85 lines
2 KiB
C#
85 lines
2 KiB
C#
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namespace Uwaa.PNG;
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/// <summary>
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/// 32-bit Cyclic Redundancy Code used by the PNG for checking the data is intact.
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/// </summary>
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public static class Crc32
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{
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const uint Polynomial = 0xEDB88320;
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static readonly uint[] Lookup;
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static Crc32()
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{
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Lookup = new uint[256];
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for (uint i = 0; i < 256; i++)
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{
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var value = i;
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for (var j = 0; j < 8; ++j)
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{
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if ((value & 1) != 0)
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{
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value = (value >> 1) ^ Polynomial;
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}
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else
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{
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value >>= 1;
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}
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}
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Lookup[i] = value;
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}
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}
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/// <summary>
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/// Calculate the CRC32 for data.
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/// </summary>
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public static uint Calculate(byte[] data)
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{
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var crc32 = uint.MaxValue;
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for (var i = 0; i < data.Length; i++)
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{
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var index = (crc32 ^ data[i]) & 0xFF;
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crc32 = (crc32 >> 8) ^ Lookup[index];
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}
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return crc32 ^ uint.MaxValue;
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}
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/// <summary>
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/// Calculate the CRC32 for data.
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/// </summary>
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public static uint Calculate(List<byte> data)
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{
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var crc32 = uint.MaxValue;
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for (var i = 0; i < data.Count; i++)
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{
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var index = (crc32 ^ data[i]) & 0xFF;
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crc32 = (crc32 >> 8) ^ Lookup[index];
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}
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return crc32 ^ uint.MaxValue;
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}
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/// <summary>
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/// Calculate the combined CRC32 for data.
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/// </summary>
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public static uint Calculate(byte[] data, byte[] data2)
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{
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var crc32 = uint.MaxValue;
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for (var i = 0; i < data.Length; i++)
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{
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var index = (crc32 ^ data[i]) & 0xFF;
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crc32 = (crc32 >> 8) ^ Lookup[index];
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}
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for (var i = 0; i < data2.Length; i++)
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{
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var index = (crc32 ^ data2[i]) & 0xFF;
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crc32 = (crc32 >> 8) ^ Lookup[index];
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}
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return crc32 ^ uint.MaxValue;
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}
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}
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