实验: FEC纠错编码的验证

// FecFixCode.cpp : Defines the entry point for the console application. // #include "stdafx.h" #include "FecFixCode.h" #ifdef _DEBUG #define new DEBUG_NEW #undef THIS_FILE static char THIS_FILE[] = __FILE__; #endif ///////////////////////////////////////////////////////////////////////////// // The one and only application object CWinApp theApp; using namespace std; const int const gFecCodeBitMask[15] = {0x1,0x2,0x4,0x8,0x10,0x20,0x40,0x80,0x100,0x200,0x365,0x1AF,0x35E,0x1D9,0x3B2}; /** gFecCodeBitMask[ 0] = 1, 00000000000000000000000000000001 gFecCodeBitMask[ 1] = 2, 00000000000000000000000000000010 gFecCodeBitMask[ 2] = 4, 00000000000000000000000000000100 gFecCodeBitMask[ 3] = 8, 00000000000000000000000000001000 gFecCodeBitMask[ 4] = 10, 00000000000000000000000000010000 gFecCodeBitMask[ 5] = 20, 00000000000000000000000000100000 gFecCodeBitMask[ 6] = 40, 00000000000000000000000001000000 gFecCodeBitMask[ 7] = 80, 00000000000000000000000010000000 gFecCodeBitMask[ 8] = 100, 00000000000000000000000100000000 gFecCodeBitMask[ 9] = 200, 00000000000000000000001000000000 gFecCodeBitMask[10] = 365, 00000000000000000000001101100101 gFecCodeBitMask[11] = 1af, 00000000000000000000000110101111 gFecCodeBitMask[12] = 35e, 00000000000000000000001101011110 gFecCodeBitMask[13] = 1d9, 00000000000000000000000111011001 gFecCodeBitMask[14] = 3b2, 00000000000000000000001110110010 */ //the check array int g_FecCodeCheck[5]={0x765,0x9AF,0x135E,0x21D9,0x43B2}; /** g_FecCodeCheck[ 0] = 765, 00000000000000000000011101100101 g_FecCodeCheck[ 1] = 9af, 00000000000000000000100110101111 g_FecCodeCheck[ 2] = 135e, 00000000000000000001001101011110 g_FecCodeCheck[ 3] = 21d9, 00000000000000000010000111011001 g_FecCodeCheck[ 4] = 43b2, 00000000000000000100001110110010 */ //---------------------------------------- //DWORD数值置位数组, //---------------------------------------- //置1常量数组, dwIn按位或dwSet1[n], 把dwIn的nBit置1 const DWORD const g_dwSet1[32] = { 0x00000001, 0x00000002, 0x00000004, 0x00000008, 0x00000010, 0x00000020, 0x00000040, 0x00000080, 0x00000100, 0x00000200, 0x00000400, 0x00000800, 0x00001000, 0x00002000, 0x00004000, 0x00008000, 0x00010000, 0x00020000, 0x00040000, 0x00080000, 0x00100000, 0x00200000, 0x00400000, 0x00800000, 0x01000000, 0x02000000, 0x04000000, 0x08000000, 0x10000000, 0x20000000, 0x40000000, 0x80000000,}; //置0常量数组 //置一常量数组, dwIn按位与dwSet0[n], 把dwIn的nBit置0 const DWORD const g_dwSet0[32] = { 0xfffffffe, 0xfffffffd, 0xfffffffb, 0xfffffff7, 0xffffffef, 0xffffffdf, 0xffffffbf, 0xffffff7f, 0xfffffeff, 0xfffffdff, 0xfffffbff, 0xfffff7ff, 0xffffefff, 0xffffdfff, 0xffffbfff, 0xffff7fff, 0xfffeffff, 0xfffdffff, 0xfffbffff, 0xfff7ffff, 0xffefffff, 0xffdfffff, 0xffbfffff, 0xff7fffff, 0xfeffffff, 0xfdffffff, 0xfbffffff, 0xf7ffffff, 0xefffffff, 0xdfffffff, 0xbfffffff, 0x7fffffff,}; static DWORD dwTimeBegin = 0; static DWORD dwTimeEnd = 0; int FecFixCode(BYTE ucIn); int printfData2Bits(DWORD dwIn); CString DwordToCString(DWORD dwIn); void