://shattered.it/">SHAttered</a>. See
   * <a href="https://github.com/cr-marcstevens/sha1collisiondetection">
   * sha1collisiondetection</a> for more information.
   * <p>
   * When detectCollision is true (default), this implementation throws
   * {@link Sha1CollisionException} from any digest method if a potential
   * collision was detected.
   *
   * @since 4.7
   */
  public class SHA1 {
  	private static Logger LOG = LoggerFactory.getLogger(SHA1.class);
  	private static final boolean DETECT_COLLISIONS;
  
  	static {
  		SystemReader sr = SystemReader.getInstance();
  		String v = sr.getProperty("org.eclipse.jgit.util.sha1.detectCollision"); //$NON-NLS-1$
  		DETECT_COLLISIONS = v != null ? Boolean.parseBoolean(v) : true;
  	}
  
  	/** @return a new context to compute a SHA-1 hash of data. */
  	public static SHA1 newInstance() {
  		return new SHA1();
  	}
  
  	private final State h = new State();
  	private final int[] w = new int[80];
  
  	/** Buffer to accumulate partial blocks to 64 byte alignment. */
  	private final byte[] buffer = new byte[64];
  
  	/** Total number of bytes in the message. */
 	private long length;
 
 	private boolean detectCollision = DETECT_COLLISIONS;
 	private boolean foundCollision;
 
 	private final int[] w2 = new int[80];
 	private final State state58 = new State();
 	private final State state65 = new State();
 	private final State hIn = new State();
 	private final State hTmp = new State();
 
 	private SHA1() {
 		h.init();
 	}
 
 	/**
 	 * Enable likely collision detection.
 	 * <p>
 	 * Default is {@code true}.
 	 * <p>
 	 * May also be set by system property:
 	 * {@code -Dorg.eclipse.jgit.util.sha1.detectCollision=true}.
 	 *
 	 * @param detect
 	 * @return {@code this}
 	 */
 	public SHA1 setDetectCollision(boolean detect) {
 		detectCollision = detect;
 		return this;
 	}
 
 	/**
 	 * Update the digest computation by adding a byte.
 	 *
 	 * @param b
 	 */
 	public void update(byte b) {
 		int bufferLen = (int) (length & 63);
 		length++;
 		buffer[bufferLen] = b;
 		if (bufferLen == 63) {
 			compress(buffer, 0);
 		}
 	}
 
 	/**
 	 * Update the digest computation by adding bytes to the message.
 	 *
 	 * @param in
 	 *            input array of bytes.
 	 */
 	public void update(byte[] in) {
 		update(in, 0, in.length);
 	}
 
 	/**
 	 * Update the digest computation by adding bytes to the message.
 	 *
 	 * @param in
 	 *            input array of bytes.
 	 * @param p
 	 *            offset to start at from {@code in}.
 	 * @param len
 	 *            number of bytes to hash.
 	 */
 	public void update(byte[] in, int p, int len) {
 		// SHA-1 compress can only process whole 64 byte blocks.
 		// Hold partial updates in buffer, whose length is the low bits.
 		int bufferLen = (int) (length & 63);
 		length += len;
 
 		if (bufferLen > 0) {
 			int n = Math.min(64 - bufferLen, len);
 			System.arraycopy(in, p, buffer, bufferLen, n);
 			p += n;
 			len -= n;
 			if (bufferLen + n < 64) {
 				return;
 			}
 			compress(buffer, 0);
 		}
 		while (len >= 64) {
 			compress(in, p);
 			p += 64;
 			len -= 64;
 		}
 		if (len > 0) {
 			System.arraycopy(in, p, buffer, 0, len);
 		}
 	}
 
 	private void compress(byte[] block, int p) {
 		initBlock(block, p);
 		int ubcDvMask = detectCollision ? UbcCheck.check(w) : 0;
 		compress();
 
 		while (ubcDvMask != 0) {
 			int b = numberOfTrailingZeros(lowestOneBit(ubcDvMask));
 			UbcCheck.DvInfo dv = UbcCheck.DV[b];
 			for (int i = 0; i < 80; i++) {
 				w2[i] = w[i] ^ dv.dm[i];
 			}
 			recompress(dv.testt);
 			if (eq(hTmp, h)) {
 				foundCollision = true;
 				break;
 			}
 			ubcDvMask &= ~(1 << b);
 		}
 	}
 
 	private void initBlock(byte[] block, int p) {
 		for (int t = 0; t < 16; t++) {
 			w[t] = NB.decodeInt32(block, p + (t << 2));
 		}
 
