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Java example source code file (Crc32c.java)

This example Java source code file (Crc32c.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

byte_mask, checksum, crc32c, crc_table, long_mask, override, zip

The Crc32c.java Java example source code

/*
 * Copyright 2013 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:
 *
 *   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.
 */
package io.netty.handler.codec.compression;

import java.util.zip.Checksum;

/**
 * Implements CRC32-C as defined in:
 * "Optimization of Cyclic Redundancy-CHeck Codes with 24 and 32 Parity Bits",
 * IEEE Transactions on Communications 41(6): 883-892 (1993).
 *
 * The implementation of this class has been sourced from the Appendix of RFC 3309,
 * but with masking due to Java not being able to support unsigned types.
 */
class Crc32c implements Checksum {
    private static final int[] CRC_TABLE = {
            0x00000000, 0xF26B8303, 0xE13B70F7, 0x1350F3F4,
            0xC79A971F, 0x35F1141C, 0x26A1E7E8, 0xD4CA64EB,
            0x8AD958CF, 0x78B2DBCC, 0x6BE22838, 0x9989AB3B,
            0x4D43CFD0, 0xBF284CD3, 0xAC78BF27, 0x5E133C24,
            0x105EC76F, 0xE235446C, 0xF165B798, 0x030E349B,
            0xD7C45070, 0x25AFD373, 0x36FF2087, 0xC494A384,
            0x9A879FA0, 0x68EC1CA3, 0x7BBCEF57, 0x89D76C54,
            0x5D1D08BF, 0xAF768BBC, 0xBC267848, 0x4E4DFB4B,
            0x20BD8EDE, 0xD2D60DDD, 0xC186FE29, 0x33ED7D2A,
            0xE72719C1, 0x154C9AC2, 0x061C6936, 0xF477EA35,
            0xAA64D611, 0x580F5512, 0x4B5FA6E6, 0xB93425E5,
            0x6DFE410E, 0x9F95C20D, 0x8CC531F9, 0x7EAEB2FA,
            0x30E349B1, 0xC288CAB2, 0xD1D83946, 0x23B3BA45,
            0xF779DEAE, 0x05125DAD, 0x1642AE59, 0xE4292D5A,
            0xBA3A117E, 0x4851927D, 0x5B016189, 0xA96AE28A,
            0x7DA08661, 0x8FCB0562, 0x9C9BF696, 0x6EF07595,
            0x417B1DBC, 0xB3109EBF, 0xA0406D4B, 0x522BEE48,
            0x86E18AA3, 0x748A09A0, 0x67DAFA54, 0x95B17957,
            0xCBA24573, 0x39C9C670, 0x2A993584, 0xD8F2B687,
            0x0C38D26C, 0xFE53516F, 0xED03A29B, 0x1F682198,
            0x5125DAD3, 0xA34E59D0, 0xB01EAA24, 0x42752927,
            0x96BF4DCC, 0x64D4CECF, 0x77843D3B, 0x85EFBE38,
            0xDBFC821C, 0x2997011F, 0x3AC7F2EB, 0xC8AC71E8,
            0x1C661503, 0xEE0D9600, 0xFD5D65F4, 0x0F36E6F7,
            0x61C69362, 0x93AD1061, 0x80FDE395, 0x72966096,
            0xA65C047D, 0x5437877E, 0x4767748A, 0xB50CF789,
            0xEB1FCBAD, 0x197448AE, 0x0A24BB5A, 0xF84F3859,
            0x2C855CB2, 0xDEEEDFB1, 0xCDBE2C45, 0x3FD5AF46,
            0x7198540D, 0x83F3D70E, 0x90A324FA, 0x62C8A7F9,
            0xB602C312, 0x44694011, 0x5739B3E5, 0xA55230E6,