TimeLogBegin(); void TimeLogEnd(); void showTimeLog(); /** @name: ChangValBit @function: 改变nBitPos指定位的值 @para: DWORD dwVal, 需要改变的值 @para: int nBitPos, 需要改变的位 @return: 返回改变后的值 @note: 纠错编码有14位(8+6), nBitPos = 0~13 */ DWORD ChangValBit(DWORD dwVal, int nBitPos); /** @name: FecFixCode_Encode @function: fec编码 @para: BYTE ucIn, 编码前数据 @para: DWORD & dwOut, 编码后数据 @return: S_OK, 成功; S_FALSE, 失败 */ int FecFixCode_Encode(BYTE ucIn, DWORD & dwOut); /** @name: FecFixCode_Decode @function: fec解码 @para: DWORD dwIn, 解码前数据 @para: BYTE & ucOut, 解码后数据 @para: int nErrorBit, 被纠正的位数 @return: 0, 函数执行成功, 校验成功, 直接取到原始数据; 1, 函数执行成功, 校验失败, 进行了纠错, 纠正成功, 得到了纠正后的原始数据; 2, 函数执行失败, 校验失败, 进行了纠错, 纠正失败, 无法得到原始数据; */ int FecFixCode_Decode(DWORD dwIn, BYTE & ucOut, int & nErrorBit); int _tmain(int argc, TCHAR* argv[], TCHAR* envp[]) { int nRetCode = 0; // initialize MFC and print and error on failure if (!AfxWinInit(::GetModuleHandle(NULL), NULL, ::GetCommandLine(), 0)) { // TODO: change error code to suit your needs cerr << _T("Fatal Error: MFC initialization failed") << endl; nRetCode = 1; } else { int n = 0; for(n = 0; n <= 0xff; n++) { //经过实验: //编码时间位0MS //解码时间是随机的, 大部分是0, 有些是15MS, 16MS FecFixCode((BYTE)n); } } getchar(); return nRetCode; } int printfData2Bits(DWORD dwIn) { //INT和DWORD都是4个字节 size_t nLenDw = sizeof(DWORD); int nLenBits = nLenDw * 8; int nBitCur = 0; int nBitPos = 0; printf("/n"); for(int n = 0; n < nLenBits; n++) { nBitPos = nLenBits - 1 - n; nBitCur = (dwIn >> nBitPos) & 1; if(1 == nBitCur) { printf("1"); } else if(0 == nBitCur) { printf("0"); } else { ASSERT(0); } } printf("/n"); return S_OK; } CString DwordToCString(DWORD dwIn) { CString csOut; size_t nLenDw = sizeof(DWORD); int nLenBits = nLenDw * 8; int nBitCur = 0; int nBitPos = 0; int nPosBegin = 16;//DWORD的4个字节中, 只有低15位有用 for(int n = nPosBegin; n < nLenBits; n++) { nBitPos = nLenBits - 1 - n; nBitCur = (dwIn >> nBitPos) & 1; if(1 == nBitCur) { csOut += "1"; } else if(0 == nBitCur) { csOut += "0"; } else { ASSERT(0); } } return csOut; } int FecFixCode(BYTE ucIn) { int nRc = 0; //对一个字节进行fec纠错编码 //实验结果: 8bits的数据要7bits的数据来纠正, 例如输入数据是: 0xff, 输出数据是0x30ff //如果15位中任意错1位, 能纠正过来; 错的位数 > 1位，不能被纠正 DWORD dwFecOut = 0; BYTE ucOut; int nErrBit = 0; printf("原文: [0x%2.2x]/n", ucIn); TimeLogBegin(); if(S_OK != FecFixCode_Encode(ucIn, dwFecOut)) { printf("编码失败/n"); return S_FALSE; } printf("正确的纠错编码: [0x%x]/n", dwFecOut); TimeLogEnd(); showTimeLog(); //逐位改变正确编码的每一位, 验证纠正效果 //低8位是数据位, 高7位是纠错编码位 //先校验正确的纠错编码 DWORD dwChangeToErr = 0; for(int n = -1; n < 15; n++) { dwChangeToErr = ChangValBit(dwFecOut, n); TimeLogBegin(); nRc = FecFixCode_Decode(dwChangeToErr, ucOut, nErrBit); printf("输入[0x%2.2x]=[%s]", dwChangeToErr, (LPSTR)(LPCSTR)DwordToCString(dwChangeToErr)); if(0 == nRc) { printf("解码正确, 原文:[0x%2.2x]/n", ucOut); } else if(1 == nRc) { printf("纠错成功, 原文是:[0x%2.2x], 被纠正的位[%d]/n", ucOut, nErrBit); } else { printf("解码失败/n"); ASSERT(0); } TimeLogEnd(); showTimeLog(); } return S_OK; } int FecFixCode_Encode(BYTE