在二进制搜索中出错一次(角)

I'm having trouble with a corner case in my version of binary search. My version will output the bin which contains a 1 in the input list. The algorithm does this by testing groups of half the size of the input list respectively- upper and lower in the code below - and if the presence of a 1 is detected the algorithm moves the references around like a normal binary search and continues until it has found the 1. The list contains only 1s and 0s. I'm having trouble with a corner case in my ver