 		// RFC 3174 6.1.b, extend state vector to 80 words.
 		for (int t = 16; t < 80; t++) {
 			int x = w[t - 3] ^ w[t - 8] ^ w[t - 14] ^ w[t - 16];
 			w[t] = rotateLeft(x, 1); // S^1(...)
 		}
 	}
 
 	private void compress() {
 		// Method 1 from RFC 3174 section 6.1.
 		// Method 2 (circular queue of 16 words) is slower.
 		int a = h.a, b = h.b, c = h.c, d = h.d, e = h.e;
 
 		// @formatter:off
 		 e += s1(a, b, c, d,w[ 0]);  b = rotateLeft( b, 30);
 		 d += s1(e, a, b, c,w[ 1]);  a = rotateLeft( a, 30);
 		 c += s1(d, e, a, b,w[ 2]);  e = rotateLeft( e, 30);
 		 b += s1(c, d, e, a,w[ 3]);  d = rotateLeft( d, 30);
 		 a += s1(b, c, d, e,w[ 4]);  c = rotateLeft( c, 30);
 		 e += s1(a, b, c, d,w[ 5]);  b = rotateLeft( b, 30);
 		 d += s1(e, a, b, c,w[ 6]);  a = rotateLeft( a, 30);
 		 c += s1(d, e, a, b,w[ 7]);  e = rotateLeft( e, 30);
 		 b += s1(c, d, e, a,w[ 8]);  d = rotateLeft( d, 30);
 		 a += s1(b, c, d, e,w[ 9]);  c = rotateLeft( c, 30);
 		 e += s1(a, b, c, d,w[ 10]);  b = rotateLeft( b, 30);
 		 d += s1(e, a, b, c,w[ 11]);  a = rotateLeft( a, 30);
 		 c += s1(d, e, a, b,w[ 12]);  e = rotateLeft( e, 30);
 		 b += s1(c, d, e, a,w[ 13]);  d = rotateLeft( d, 30);
 		 a += s1(b, c, d, e,w[ 14]);  c = rotateLeft( c, 30);
 		 e += s1(a, b, c, d,w[ 15]);  b = rotateLeft( b, 30);
 		 d += s1(e, a, b, c,w[ 16]);  a = rotateLeft( a, 30);
 		 c += s1(d, e, a, b,w[ 17]);  e = rotateLeft( e, 30);
 		 b += s1(c, d, e, a,w[ 18]);  d = rotateLeft( d, 30);
 		 a += s1(b, c, d, e,w[ 19]);  c = rotateLeft( c, 30);
 
 		 e += s2(a, b, c, d,w[ 20]);  b = rotateLeft( b, 30);
 		 d += s2(e, a, b, c,w[ 21]);  a = rotateLeft( a, 30);
 		 c += s2(d, e, a, b,w[ 22]);  e = rotateLeft( e, 30);
 		 b += s2(c, d, e, a,w[ 23]);  d = rotateLeft( d, 30);
 		 a += s2(b, c, d, e,w[ 24]);  c = rotateLeft( c, 30);
 		 e += s2(a, b, c, d,w[ 25]);  b = rotateLeft( b, 30);
 		 d += s2(e, a, b, c,w[ 26]);  a = rotateLeft( a, 30);
 		 c += s2(d, e, a, b,w[ 27]);  e = rotateLeft( e, 30);
 		 b += s2(c, d, e, a,w[ 28]);  d = rotateLeft( d, 30);
 		 a += s2(b, c, d, e,w[ 29]);  c = rotateLeft( c, 30);
 		 e += s2(a, b, c, d,w[ 30]);  b = rotateLeft( b, 30);
 		 d += s2(e, a, b, c,w[ 31]);  a = rotateLeft( a, 30);
 		 c += s2(d, e, a, b,w[ 32]);  e = rotateLeft( e, 30);
 		 b += s2(c, d, e, a,w[ 33]);  d = rotateLeft( d, 30);
 		 a += s2(b, c, d, e,w[ 34]);  c = rotateLeft( c, 30);
 		 e += s2(a, b, c, d,w[ 35]);  b = rotateLeft( b, 30);
 		 d += s2(e, a, b, c,w[ 36]);  a = rotateLeft( a, 30);
 		 c += s2(d, e, a, b,w[ 37]);  e = rotateLeft( e, 30);
 		 b += s2(c, d, e, a,w[ 38]);  d = rotateLeft( d, 30);
 		 a += s2(b, c, d, e,w[ 39]);  c = rotateLeft( c, 30);
 
