88 lines
2.0 KiB
C++
88 lines
2.0 KiB
C++
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/************************************************************
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* crc16的checksum计算
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* 如果g_ulTable没有初始化，第一次使用的时候将初始化
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***********************************************************/
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#define CRC16_POLYNOMIAL 0x1021 // CRC_16校验方式的多项式.
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typedef unsigned char uchar;
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typedef unsigned int uint;
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typedef unsigned long ulong;
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static ulong g_ulTable[256];
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static bool has_inited = false;
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#include "_osdef.h"
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// CRC_16方式校验的初始化函数, 计算CRC_16余数表.
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void CRC16Init(void)
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{
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if (has_inited) return;
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uint nRemainder;
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int n, m;
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ulong *pulTable = g_ulTable;
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for(n = 0; n < 256; n ++)
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{
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nRemainder = (uint)n << 8;
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for(m = 8; m > 0; m --)
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{
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if(nRemainder & 0x8000)
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{
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nRemainder = (nRemainder << 1) ^ CRC16_POLYNOMIAL;
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}
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else
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{
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nRemainder = (nRemainder << 1);
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}
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}
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*(pulTable + n) = nRemainder;
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}
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has_inited =true;
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}
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// 反转数据的比特位, 反转后MSB为1.
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// 反转前: 1110100011101110 0010100111100000
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// 反转后: 1111001010001110 1110001011100000
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unsigned int CRCBitReflect(ulong ulData, int nBits)
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{
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ulong ulResult = 0x00000000L;
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int n;
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for(n = 0; n < nBits; n ++)
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{
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if(ulData & 0x00000001L)
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{
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ulResult |= (ulong)(1L << ((nBits - 1) - n));
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}
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ulData = (ulData >> 1);
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}
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return(ulResult);
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}
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// 以CRC_16方式计算一个数据块的CRC值.
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// pucData - 待校验的数据块指针.
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// nBytes - 数据块大小, 单位是字节.
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// 返回值是无符号的长整型, 其中低16位有效.
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unsigned int CRC16Calc( unsigned char *pucData, size_t nBytes)
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{
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uint nRemainder, nRet;
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uchar index;
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if (has_inited ==false)
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{
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CRC16Init(); //如果没有初始化就初始化以下
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}
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ulong *pulTable = g_ulTable;
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nRemainder = 0x0000;
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for(size_t n = 0; n < nBytes; n ++)
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{
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index = (uchar)CRCBitReflect(*(pucData + n), 8) ^ (nRemainder >> 8);
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nRemainder = (uint)*(pulTable + index) ^ (nRemainder << 8);
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}
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nRet = (uint)CRCBitReflect(nRemainder, 16) ^ 0x0000;
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return(nRet);
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}
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