utilities（C/C++）

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swap 的另一种实现

int max, min;n > m ? (max = n, min = m):(max = m, min = n);                    // 此时的三目运算符不在等号右侧，用于赋值，而是做一些操作

十进制的小数形式（单精度、双精度）与 IEEE 754 下的二进制形式的相互转化

IEEE 754——计算机中浮点数的表示方法

std::bitset<32> float2bits(float n){    _ULonglong nMem = *(unsigned __int64*)&n;    return std::bitset<32>(nMem);}std::bitset<64> double2bits(double n){    _ULonglong nMem = *(unsigned __int64*)&n;    return std::bitset<64>(nMem);}float bits2float(std::bitset<32>& bs){    return *(float*)&bs;}double bits2double(std::bitset<64>& bs){    return *(double*)&bs;}

hashString

unsigned long  cryptTable[0x500];void prepareCryptTable(){    unsigned long idx1, idx2, k;    unsigned long step = 0x100, n = 5;    unsigned long seed = 0x00100001;    for (idx1 = 0; idx1 < step; ++idx1)    {        for (idx2 = idx1, k = 0; k < 5; ++k, idx2 += step)        {            unsigned long tmp1, tmp2;            seed = (seed * 125 + 3) % 0x2aaaab;            tmp1 = (seed & 0xffff) << 0x10;            seed = (seed * 125 + 3) % 0x2aaaab;            tmp2 = (seed & 0xffff);            cryptTable[idx2] = (tmp1 | tmp2);        }    }}unsigned long hashString(char* lpszFileName, unsigned long dwHashType){    unsigned char* key = (unsigned char*)lpszFileName;    unsigned long seed1 = 0x7fed7fed, seed2 = 0xeeeeeeee;    int ch;    while (*key)    {        ch = toupper(*key++);        seed1 = cryptTable[(dwHashType << 8) + ch] ^ (seed1 + seed2);        seed2 = ch + seed1 + seed2 + (seed2 << 5) + 3;    }    return seed1;}

解释说明见十一、从头到尾解析Hash表算法。

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