utilities（C/C++）

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

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;
}