Finding the floor value in an array

Problem:


Given an sorted array of N distinct integers, find floor value of input 'key'. Say, A = {1, 2, 3, 5, 6, 8, 9, 10} and key = 7, we should return 6 as outcome.

How can I optimize my solution?

private static int CalclualteFloorValue(int[] _sortedarray, int l, int r, int key)
        {
            if (_sortedarray[l] == key)
                return -1;

            int m = -1;

            while (l<=r)
            {
                 m = (r+l)/ 2;

                if (_sortedarray[m] == key)
                {
                    return  _sortedarray[m - 1];

                }
                else if (_sortedarray[m] < key)
                {
                    l = m+1;
                }
                else
                {
                    r = m-1;
                }
            }

            return _sortedarray[m];

        }

  int _floorValue = CalclualteFloorValue(_sortedarray, 0, _sortedarray.Length - 1,7);

In terms of speed, your solution is about as optimized as it can get. In terms of readability, your solution has much room for improvement. I prefer readability over speed. You should try to make your code as readable as possible, then, if you have performance issues, search for bottlenecks using a profiler and optimize them. The method body of CalclualteFloorValue can be made into a one-liner, which happens to be slower but is much more readable.

private static int CalclualteFloorValue(int[] sortedArray, int key)
{
    return sortedArray.Last(x => x < key);
}

If you wish to keep the speed of your original solution and increase readability, there are many improvements you can make:

-
Have a consistent parameter naming convention. _sortedarray has an underscore, but the other parameter names don't. I prefer to only use underscores for variables declared within classes but not within methods.

-
_sortedarray should be lowerCamelCase. That is, sortedArray.

-
If l will always be zero and r will always be array length - 1, declare them in the method body. Don't make the method caller do unnecessary work.

-
Use descriptive variable names instead of single letters.

The beginning of the method will now look like this:

private static int CalclualteFloorValue(int[] sortedArray, int key)
{
    int left = 0;
    int right = sortedArray.Length - 1;

StackExchange Code Review Q#105039, answer score: 2