What controls why monsters/players cannot go below 0 MDB? (User error, it turns out they do indeed go below 0 as expected)

[ShiyoKozuki]

Monsters and players currently cannot go below negative MDB(its supposed to be 100 but it's 0 I think). When you go below 0 MDB it rolls over to a very high number and doesn't increase magic damage taken or reduce it.

[TeoTwawki]

When you go below 0 MDB it rolls over to a very high number

well that sounds like a pretty important bug o.O;;

[Xaver-DaRed]

Could you provide an example of MDB needing to be negative? Or something that would reduce MDB to a negative value?

I need more info.

[ShiyoKozuki]

MDB is supposed to be 100 base but it's coded as 0 here. Geo/indi-malaise reduces MDB up to -90.

[Xaver-DaRed]

MDB is supossed to be base 0.
The base "100" comes from the fact it's divided against MAB, wich is applied in magic.lua

mab = (100 + caster:getMod(xi.mod.MATT) + params.bonusmab) / (100 + target:getMod(xi.mod.MDEF) + mdefBarBonus)

[TeoTwawki]

Shiyo, what kinda damage/task did your char do to see it do this?

[ShiyoKozuki]

Despoil or omniscience. When I remove MDB from a mob and get it's MDB value it loops over to a huge number.

[zach2good]

What controls why monsters/players cannot go below 0 MDB?

A fun read for you!
Nuclear Gandhi

TLDR example:

• We model something using a type that can only hold 0-255.
• We start with 255
• We add 1
• It rolls over back to 0

The same thing happens in reverse!

• We model something using a type that can hold 0-4294967295
• We start with 2
• We subtract 3
• KAPOW: We're at 4294967295 D:

Since Lua models everything as doubles behind the scene, we can be sure that the problem isn't in Lua land. More likely: It's in a binding where we're trying to stuff some negative Lua value into an unsigned C++ integer type. Where that is: no idea.

EDIT:
Mod values are modelled this was: int16 m_amount{ 0 };

[ShiyoKozuki]

edit: I explained in a reply below better.

[Xaver-DaRed]

No. Not at all. Mobs are not supposed to have innate MDB unless it comes from a job trait. We already handle the "base 100" in magic.lua

[Xaver-DaRed]

So Shiyo, I tried testing this, but I could not reproduce it. I also looked arround the mess to see if I could find anywhere where it could be underflowing in such a manner.

Not saying I do not believe you, by any means, but would you be so kind to provide me the exact steps you took to test this? If you, for some reason cannot disclose them publicly, you can always send me a message to discord directly, not a problem.

[ShiyoKozuki]

Did you try removing mdb and mab from an enemy with default and then check its mdef/matt mod?

[ShiyoKozuki]

Okay I think I figured out the issue:
MDB and MAB for all entities(mob, player, pet, structures) is supposed to be set as "100" by default.
https://www.bg-wiki.com/ffxi/Magic_Damage#MAB.2FMDB:_Magic_Attack_Bonus_.2F_Magic_Defense_Bonus
We set it as "0". However, since magic.lua assumes MDB/MAB is default 100 the math for actually nuke actually maths out correctly from bonus MDB and MAB, but removing MDB/MAB off something with only base(0 in our case) MDB/MAB doesn't work correctly because the binding in c++ rolls over when going below 0. So the magic.lua formula goes 100 + casters mab(rolled over number) / 100 +targets mdb(rolled over number) and messes up things completely. The issue is the mod.

I think the solution is to move the 100 MDB/MAB from magic.lua and attach it to all entities instead as a bandaid. The real solution is checking why it's overflowing in c++ because int16_t can go to -32k.

Note: I"m using a GM command to get mdef/matt mod and to print it out in string format. It works perfectly for adding and removing MDB/MAB unless I am triyng to remove from base(0).

[TeoTwawki]

MDB and MAB for all entities(mob, player, pet, structures) is supposed to be set as "100" by default.

no it isn't

However, since magic.lua assumes MDB/MAB is default 100

no it doesn't, you are misreading the chunk of code that does the math. The 100 difference is handled internally to get math that matched BG without the user having to deal with this. a more thourough explanation will be along shortly by not me

[TeoTwawki]

Its gonna be me after all isn't it? -_-

When printing a signed value, you have to remember that while lua doesn't care what kind of number it is, string formatting to give you accurate output still does, if you use %u it will try to show you unsigned values. you need %i to see signed integer values. You aren't actually getting huge values of MDEF, your command you showed Xaver was using incorrection variables for its prints.

Try this instead
https://github.com/LandSandBoat/server/blob/4add91f29718b8485b07519a9f5111bf39097426/scripts/commands/getstats.lua

[ShiyoKozuki]

That fixes it, cool! Shows up as -10 now

[RAIST5150]

Not up to speed on all the various types... but I am guessing there is a specific reason to not use a "normal" INT type for the value that it would be able to go to a negative value?

[TeoTwawki]

modifiers are signed because we often need to deduct from their value rather than add.