二分查找

int binarySearch(int a[], int startIndex, int endIndex, const int target)
{
int left = startIndex;
int right = endIndex;
while(left <= right)
{
int middle = ((right - left) >> 1) + left;  //位运算提高效率，用减法防溢出。
if(a[middle] < target)      //对于指令流水，考虑分支预测，
left = middle + 1;
else if(a[middle] > target)
right = middle - 1;
else
return middle;
/*
bool flag = (target != a[middle]);
if(flag)    //分支可预测性增强，查找的最后一次才会预测失败
(a[middle] < target) ? (left = middle + 1) : (right = middle - 1);
else
return middle;
*/
}
return -1;
}