Negative MDEF should not increase damage from magic

[flamefury]

• rAthena Hash: 046d2e6
• Client Date: Doesn't matter
• Server Mode: Renewal
• Description of Issue:
  • Result: Having negative hard MDEF will increase the damage you take from enemy magic attacks.
  • Expected Result: Negative hard MDEF should be treated as 0 hard MDEF
  • How to Reproduce: Equip items that reduce hard MDEF and use Odin's Power + Assumptio to further magnify the effects.
  • Official Information: https://www.novaragnarok.com/forum/topic/7885-interaction-of-assumptio-odins-power-players-hard-mdef-and-monster-matk/?do=findComment&comment=39045
• Modifications that may affect results: None

[flamefury]

Some more proof without Assumptio:
AB soft MDEF = 41, hard MDEF = -18
Elder Willow MATK according to Divine-Pride: 43-52
Fire Bolt single hit damage: Low range of 2 to high range of 11

With 0 hard MDEF:

Damage = RANGE(43, 52) * (1000 + 0) / (1000 + 0 * 10) - 41
Damage = RANGE(43, 52) - 41
Damage = RANGE(2, 11)

If it was actually using -18 hMDEF, it would've looked like this instead:

Damage = RANGE(43, 52) * (1000 - 18) / (1000 - 180) - 41
Damage = RANGE(43, 52) * 982 / 820 - 41
Damage = RANGE(51, 62) - 41
Damage = RANGE(10, 21)

In other words, I should never see numbers 2-9 and should see numbers 12-21, but I see numbers in the low range and nothing higher than 11.

kRO replay file if you wish to check for equipment effects / shadow equipment.