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

Let's look at this logically ...

We have four cases ...

odd -> odd     eg.  1 -> 3  answer: 1
odd -> even    eg.  1 -> 4  answer: 2
even -> odd    eg.  0 -> 3  answer: 2
even -> even   eg.  0 -> 4  answer: 3

The first three cases can be handled simply as ...

(1 + last - first) / 2

The fourth case does not fall quite so nicely into this, but we can fudge around a little bit for it quite easily ...

answer = (1 + last - first) / 2;
if (both first and last are even)
    answer++;

Hope this helps.