 		 e += s3(a, b, c, d,w[ 40]);  b = rotateLeft( b, 30);
 		 d += s3(e, a, b, c,w[ 41]);  a = rotateLeft( a, 30);
 		 c += s3(d, e, a, b,w[ 42]);  e = rotateLeft( e, 30);
 		 b += s3(c, d, e, a,w[ 43]);  d = rotateLeft( d, 30);
 		 a += s3(b, c, d, e,w[ 44]);  c = rotateLeft( c, 30);
 		 e += s3(a, b, c, d,w[ 45]);  b = rotateLeft( b, 30);
 		 d += s3(e, a, b, c,w[ 46]);  a = rotateLeft( a, 30);
 		 c += s3(d, e, a, b,w[ 47]);  e = rotateLeft( e, 30);
 		 b += s3(c, d, e, a,w[ 48]);  d = rotateLeft( d, 30);
 		 a += s3(b, c, d, e,w[ 49]);  c = rotateLeft( c, 30);
 		 e += s3(a, b, c, d,w[ 50]);  b = rotateLeft( b, 30);
 		 d += s3(e, a, b, c,w[ 51]);  a = rotateLeft( a, 30);
 		 c += s3(d, e, a, b,w[ 52]);  e = rotateLeft( e, 30);
 		 b += s3(c, d, e, a,w[ 53]);  d = rotateLeft( d, 30);
 		 a += s3(b, c, d, e,w[ 54]);  c = rotateLeft( c, 30);
 		 e += s3(a, b, c, d,w[ 55]);  b = rotateLeft( b, 30);
 		 d += s3(e, a, b, c,w[ 56]);  a = rotateLeft( a, 30);
 		 c += s3(d, e, a, b,w[ 57]);  e = rotateLeft( e, 30);
 		state58.save(a, b, c, d, e);
 		 b += s3(c, d, e, a,w[ 58]);  d = rotateLeft( d, 30);
 		 a += s3(b, c, d, e,w[ 59]);  c = rotateLeft( c, 30);
 
 		 e += s4(a, b, c, d,w[ 60]);  b = rotateLeft( b, 30);
 		 d += s4(e, a, b, c,w[ 61]);  a = rotateLeft( a, 30);
 		 c += s4(d, e, a, b,w[ 62]);  e = rotateLeft( e, 30);
 		 b += s4(c, d, e, a,w[ 63]);  d = rotateLeft( d, 30);
 		 a += s4(b, c, d, e,w[ 64]);  c = rotateLeft( c, 30);
 		state65.save(a, b, c, d, e);
 		 e += s4(a, b, c, d,w[ 65]);  b = rotateLeft( b, 30);
 		 d += s4(e, a, b, c,w[ 66]);  a = rotateLeft( a, 30);
 		 c += s4(d, e, a, b,w[ 67]);  e = rotateLeft( e, 30);
 		 b += s4(c, d, e, a,w[ 68]);  d = rotateLeft( d, 30);
 		 a += s4(b, c, d, e,w[ 69]);  c = rotateLeft( c, 30);
 		 e += s4(a, b, c, d,w[ 70]);  b = rotateLeft( b, 30);
 		 d += s4(e, a, b, c,w[ 71]);  a = rotateLeft( a, 30);
 		 c += s4(d, e, a, b,w[ 72]);  e = rotateLeft( e, 30);
 		 b += s4(c, d, e, a,w[ 73]);  d = rotateLeft( d, 30);
 		 a += s4(b, c, d, e,w[ 74]);  c = rotateLeft( c, 30);
 		 e += s4(a, b, c, d,w[ 75]);  b = rotateLeft( b, 30);
 		 d += s4(e, a, b, c,w[ 76]);  a = rotateLeft( a, 30);
 		 c += s4(d, e, a, b,w[ 77]);  e = rotateLeft( e, 30);
 		 b += s4(c, d, e, a,w[ 78]);  d = rotateLeft( d, 30);
 		 a += s4(b, c, d, e,w[ 79]);  c = rotateLeft( c, 30);
 
