/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

/*
 * This package is based on the work done by Keiron Liddle), Aftex Software
 * <keiron@aftexsw.com> to whom the Ant project is very grateful for his
 * great code.
 */

using System.Diagnostics;

namespace Org.BouncyCastle.Utilities.Bzip2
{
    /**
    * A simple class the hold and calculate the CRC for sanity checking
    * of the data.
    *
    * @author <a href="mailto:keiron@aftexsw.com">Keiron Liddle</a>
    */
    internal class CRC
    {
        // Values are byte-reversed
        private static readonly uint[] Crc32Table = {
            0x00000000, 0xB71DC104, 0x6E3B8209, 0xD926430D,
            0xDC760413, 0x6B6BC517, 0xB24D861A, 0x0550471E,
            0xB8ED0826, 0x0FF0C922, 0xD6D68A2F, 0x61CB4B2B,
            0x649B0C35, 0xD386CD31, 0x0AA08E3C, 0xBDBD4F38,
            0x70DB114C, 0xC7C6D048, 0x1EE09345, 0xA9FD5241,
            0xACAD155F, 0x1BB0D45B, 0xC2969756, 0x758B5652,
            0xC836196A, 0x7F2BD86E, 0xA60D9B63, 0x11105A67,
            0x14401D79, 0xA35DDC7D, 0x7A7B9F70, 0xCD665E74,
            0xE0B62398, 0x57ABE29C, 0x8E8DA191, 0x39906095,
            0x3CC0278B, 0x8BDDE68F, 0x52FBA582, 0xE5E66486,
            0x585B2BBE, 0xEF46EABA, 0x3660A9B7, 0x817D68B3,
            0x842D2FAD, 0x3330EEA9, 0xEA16ADA4, 0x5D0B6CA0,
            0x906D32D4, 0x2770F3D0, 0xFE56B0DD, 0x494B71D9,
            0x4C1B36C7, 0xFB06F7C3, 0x2220B4CE, 0x953D75CA,
            0x28803AF2, 0x9F9DFBF6, 0x46BBB8FB, 0xF1A679FF,
            0xF4F63EE1, 0x43EBFFE5, 0x9ACDBCE8, 0x2DD07DEC,
            0x77708634, 0xC06D4730, 0x194B043D, 0xAE56C539,
            0xAB068227, 0x1C1B4323, 0xC53D002E, 0x7220C12A,
            0xCF9D8E12, 0x78804F16, 0xA1A60C1B, 0x16BBCD1F,
            0x13EB8A01, 0xA4F64B05, 0x7DD00808, 0xCACDC90C,
            0x07AB9778, 0xB0B6567C, 0x69901571, 0xDE8DD475,
            0xDBDD936B, 0x6CC0526F, 0xB5E61162, 0x02FBD066,
            0xBF469F5E, 0x085B5E5A, 0xD17D1D57, 0x6660DC53,
            0x63309B4D, 0xD42D5A49, 0x0D0B1944, 0xBA16D840,
            0x97C6A5AC, 0x20DB64A8, 0xF9FD27A5, 0x4EE0E6A1,
            0x4BB0A1BF, 0xFCAD60BB, 0x258B23B6, 0x9296E2B2,
            0x2F2BAD8A, 0x98366C8E, 0x41102F83, 0xF60DEE87,
            0xF35DA999, 0x4440689D, 0x9D662B90, 0x2A7BEA94,
            0xE71DB4E0, 0x500075E4, 0x892636E9, 0x3E3BF7ED,
            0x3B6BB0F3, 0x8C7671F7, 0x555032FA, 0xE24DF3FE,
            0x5FF0BCC6, 0xE8ED7DC2, 0x31CB3ECF, 0x86D6FFCB,
            0x8386B8D5, 0x349B79D1, 0xEDBD3ADC, 0x5AA0FBD8,
            0xEEE00C69, 0x59FDCD6D, 0x80DB8E60, 0x37C64F64,
            0x3296087A, 0x858BC97E, 0x5CAD8A73, 0xEBB04B77,
            0x560D044F, 0xE110C54B, 0x38368646, 0x8F2B4742,
            0x8A7B005C, 0x3D66C158, 0xE4408255, 0x535D4351,
            0x9E3B1D25, 0x2926DC21, 0xF0009F2C, 0x471D5E28,
            0x424D1936, 0xF550D832, 0x2C769B3F, 0x9B6B5A3B,
            0x26D61503, 0x91CBD407, 0x48ED970A, 0xFFF0560E,
            0xFAA01110, 0x4DBDD014, 0x949B9319, 0x2386521D,
            0x0E562FF1, 0xB94BEEF5, 0x606DADF8, 0xD7706CFC,
            0xD2202BE2, 0x653DEAE6, 0xBC1BA9EB, 0x0B0668EF,
            0xB6BB27D7, 0x01A6E6D3, 0xD880A5DE, 0x6F9D64DA,
            0x6ACD23C4, 0xDDD0E2C0, 0x04F6A1CD, 0xB3EB60C9,
            0x7E8D3EBD, 0xC990FFB9, 0x10B6BCB4, 0xA7AB7DB0,
            0xA2FB3AAE, 0x15E6FBAA, 0xCCC0B8A7, 0x7BDD79A3,
            0xC660369B, 0x717DF79F, 0xA85BB492, 0x1F467596,
            0x1A163288, 0xAD0BF38C, 0x742DB081, 0xC3307185,
            0x99908A5D, 0x2E8D4B59, 0xF7AB0854, 0x40B6C950,
            0x45E68E4E, 0xF2FB4F4A, 0x2BDD0C47, 0x9CC0CD43,
            0x217D827B, 0x9660437F, 0x4F460072, 0xF85BC176,
            0xFD0B8668, 0x4A16476C, 0x93300461, 0x242DC565,
            0xE94B9B11, 0x5E565A15, 0x87701918, 0x306DD81C,
            0x353D9F02, 0x82205E06, 0x5B061D0B, 0xEC1BDC0F,
            0x51A69337, 0xE6BB5233, 0x3F9D113E, 0x8880D03A,
            0x8DD09724, 0x3ACD5620, 0xE3EB152D, 0x54F6D429,
            0x7926A9C5, 0xCE3B68C1, 0x171D2BCC, 0xA000EAC8,
            0xA550ADD6, 0x124D6CD2, 0xCB6B2FDF, 0x7C76EEDB,
            0xC1CBA1E3, 0x76D660E7, 0xAFF023EA, 0x18EDE2EE,
            0x1DBDA5F0, 0xAAA064F4, 0x738627F9, 0xC49BE6FD,
            0x09FDB889, 0xBEE0798D, 0x67C63A80, 0xD0DBFB84,
            0xD58BBC9A, 0x62967D9E, 0xBBB03E93, 0x0CADFF97,
            0xB110B0AF, 0x060D71AB, 0xDF2B32A6, 0x6836F3A2,
            0x6D66B4BC, 0xDA7B75B8, 0x035D36B5, 0xB440F7B1,
        };

