sdbmhash函数

unsigned int (char *str)
{
        unsigned int hash = 0;
        while(*str) {
                
                // 左移n,就是乘以2的n次方
                // hash * 64 + hash * 65536 - hash
                hash = (*str++) + (hash << 6) + (hash << 16) - hash;
        }
        return hash & 0x7FFFFFFF;
}