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

The answer:

(max - min + 2 - (max % 2) - (min % 2)) / 2

A short explanation:

• even..even yields (length + 1) / 2
• even..odd yields length / 2
• odd..even yields length / 2

• odd..odd yields (length - 1) / 2

• length = max - min + 1

Therefore, the answer is (length - 1) / 2 plus 1/2 for even min plus 1/2 for even max. Note that (length - 1) / 2 == (max - min) / 2, and the "bonuses" are (1 - (min % 2)) / 2 and (1 - (max % 2)) / 2. Sum this all up and simplify to obtain the answer above.