        private uint m_value = 0U;

        internal void Initialise()
        {
            m_value = 0xFFFFFFFF;
        }

        internal int GetFinal()
        {
            return (int)~Integers.ReverseBytes(m_value);
        }

        internal void Update(byte inCh)
        {
            m_value = (m_value >> 8) ^ Crc32Table[(byte)(m_value ^ inCh)];
        }

        internal void UpdateRun(byte inCh, int runLength)
        {
            Debug.Assert(runLength >= 4);

            uint inCh2 = (uint)inCh << 8 | inCh;
            uint inCh4 = inCh2 << 16 | inCh2;

            do
            {
                m_value ^= inCh4;
                m_value = (m_value >> 8) ^ Crc32Table[(byte)m_value];
                m_value = (m_value >> 8) ^ Crc32Table[(byte)m_value];
                m_value = (m_value >> 8) ^ Crc32Table[(byte)m_value];
                m_value = (m_value >> 8) ^ Crc32Table[(byte)m_value];
            }
            while ((runLength -= 4) >= 4);

            switch (runLength & 3)
            {
            case 0:
                break;
            case 1:
                Update(inCh);
                break;
            case 2:
                Update(inCh);
                Update(inCh);
                break;
            case 3:
                Update(inCh);
                Update(inCh);
                Update(inCh);
                break;
            }
        }
    }
}