 		// @formatter:on
 		h.save(h.a + a, h.b + b, h.c + c, h.d + d, h.e + e);
 	}
 
 	private void recompress(int t) {
 		State s;
 		if (t == 58) {
 			s = state58;
 		} else if (t == 65) {
 			s = state65;
 		} else {
 			throw new IllegalStateException();
 		}
 		int a = s.a, b = s.b, c = s.c, d = s.d, e = s.e;
 
 		// @formatter:off
 	  if (t == 65) {
 		{ c = rotateRight( c, 30);  a -= s4(b, c, d, e,w2[ 64]);}
 		{ d = rotateRight( d, 30);  b -= s4(c, d, e, a,w2[ 63]);}
 		{ e = rotateRight( e, 30);  c -= s4(d, e, a, b,w2[ 62]);}
 		{ a = rotateRight( a, 30);  d -= s4(e, a, b, c,w2[ 61]);}
 		{ b = rotateRight( b, 30);  e -= s4(a, b, c, d,w2[ 60]);}
 
 		{ c = rotateRight( c, 30);  a -= s3(b, c, d, e,w2[ 59]);}
 		{ d = rotateRight( d, 30);  b -= s3(c, d, e, a,w2[ 58]);}
 	  }
 		{ e = rotateRight( e, 30);  c -= s3(d, e, a, b,w2[ 57]);}
 		{ a = rotateRight( a, 30);  d -= s3(e, a, b, c,w2[ 56]);}
 		{ b = rotateRight( b, 30);  e -= s3(a, b, c, d,w2[ 55]);}
 		{ c = rotateRight( c, 30);  a -= s3(b, c, d, e,w2[ 54]);}
 		{ d = rotateRight( d, 30);  b -= s3(c, d, e, a,w2[ 53]);}
 		{ e = rotateRight( e, 30);  c -= s3(d, e, a, b,w2[ 52]);}
 		{ a = rotateRight( a, 30);  d -= s3(e, a, b, c,w2[ 51]);}
 		{ b = rotateRight( b, 30);  e -= s3(a, b, c, d,w2[ 50]);}
 		{ c = rotateRight( c, 30);  a -= s3(b, c, d, e,w2[ 49]);}
 		{ d = rotateRight( d, 30);  b -= s3(c, d, e, a,w2[ 48]);}
 		{ e = rotateRight( e, 30);  c -= s3(d, e, a, b,w2[ 47]);}
 		{ a = rotateRight( a, 30);  d -= s3(e, a, b, c,w2[ 46]);}
 		{ b = rotateRight( b, 30);  e -= s3(a, b, c, d,w2[ 45]);}
 		{ c = rotateRight( c, 30);  a -= s3(b, c, d, e,w2[ 44]);}
 		{ d = rotateRight( d, 30);  b -= s3(c, d, e, a,w2[ 43]);}
 		{ e = rotateRight( e, 30);  c -= s3(d, e, a, b,w2[ 42]);}
 		{ a = rotateRight( a, 30);  d -= s3(e, a, b, c,w2[ 41]);}
 		{ b = rotateRight( b, 30);  e -= s3(a, b, c, d,w2[ 40]);}
 
