How does the Mutalisk's Glaive Bounce calculate damage?

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?