How does the Mutalisk's Glaive Bounce calculate damage?

Question

With zero upgrades and when attacking a unit with no armor, a Single mutalisk attack does:

• 9 Damage (first target)
• 3 Damage (second target)
• 1 Damage (third target)

What is less clear is what happens when armor and attack upgrades are researched? Does the damage expand to:

• 10 or 10
• 4 or 3.33
• 2 or 1.11

With 1 armor, how is the bounce damage reduced?

• 8 or 8 or 8
• 2 or 2.67 or 2.67
• 0 or 0.89 or 0.5

No other unit deals with fractional damage -- do Mutalisks do fractional damage, or does it get rounded down? Can Mutalisks do 0 damage with their bounce, or is there a minimum damage they will do with each attack?

Answer 1

Although it only displays whole numbers, the game tracks fractional damage internally.

For mutalisks, each upgrade level increases the first bounce by 1, the second bounce by 0.333 and the final bounce by 0.111.

Each point of armor simply subtracts 1 damage flat, however all attacks do a minimum of 0.5 damage, so with no attack upgrades and 1 armor it's 8 for the first bounce, 2 for the second and 0.5 for the final bounce.

Finally, mutalisks are not the only units that deal fractional damage. Several others do via splash damage or through bonus effects such as Corruption.