 		{ c = rotateRight( c, 30);  a -= s2(b, c, d, e,w2[ 39]);}
 		{ d = rotateRight( d, 30);  b -= s2(c, d, e, a,w2[ 38]);}
 		{ e = rotateRight( e, 30);  c -= s2(d, e, a, b,w2[ 37]);}
 		{ a = rotateRight( a, 30);  d -= s2(e, a, b, c,w2[ 36]);}
 		{ b = rotateRight( b, 30);  e -= s2(a, b, c, d,w2[ 35]);}
 		{ c = rotateRight( c, 30);  a -= s2(b, c, d, e,w2[ 34]);}
 		{ d = rotateRight( d, 30);  b -= s2(c, d, e, a,w2[ 33]);}
 		{ e = rotateRight( e, 30);  c -= s2(d, e, a, b,w2[ 32]);}
 		{ a = rotateRight( a, 30);  d -= s2(e, a, b, c,w2[ 31]);}
 		{ b = rotateRight( b, 30);  e -= s2(a, b, c, d,w2[ 30]);}
 		{ c = rotateRight( c, 30);  a -= s2(b, c, d, e,w2[ 29]);}
 		{ d = rotateRight( d, 30);  b -= s2(c, d, e, a,w2[ 28]);}
 		{ e = rotateRight( e, 30);  c -= s2(d, e, a, b,w2[ 27]);}
 		{ a = rotateRight( a, 30);  d -= s2(e, a, b, c,w2[ 26]);}
 		{ b = rotateRight( b, 30);  e -= s2(a, b, c, d,w2[ 25]);}
 		{ c = rotateRight( c, 30);  a -= s2(b, c, d, e,w2[ 24]);}
 		{ d = rotateRight( d, 30);  b -= s2(c, d, e, a,w2[ 23]);}
 		{ e = rotateRight( e, 30);  c -= s2(d, e, a, b,w2[ 22]);}
 		{ a = rotateRight( a, 30);  d -= s2(e, a, b, c,w2[ 21]);}
 		{ b = rotateRight( b, 30);  e -= s2(a, b, c, d,w2[ 20]);}
 
 		{ c = rotateRight( c, 30);  a -= s1(b, c, d, e,w2[ 19]);}
 		{ d = rotateRight( d, 30);  b -= s1(c, d, e, a,w2[ 18]);}
 		{ e = rotateRight( e, 30);  c -= s1(d, e, a, b,w2[ 17]);}
 		{ a = rotateRight( a, 30);  d -= s1(e, a, b, c,w2[ 16]);}
 		{ b = rotateRight( b, 30);  e -= s1(a, b, c, d,w2[ 15]);}
 		{ c = rotateRight( c, 30);  a -= s1(b, c, d, e,w2[ 14]);}
 		{ d = rotateRight( d, 30);  b -= s1(c, d, e, a,w2[ 13]);}
 		{ e = rotateRight( e, 30);  c -= s1(d, e, a, b,w2[ 12]);}
 		{ a = rotateRight( a, 30);  d -= s1(e, a, b, c,w2[ 11]);}
 		{ b = rotateRight( b, 30);  e -= s1(a, b, c, d,w2[ 10]);}
 		{ c = rotateRight( c, 30);  a -= s1(b, c, d, e,w2[ 9]);}
 		{ d = rotateRight( d, 30);  b -= s1(c, d, e, a,w2[ 8]);}
 		{ e = rotateRight( e, 30);  c -= s1(d, e, a, b,w2[ 7]);}
 		{ a = rotateRight( a, 30);  d -= s1(e, a, b, c,w2[ 6]);}
 		{ b = rotateRight( b, 30);  e -= s1(a, b, c, d,w2[ 5]);}
 		{ c = rotateRight( c, 30);  a -= s1(b, c, d, e,w2[ 4]);}
 		{ d = rotateRight( d, 30);  b -= s1(c, d, e, a,w2[ 3]);}
 		{ e = rotateRight( e, 30);  c -= s1(d, e, a, b,w2[ 2]);}
 		{ a = rotateRight( a, 30);  d -= s1(e, a, b, c,w2[ 1]);}
 		{ b = rotateRight( b, 30);  e -= s1(a, b, c, d,w2[ 0]);}
 
 		hIn.save(a, b, c, d, e);
 		a = s.a; b = s.b; c = s.c; d = s.d; e = s.e;
 
 	  if (t == 58) {
 		{ b += s3(c, d, e, a,w2[ 58]);  d = rotateLeft( d, 30);}
 		{ a += s3(b, c, d, e,w2[ 59]);  c = rotateLeft( c, 30);}
 
