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stdext::hash_map使用字符串key

寰子 — Tue, 14 Aug 2012 12:40:00 GMT

stdext::hash_map使用字符�Ԍ��const char*�Q�做key的话�Q�不是只指定一个compare函数难么��单，要给定一个结构体�Q�其包括hash函数�Q�compare函数�Q�以�?#8220;桶设�?#8221;

struct StringCompare
{
//define hash function for strings
    enum
    {
        //parameters for hash table
        bucket_size = 4,  // 一个桶4byte长度�Q�因为sizeof(char*)=4�Q?/span>
        min_buckets = 8 // 最��存�?个桶
    };
    size_t operator()(const char* str) const
    {
        unsigned int seed = 131; // 31 131 1313 13131 131313 etc..
unsigned int hash = 0;
while (*str)
{
hash = hash * seed + (*str++);
}
return (hash & 0x7FFFFFFF);
    }
    bool operator()(const char *s1, const char* s2) const
    {
        if (strcmp(s1, s2) == 0)
        {
            return false;
        }
        else
        {
            return true;
        }
    }
};

然后

stdext::hash_map

寰子 2012-08-14 20:40 发表评论

各种字符串Hash函数比较

寰子 — Tue, 14 Aug 2012 12:32:00 GMT

得分�W�一�Q?/p>

// BKDR Hash Function
unsigned int BKDRHash(char *str)
{
    unsigned int seed = 131; // 31 131 1313 13131 131313 etc..
    unsigned int hash = 0;

    while (*str)
    {
        hash = hash * seed + (*str++);
    }

    return (hash & 0x7FFFFFFF);
}

得分�W�二�Q?/p>

// AP Hash Function
unsigned int APHash(char *str)
{
    unsigned int hash = 0;
    int i;

    for (i=0; *str; i++)
    {
        if ((i & 1) == 0)
        {
            hash ^= ((hash << 7) ^ (*str++) ^ (hash >> 3));
        }
        else
        {
            hash ^= (~((hash << 11) ^ (*str++) ^ (hash >> 5)));
        }
    }

    return (hash & 0x7FFFFFFF);
}

得分�W�三�Q?/p>

// DJB Hash Function
unsigned int DJBHash(char *str)
{
    unsigned int hash = 5381;

    while (*str)
    {
        hash += (hash << 5) + (*str++);
    }

    return (hash & 0x7FFFFFFF);
}

得分�W�四�Q?/p>

// JS Hash Function
unsigned int JSHash(char *str)
{
    unsigned int hash = 1315423911;

    while (*str)
    {
        hash ^= ((hash << 5) + (*str++) + (hash >> 2));
    }

    return (hash & 0x7FFFFFFF);
}

另外�Q�此处也有一��文章，其中提及(qi��ng)�?ji��n)另外几�U�效率也颇高的hash��法

http://programmers.stackexchange.com/questions/49550/which-hashing-algorithm-is-best-for-uniqueness-and-speed/145633#145633

寰子 2012-08-14 20:32 发表评论

同一坐标�p�M��Q�由��L��两点计算旋�{角度.

寰子 — Tue, 14 Aug 2012 12:28:00 GMT

double CCarNaviView::CalculateRotateAngle(CPoint pntBegin,CPoint pntNext)
{
    CPoint pntFirst(pntBegin);
    CPoint pntSecond(pntNext);

    double dRotateAngle = atan2(fabs(pntBegin.x-pntNext.x),fabs(pntBegin.y-pntNext.y));

    //如果下一点的横坐标大于前一�?在第一和第四象�?
    if (pntNext.x>=pntFirst.x)
    {
        //在第一象限(0<=dRotateAngle<=90)
        if (pntNext.y>=pntFirst.y)
        {
            //不做��M��处理
            dRotateAngle=dRotateAngle;
        }
        else
        {
            dRotateAngle=PI-dRotateAngle;
        }
    }
    else//(在第二和�W�三象限)
    {
        //�W�二象限
        if (pntNext.y>=pntFirst.y)
        {
            dRotateAngle=2*PI-dRotateAngle;
        }
        else//�W�三象限
        {
            dRotateAngle=PI+dRotateAngle;
        }
    }
    dRotateAngle = dRotateAngle * 180 / PI;
    return dRotateAngle;
}

�?/p>

寰子 2012-08-14 20:28 发表评论

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stdext::hash_map使用字符串key

各种字符串Hash函数比较

同一坐标�p�M���Q�由��L��两点计算旋�{角度.

同一坐标�p�M��Q�由��L��两点计算旋�{角度.