value power two 

 1 /**
 2 *topPower2 use to set unsigned int to power of two
 3 *@param value input value
 4 *@return return the value's of the value,if input 3 return 4, if input 4 return 4
 5 */
 6 size_t topPower2(size_t value){
 7     if((value & (value-1)) == 0){
 8         return value;
 9     }    
10     unsigned long max_ulong = (unsigned long)((unsigned long)~0);
11     unsigned long mid = ~(max_ulong&(max_ulong>>1));
12     while((mid & value) == 0){
13         mid = mid>>1;
14     }
15     return mid<<1;
16 }

 

posted @ 2017-08-16 10:58  karllen  阅读(160)  评论(0)  编辑  收藏  举报