ucIn, DWORD & dwOut) { int i = 0; int j = 0; int nMaskCode = 0; int mid[15]; int code_out[15]; for(i = 0; i < 15; i++) { nMaskCode = ucIn & gFecCodeBitMask[i]; for(j = 0; j < 10; j++) { mid[j] = nMaskCode & 1; nMaskCode = nMaskCode >> 1; } code_out[i] = mid[0]; for(j = 1; j < 10; j++) code_out[i] = code_out[i] ^ mid[j]; } for(i = 14; i >= 0; i--) { if(1 == code_out[i]) { dwOut |= g_dwSet1[i]; } else if(0 == code_out[i]) { dwOut &= g_dwSet0[i]; } else { return S_FALSE; } } return S_OK; } int FecFixCode_Decode(DWORD dwIn, BYTE & ucOut, int & nErrorBit) {//decode and correct int i = 0; int j = 0; int nTmp = 0; int mid[15]; int code_out[15]; int check_out[5]; int errorflag = 0; int matchbit = 0; int matchflag = 0; int comparebit = 0; int nRc = 0; memset(mid, 0, sizeof(int) * 15); memset(check_out, 0, sizeof(int) * 15); //change the data received into bits nTmp = dwIn; for (i=0;i<15;i++) { code_out[i] = nTmp & 1; nTmp = nTmp >> 1; } //caculate the cheksum for(i = 0; i < 5; i++) { nTmp = dwIn & g_FecCodeCheck[i]; //get every bit of nTmp for(j = 0; j < 15; j++) { mid[j]= nTmp & 1; nTmp = nTmp >> 1; } check_out[i]=mid[0]; for(j = 1; j < 15; j++) check_out[i] = check_out[i]^mid[j]; /*add the bits in mode 2*/ } i = 0; errorflag = 0; //check if the check is all 0 do { if(check_out[i] == 1) { errorflag = 1; i = 5; } else i++; } while (i<5); if(errorflag == 1) { i = 0; matchbit = 100;//look for the same line do { j = 0; matchflag = 1; do { comparebit = (g_FecCodeCheck[j] >> i) & 1; //get the [j][i] bit of the array if(check_out[j] != comparebit) {//not coincident,jump out at once j = 5; matchflag = 0; } else j++; } while(j < 5); if(1 == matchflag) { matchbit = i; i = 15;//if found,jump out at once } else i++; } while(i < 15); if(matchbit <= 14) { //correct the error bit code_out[matchbit] = code_out[matchbit] ^ 1; //printf("第%d位数据出错!/n", matchbit + 1); nErrorBit = matchbit; nRc = 1; } else { //printf("错误但不可纠!/n"); nRc = 2; } } else { //printf("传输正确或错误不可检!/n"); nRc = 0; } for(i = 7; i >= 0; i--) { if(1 == code_out[i]) { ucOut |= g_dwSet1[i]; } else if(0 == code_out[i]) { ucOut &= g_dwSet0[i]; } else { return S_FALSE; } } return nRc; } DWORD ChangValBit(DWORD dwVal, int nBitPos) {//位取反 if(nBitPos < 0) return dwVal; DWORD dwTmp = dwVal & g_dwSet1[nBitPos]; if(dwTmp > 0) { dwTmp = dwVal & g_dwSet0[nBitPos]; } else if(dwTmp == 0) { dwTmp = dwVal | g_dwSet1[nBitPos]; } return dwTmp; } void TimeLogBegin() { dwTimeBegin = ::GetTickCount(); } void TimeLogEnd() { dwTimeEnd = ::GetTickCount(); } void showTimeLog() { /** The elapsed time is stored as a DWORD value. Therefore, the time will wrap around to zero if the system is run continuously for 49.7 days. */ printf("showTimeUsed: [%d]~[ %d]=[%d mS]/n", dwTimeBegin, dwTimeEnd, (dwTimeEnd - dwTimeBegin)); }

 

总结:

编码一个字节用时0MS(MS计时器看不出来), 可忽略

 

解码一个字节大部分时间为0MS(MS计时器看不出来), 有部分数据位15MS, 16MS.

如果是传大文件, 所花费的解码时间需要再验证.

 

通讯时传送的数据几乎大了一倍, 纠错编码中有7位纠错位, 8位数据位, 一位空闲位.

如果非要把空闲位去掉, 那在解码时，还要花时间做空闲位的处理.