 		{ e += s4(a, b, c, d,w2[ 60]);  b = rotateLeft( b, 30);}
 		{ d += s4(e, a, b, c,w2[ 61]);  a = rotateLeft( a, 30);}
 		{ c += s4(d, e, a, b,w2[ 62]);  e = rotateLeft( e, 30);}
 		{ b += s4(c, d, e, a,w2[ 63]);  d = rotateLeft( d, 30);}
 		{ a += s4(b, c, d, e,w2[ 64]);  c = rotateLeft( c, 30);}
 	  }
 		{ e += s4(a, b, c, d,w2[ 65]);  b = rotateLeft( b, 30);}
 		{ d += s4(e, a, b, c,w2[ 66]);  a = rotateLeft( a, 30);}
 		{ c += s4(d, e, a, b,w2[ 67]);  e = rotateLeft( e, 30);}
 		{ b += s4(c, d, e, a,w2[ 68]);  d = rotateLeft( d, 30);}
 		{ a += s4(b, c, d, e,w2[ 69]);  c = rotateLeft( c, 30);}
 		{ e += s4(a, b, c, d,w2[ 70]);  b = rotateLeft( b, 30);}
 		{ d += s4(e, a, b, c,w2[ 71]);  a = rotateLeft( a, 30);}
 		{ c += s4(d, e, a, b,w2[ 72]);  e = rotateLeft( e, 30);}
 		{ b += s4(c, d, e, a,w2[ 73]);  d = rotateLeft( d, 30);}
 		{ a += s4(b, c, d, e,w2[ 74]);  c = rotateLeft( c, 30);}
 		{ e += s4(a, b, c, d,w2[ 75]);  b = rotateLeft( b, 30);}
 		{ d += s4(e, a, b, c,w2[ 76]);  a = rotateLeft( a, 30);}
 		{ c += s4(d, e, a, b,w2[ 77]);  e = rotateLeft( e, 30);}
 		{ b += s4(c, d, e, a,w2[ 78]);  d = rotateLeft( d, 30);}
 		{ a += s4(b, c, d, e,w2[ 79]);  c = rotateLeft( c, 30);}
 
 		// @formatter:on
 		hTmp.save(hIn.a + a, hIn.b + b, hIn.c + c, hIn.d + d, hIn.e + e);
 	}
 
 	private static int s1(int a, int b, int c, int d, int w_t) {
 		return rotateLeft(a, 5)
 				// f: 0 <= t <= 19
 				+ ((b & c) | ((~b) & d))
 				+ 0x5A827999 + w_t;
 	}
 
 	private static int s2(int a, int b, int c, int d, int w_t) {
 		return rotateLeft(a, 5)
 				// f: 20 <= t <= 39
 				+ (b ^ c ^ d)
 				+ 0x6ED9EBA1 + w_t;
 	}
 
 	private static int s3(int a, int b, int c, int d, int w_t) {
 		return rotateLeft(a, 5)
 				// f: 40 <= t <= 59
 				+ ((b & c) | (b & d) | (c & d))
 				+ 0x8F1BBCDC + w_t;
 	}
 
 	private static int s4(int a, int b, int c, int d, int w_t) {
 		return rotateLeft(a, 5)
 				// f: 60 <= t <= 79
 				+ (b ^ c ^ d)
 				+ 0xCA62C1D6 + w_t;
 	}
 
 	private static boolean eq(State q, State r) {
 		return q.a == r.a
 				&& q.b == r.b
 				&& q.c == r.c
 				&& q.d == r.d
 				&& q.e == r.e;
 	}
 
 	private void finish() {
 		int bufferLen = (int) (length & 63);
 		if (bufferLen > 55) {
 			// Last block is too small; pad, compress, pad another block.
 			buffer[bufferLen++] = (byte) 0x80;
 			Arrays.fill(buffer, bufferLen, 64, (byte) 0);
 			compress(buffer, 0);
 			Arrays.fill(buffer, 0, 56, (byte) 0);
 		} else {
 			// Last block can hold padding and length.
 			buffer[bufferLen++] = (byte) 0x80;
 			Arrays.fill(buffer, bufferLen, 56, (byte) 0);
 		}
 
