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/*
 * Copyright 2014 The Netty Project
 *
 * The Netty Project 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:
 *
 *   https://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.
 */
package io.netty.handler.codec.compression;

/**
 * A CRC32 calculator.
 */
final class Crc32 {
    /**
     * A static CRC lookup table.
     */
    private static final int[] crc32Table = {
            0x00000000, 0x04c11db7, 0x09823b6e, 0x0d4326d9,
            0x130476dc, 0x17c56b6b, 0x1a864db2, 0x1e475005,
            0x2608edb8, 0x22c9f00f, 0x2f8ad6d6, 0x2b4bcb61,
            0x350c9b64, 0x31cd86d3, 0x3c8ea00a, 0x384fbdbd,
            0x4c11db70, 0x48d0c6c7, 0x4593e01e, 0x4152fda9,
            0x5f15adac, 0x5bd4b01b, 0x569796c2, 0x52568b75,
            0x6a1936c8, 0x6ed82b7f, 0x639b0da6, 0x675a1011,
            0x791d4014, 0x7ddc5da3, 0x709f7b7a, 0x745e66cd,
            0x9823b6e0, 0x9ce2ab57, 0x91a18d8e, 0x95609039,
            0x8b27c03c, 0x8fe6dd8b, 0x82a5fb52, 0x8664e6e5,
            0xbe2b5b58, 0xbaea46ef, 0xb7a96036, 0xb3687d81,
            0xad2f2d84, 0xa9ee3033, 0xa4ad16ea, 0xa06c0b5d,
            0xd4326d90, 0xd0f37027, 0xddb056fe, 0xd9714b49,
            0xc7361b4c, 0xc3f706fb, 0xceb42022, 0xca753d95,
            0xf23a8028, 0xf6fb9d9f, 0xfbb8bb46, 0xff79a6f1,
            0xe13ef6f4, 0xe5ffeb43, 0xe8bccd9a, 0xec7dd02d,
            0x34867077, 0x30476dc0, 0x3d044b19, 0x39c556ae,
            0x278206ab, 0x23431b1c, 0x2e003dc5, 0x2ac12072,
            0x128e9dcf, 0x164f8078, 0x1b0ca6a1, 0x1fcdbb16,
            0x018aeb13, 0x054bf6a4, 0x0808d07d, 0x0cc9cdca,
            0x7897ab07, 0x7c56b6b0, 0x71159069, 0x75d48dde,
            0x6b93dddb, 0x6f52c06c, 0x6211e6b5, 0x66d0fb02,
            0x5e9f46bf, 0x5a5e5b08, 0x571d7dd1, 0x53dc6066,
            0x4d9b3063, 0x495a2dd4, 0x44190b0d, 0x40d816ba,
            0xaca5c697, 0xa864db20, 0xa527fdf9, 0xa1e6e04e,
            0xbfa1b04b, 0xbb60adfc, 0xb6238b25, 0xb2e29692,
            0x8aad2b2f, 0x8e6c3698, 0x832f1041, 0x87ee0df6,
            0x99a95df3, 0x9d684044, 0x902b669d, 0x94ea7b2a,
            0xe0b41de7, 0xe4750050, 0xe9362689, 0xedf73b3e,
            0xf3b06b3b, 0xf771768c, 0xfa325055, 0xfef34de2,
            0xc6bcf05f, 0xc27dede8, 0xcf3ecb31, 0xcbffd686,
            0xd5b88683, 0xd1799b34, 0xdc3abded, 0xd8fba05a,
            0x690ce0ee, 0x6dcdfd59, 0x608edb80, 0x644fc637,
            0x7a089632, 0x7ec98b85, 0x738aad5c, 0x774bb0eb,
            0x4f040d56, 0x4bc510e1, 0x46863638, 0x42472b8f,
            0x5c007b8a, 0x58c1663d, 0x558240e4, 0x51435d53,
            0x251d3b9e, 0x21dc2629, 0x2c9f00f0, 0x285e1d47,
            0x36194d42, 0x32d850f5, 0x3f9b762c, 0x3b5a6b9b,
            0x0315d626, 0x07d4cb91, 0x0a97ed48, 0x0e56f0ff,
            0x1011a0fa, 0x14d0bd4d, 0x19939b94, 0x1d528623,
            0xf12f560e, 0xf5ee4bb9, 0xf8ad6d60, 0xfc6c70d7,
            0xe22b20d2, 0xe6ea3d65, 0xeba91bbc, 0xef68060b,
            0xd727bbb6, 0xd3e6a601, 0xdea580d8, 0xda649d6f,
            0xc423cd6a, 0xc0e2d0dd, 0xcda1f604, 0xc960ebb3,
            0xbd3e8d7e, 0xb9ff90c9, 0xb4bcb610, 0xb07daba7,
            0xae3afba2, 0xaafbe615, 0xa7b8c0cc, 0xa379dd7b,
            0x9b3660c6, 0x9ff77d71, 0x92b45ba8, 0x9675461f,
            0x8832161a, 0x8cf30bad, 0x81b02d74, 0x857130c3,
            0x5d8a9099, 0x594b8d2e, 0x5408abf7, 0x50c9b640,
            0x4e8ee645, 0x4a4ffbf2, 0x470cdd2b, 0x43cdc09c,
            0x7b827d21, 0x7f436096, 0x7200464f, 0x76c15bf8,
            0x68860bfd, 0x6c47164a, 0x61043093, 0x65c52d24,
            0x119b4be9, 0x155a565e, 0x18197087, 0x1cd86d30,
            0x029f3d35, 0x065e2082, 0x0b1d065b, 0x0fdc1bec,
            0x3793a651, 0x3352bbe6, 0x3e119d3f, 0x3ad08088,
            0x2497d08d, 0x2056cd3a, 0x2d15ebe3, 0x29d4f654,
            0xc5a92679, 0xc1683bce, 0xcc2b1d17, 0xc8ea00a0,
            0xd6ad50a5, 0xd26c4d12, 0xdf2f6bcb, 0xdbee767c,
            0xe3a1cbc1, 0xe760d676, 0xea23f0af, 0xeee2ed18,
            0xf0a5bd1d, 0xf464a0aa, 0xf9278673, 0xfde69bc4,
            0x89b8fd09, 0x8d79e0be, 0x803ac667, 0x84fbdbd0,
            0x9abc8bd5, 0x9e7d9662, 0x933eb0bb, 0x97ffad0c,
            0xafb010b1, 0xab710d06, 0xa6322bdf, 0xa2f33668,
            0xbcb4666d, 0xb8757bda, 0xb5365d03, 0xb1f740b4
    };

    /**
     * The current CRC.
     */
    private int crc = 0xffffffff;

    /**
     * @return The current CRC.
     */
    public int getCRC() {
        return ~crc;
    }

    /**
     * Update the CRC with a single byte.
     * @param value The value to update the CRC with
     */
    public void updateCRC(final int value) {
        final int crc = this.crc;
        this.crc = crc << 8 ^ crc32Table[(crc >> 24 ^ value) & 0xff];
    }

    /**
     * Update the CRC with a sequence of identical bytes.
     * @param value The value to update the CRC with
     * @param count The number of bytes
     */
    public void updateCRC(final int value, int count) {
        while (count-- > 0) {
            updateCRC(value);
        }
    }
}