代码

int binary_search(const unsigned *a, int n, unsigned x)
{
	register unsigned l=0,r=n-1,mid,ans;
	while(l<=r)
	{
		mid=(l+r)>>1;
		if(a[mid]<=x)
		{
			ans=mid;
			l=mid+1;
		}
		else
		{
			r=mid-1;
		}
	}
	return ans;
}

评测结果