 		// SHA-1 appends the length of the message in bits after the
 		// padding block (above). Here length is in bytes. Multiply by
 		// 8 by shifting by 3 as part of storing the 64 bit byte length
 		// into the two words expected in the trailer.
 		NB.encodeInt32(buffer, 56, (int) (length >>> (32 - 3)));
 		NB.encodeInt32(buffer, 60, (int) (length << 3));
 		compress(buffer, 0);
 
 		if (foundCollision) {
 			ObjectId id = h.toObjectId();
 			LOG.warn("possible SHA-1 collision " + id.name()); //$NON-NLS-1$
 			throw new Sha1CollisionException(id);
 		}
 	}
 
 	/**
 	 * Finish the digest and return the resulting hash.
 	 * <p>
 	 * Once {@code digest()} is called, this instance should be discarded.
 	 *
 	 * @return the bytes for the resulting hash.
 	 * @throws Sha1CollisionException
 	 *             if a collision was detected and safeHash is false.
 	 */
 	public byte[] digest() throws Sha1CollisionException {
 		finish();
 
 		byte[] b = new byte[20];
 		NB.encodeInt32(b, 0, h.a);
 		NB.encodeInt32(b, 4, h.b);
 		NB.encodeInt32(b, 8, h.c);
 		NB.encodeInt32(b, 12, h.d);
 		NB.encodeInt32(b, 16, h.e);
 		return b;
 	}
 
 	/**
 	 * Finish the digest and return the resulting hash.
 	 * <p>
 	 * Once {@code digest()} is called, this instance should be discarded.
 	 *
 	 * @return the ObjectId for the resulting hash.
 	 * @throws Sha1CollisionException
 	 *             if a collision was detected and safeHash is false.
 	 */
 	public ObjectId toObjectId() throws Sha1CollisionException {
 		finish();
 		return h.toObjectId();
 	}
 
 	/**
 	 * Finish the digest and return the resulting hash.
 	 * <p>
 	 * Once {@code digest()} is called, this instance should be discarded.
 	 *
 	 * @param id
 	 *            destination to copy the digest to.
 	 * @throws Sha1CollisionException
 	 *             if a collision was detected and safeHash is false.
 	 */
 	public void digest(MutableObjectId id) throws Sha1CollisionException {
 		finish();
 		id.set(h.a, h.b, h.c, h.d, h.e);
 	}
 
 	/**
 	 * Check if a collision was detected.
 	 *
 	 * <p>
 	 * This method only returns an accurate result after the digest was obtained
 	 * through {@link #digest()}, {@link #digest(MutableObjectId)} or
 	 * {@link #toObjectId()}, as the hashing function must finish processing to
 	 * know the final state.
 	 *
 	 * @return {@code true} if a likely collision was detected.
 	 */
 	public boolean hasCollision() {
 		return foundCollision;
 	}
 
 	/**
 	 * Reset this instance to compute another hash.
 	 *
 	 * @return {@code this}.
 	 */
 	public SHA1 reset() {
 		h.init();
 		length = 0;
 		foundCollision = false;
 		return this;
 	}
 
 	private static final class State {
 		int a;
 		int b;
 		int c;
 		int d;
 		int e;
 
 		final void init() {
 			// Magic initialization constants defined by FIPS180.
 			save(0x67452301, 0xEFCDAB89, 0x98BADCFE, 0x10325476, 0xC3D2E1F0);
 		}
 
 		final void save(int a1, int b1, int c1, int d1, int e1) {
 			a = a1;
 			b = b1;
 			c = c1;
 			d = d1;
 			e = e1;
 		}
 
 		ObjectId toObjectId() {
 			return new ObjectId(a, b, c, d, e);
 		}
 	}
 }