            0xFB410CC2, 0x092A8FC1, 0x1A7A7C35, 0xE811FF36,
            0x3CDB9BDD, 0xCEB018DE, 0xDDE0EB2A, 0x2F8B6829,
            0x82F63B78, 0x709DB87B, 0x63CD4B8F, 0x91A6C88C,
            0x456CAC67, 0xB7072F64, 0xA457DC90, 0x563C5F93,
            0x082F63B7, 0xFA44E0B4, 0xE9141340, 0x1B7F9043,
            0xCFB5F4A8, 0x3DDE77AB, 0x2E8E845F, 0xDCE5075C,
            0x92A8FC17, 0x60C37F14, 0x73938CE0, 0x81F80FE3,
            0x55326B08, 0xA759E80B, 0xB4091BFF, 0x466298FC,
            0x1871A4D8, 0xEA1A27DB, 0xF94AD42F, 0x0B21572C,
            0xDFEB33C7, 0x2D80B0C4, 0x3ED04330, 0xCCBBC033,
            0xA24BB5A6, 0x502036A5, 0x4370C551, 0xB11B4652,
            0x65D122B9, 0x97BAA1BA, 0x84EA524E, 0x7681D14D,
            0x2892ED69, 0xDAF96E6A, 0xC9A99D9E, 0x3BC21E9D,
            0xEF087A76, 0x1D63F975, 0x0E330A81, 0xFC588982,
            0xB21572C9, 0x407EF1CA, 0x532E023E, 0xA145813D,
            0x758FE5D6, 0x87E466D5, 0x94B49521, 0x66DF1622,
            0x38CC2A06, 0xCAA7A905, 0xD9F75AF1, 0x2B9CD9F2,
            0xFF56BD19, 0x0D3D3E1A, 0x1E6DCDEE, 0xEC064EED,
            0xC38D26C4, 0x31E6A5C7, 0x22B65633, 0xD0DDD530,
            0x0417B1DB, 0xF67C32D8, 0xE52CC12C, 0x1747422F,
            0x49547E0B, 0xBB3FFD08, 0xA86F0EFC, 0x5A048DFF,
            0x8ECEE914, 0x7CA56A17, 0x6FF599E3, 0x9D9E1AE0,
            0xD3D3E1AB, 0x21B862A8, 0x32E8915C, 0xC083125F,
            0x144976B4, 0xE622F5B7, 0xF5720643, 0x07198540,
            0x590AB964, 0xAB613A67, 0xB831C993, 0x4A5A4A90,
            0x9E902E7B, 0x6CFBAD78, 0x7FAB5E8C, 0x8DC0DD8F,
            0xE330A81A, 0x115B2B19, 0x020BD8ED, 0xF0605BEE,
            0x24AA3F05, 0xD6C1BC06, 0xC5914FF2, 0x37FACCF1,
            0x69E9F0D5, 0x9B8273D6, 0x88D28022, 0x7AB90321,
            0xAE7367CA, 0x5C18E4C9, 0x4F48173D, 0xBD23943E,
            0xF36E6F75, 0x0105EC76, 0x12551F82, 0xE03E9C81,
            0x34F4F86A, 0xC69F7B69, 0xD5CF889D, 0x27A40B9E,
            0x79B737BA, 0x8BDCB4B9, 0x988C474D, 0x6AE7C44E,
            0xBE2DA0A5, 0x4C4623A6, 0x5F16D052, 0xAD7D5351,
    };

    private static final long LONG_MASK = 0xFFFFFFFFL;
    private static final int BYTE_MASK = 0xFF;

    private int crc = ~0;

    @Override
    public void update(int b) {
        crc = crc32c(crc, b);
    }

    @Override
    public void update(byte[] buffer, int offset, int length) {
        for (int i = offset; i < offset + length; i++) {
            crc = crc32c(crc, buffer[i]);
        }
    }

    @Override
    public long getValue() {
        return (crc ^ LONG_MASK) & LONG_MASK;
    }

    @Override
    public void reset() {
        crc = ~0;
    }

    private static int crc32c(int crc, int b) {
        return crc >>> 8 ^ CRC_TABLE[(crc ^ b & BYTE_MASK) & BYTE_MASK];
    }
}

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