Question

My binary search is for finding a position for ordered insertion in a std::vector. However, it seems to me that it is performing one (or more?) too many comparisons to find that position. Particularly the ternary at the end. Have I designed this wrong? To be clear, I haven’t noticed any errors in output.

template<typename T>
size_t find(std::vector<T> data, T value) //returns position value should be inserted at
{
 size_t start = 0;
 size_t end = data.size();

 if (!end) return 0;

 size_t diff;

 while (diff = (end - start) / 2)
 {
  size_t mid = diff + start;

  if (data[mid].value <= value)
  {
   start = mid;
  }
  else
  {
   end = mid;
  }
 }

 return data[start].value <= value ? end : start;
}

Answer 1

In a binary search, you fundamentally have a three-way branch:
>, < and =. There’s no way of writing this in C++ without
two comparison operators, but I would expect any decent compiler
to optimize them into a single machine instruction for the
comparison, followed by two conditional branches on the results.