d_hashf.h

来自「这是数据结构和算法的国外经典书籍.清华大学出版社出版的<数据结构C++语言」· C头文件 代码 · 共 76 行

#ifdef __BORLANDC__
// suppress the warning message that functions containing for are not
// expanded inline
#pragma warn -8027
// suppress the warning message about comparing signed and unsigned values
#pragma warn -8012
#endif	// __BORLANDC__

#ifndef HASH_FUNCTIONS

#define HASH_FUNCTIONS

#include <string>
#include <cmath>

using namespace std;

class hFintID
{
	public:
		unsigned int operator()(int item) const
		{ return (unsigned)item; }
};

class hFint
{
	public:
		unsigned int operator()(int item) const
		{
			unsigned int value = (unsigned int)item;

			value *= value;			// square the value
			value /= 256;				// discard the low order 8 bits
			return value % 65536;	// return result in range 0 to 65535
		}
};

class hFreal
{
	public:
		unsigned int operator()(double item) const
		{
			int exp;
			double mant;
			unsigned int hashval;

			if (item == 0)
				hashval = 0;
			else
			{
				mant = frexp(item,&exp);
				hashval = (unsigned int)((2 * fabs(mant) -1) * (unsigned int)~0);
			}
			return hashval;
		}
};

class hFstring
{
	public:
		unsigned int operator()(const string& item) const
		{
			unsigned int prime = 2049982463;

			int n = 0, i;

			for (i = 0; i < item.length(); i++)
				n = n*8 + item[i];

			return n > 0 ? (n % prime) : (-n % prime);
		}
};

#endif  // HASH_FUNCTIONS