88 lines
2.1 KiB
C#
88 lines
2.1 KiB
C#
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using System;
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namespace VirtualNes.Core
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{
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public static class CRC
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{
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const int CHAR_BIT = 8;
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const uint CRCPOLY1 = 0x04C11DB7U;
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const uint CRCPOLY2 = 0xEDB88320U;
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static bool m_Init;
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static bool m_InitRev;
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static uint[] m_CrcTable = new uint[byte.MaxValue + 1];
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static uint[] m_CrcTableRev = new uint[byte.MaxValue + 1];
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public static ulong Crc(int size, Span<byte> c)
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{
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if (!m_Init)
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{
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MakeTable();
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m_Init = true;
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}
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ulong r = 0xFFFFFFFFUL;
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int step = 0;
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while (--size >= 0)
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{
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r = (r << CHAR_BIT) ^ m_CrcTable[(byte)(r >> (32 - CHAR_BIT)) ^ c[step]];
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step++;
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}
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return ~r & 0xFFFFFFFFUL;
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}
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public static uint CrcRev(int size, Span<byte> c)
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{
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if (!m_InitRev)
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{
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MakeTableRev();
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m_InitRev = true;
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}
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uint r = 0xFFFFFFFFU;
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int step = 0;
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while (--size >= 0)
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{
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r = (r >> CHAR_BIT) ^ m_CrcTableRev[(byte)r ^ c[step]];
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step++;
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}
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return r ^ 0xFFFFFFFFU;
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}
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static void MakeTable()
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{
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int i, j;
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uint r;
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for (i = 0; i <= byte.MaxValue; i++)
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{
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r = (uint)i << (32 - CHAR_BIT);
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for (j = 0; j < CHAR_BIT; j++)
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{
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if ((r & 0x80000000UL) > 0) r = (r << 1) ^ CRCPOLY1;
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else r <<= 1;
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}
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m_CrcTable[i] = r & 0xFFFFFFFFU;
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}
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}
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static void MakeTableRev()
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{
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int i, j;
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uint r;
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for (i = 0; i <= byte.MaxValue; i++)
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{
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r = (uint)i;
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for (j = 0; j < CHAR_BIT; j++)
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{
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if ((r & 1) > 0) r = (r >> 1) ^ CRCPOLY2;
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else r >>= 1;
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}
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m_CrcTableRev[i] = r;
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}
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}
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}
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}
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