Simplest way to calculate amount of even numbers in given range

Question

What is the simplest way to calculate the amount of even numbers in a range of unsigned integers?

An example: if range is [0...4] then the answer is 3 (0,2,4)

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Answer 1

I'm a bit surprised that iteration was tried to solve this. The minimum number of even numbers possible in a range is equal to half of the length of the array of numbers, or, rangeEnd - rangeStart.
Add 1 if the first or last number is even.

So the method is: (using javascript)

function evenInRange(rangeStart, rangeEnd)
{
  return
    Math.floor(rangeEnd - rangeStart) + 
    ((rangeStart % 2 == 0) || (rangeEnd % 2 == 0) ? 1 : 0)
}


Tests:
0 1 2 3 4 5 6 7 8
8 - 0 = 8
8 / 2 = 4
4 + 1 = 5
Even numbers in range:
0 2 4 6 8

11 12 13 14 15 16 17 18 19 20
20 - 11 = 9
9 / 2 = 4
4 + 1 = 5
Even numbers in range
12 14 16 18 20

1 2 3
3 - 1 = 2
2 / 2 = 1
1 + 0 = 1
Even numbers in range
2

2 3 4 5
5 - 2 = 3
3 / 2 = 1
1 + 1 = 2
Even numbers in range
2 4

2 3 4 5 6
6 - 2 = 4
4 / 2 = 2
2 + 1 = 3
Even numbers in range
2 4 6