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102 lines
3.7 KiB
C#
102 lines
3.7 KiB
C#
/*
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* Copyright 2018 faddenSoft
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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using System;
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using System.Diagnostics;
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using System.IO;
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namespace CommonUtil {
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/// <summary>
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/// Compute a standard CRC-32 (polynomial 0xedb88320, or
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/// x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x+1).
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/// </summary>
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public static class CRC32 {
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private static readonly uint[] sTable = ComputeTable();
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private const uint INVERT = 0xffffffff;
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/// <summary>
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/// Generates 256-entry CRC table.
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/// </summary>
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/// <returns>Table.</returns>
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private static uint[] ComputeTable() {
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uint[] table = new uint[256];
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uint poly = 0xedb88320;
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for (int i = 0; i < 256; i++) {
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uint val = (uint) i;
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for (int j = 0; j < 8; j++) {
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val = (val & 1) != 0 ? poly ^ (val >> 1) : val >> 1;
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}
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table[i] = val;
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}
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return table;
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}
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/// <summary>
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/// Computes a CRC-32 on part of a buffer of data.
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/// </summary>
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/// <param name="crc">Previously computed CRC value. Use zero as initial value.</param>
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/// <param name="buffer">Data to compute CRC on.</param>
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/// <param name="offset">Start offset within buffer.</param>
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/// <param name="count">Number of bytes to process.</param>
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/// <returns>Computed CRC value.</returns>
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public static uint OnBuffer(uint crc, byte[] buffer, int offset, int count) {
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crc = crc ^ INVERT;
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while (count-- != 0) {
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crc = sTable[(crc ^ buffer[offset]) & 0xff] ^ (crc >> 8);
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offset++;
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}
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return crc ^ INVERT;
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}
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/// <summary>
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/// Computes a CRC-32 on a buffer of data.
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/// </summary>
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/// <param name="crc">Previously computed CRC value. Initially zero.</param>
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/// <param name="buffer">Data to compute CRC on.</param>
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/// <returns>Computed CRC value.</returns>
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public static uint OnWholeBuffer(uint crc, byte[] buffer) {
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return OnBuffer(crc, buffer, 0, buffer.Length);
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}
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/// <summary>
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/// Computes a CRC-32 on an entire file. An exception will be thrown on file errors.
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/// </summary>
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/// <param name="pathName">Full path to file to open.</param>
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/// <returns>Computed CRC value.</returns>
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public static uint OnWholeFile(string pathName) {
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using (FileStream fs = File.Open(pathName, FileMode.Open, FileAccess.Read)) {
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byte[] buffer = new byte[8192];
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uint crc = 0;
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long remain = fs.Length;
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while (remain != 0) {
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int toRead = (remain < buffer.Length) ? (int)remain : buffer.Length;
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int actual = fs.Read(buffer, 0, toRead);
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if (toRead != actual) {
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throw new IOException("Expected " + toRead + ", got " + actual);
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}
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crc = OnBuffer(crc, buffer, 0, toRead);
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remain -= toRead;
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}
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return crc;
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}
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}
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}
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}
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