struct AMOUNT_INFO { 
	unsigned time;
	int amount;
};
class CharacterInfo {
	// ...
	int ATKPercent, DEFPercent, MATKPercent, MDEFPercent;
}
class CPCBattle {
	// ...
	std::map<int, AMOUNT_INFO> m_ATKPercentList; // key = skid
};
void CPCBattle::SetATKPercentInfo(_SKILL_ID skid, unsigned duration, int val)
{
	auto info = &m_pc->m_characterInfo;
	
	auto entry = info.find(skid);
	if (auto entry = m_ATKPercentList.find(skid); entry != m_ATKPercentList.end())
	{
		auto entry_amount = entry->second.amount;
		if (std::abs(val) < std::abs(entry_amount))
			return;
		info->ATKPercent -= entry_amount;
	}
	
	auto stored = info->ATKPercent;
	if (stored + val < 0)
		val = -stored;
	
	unsigned timeout = 9999;
	info->ATKPercent = val + stored;
	if (duration != 9999)
		timeout = timeGetTime() + duration;
	
	auto pair = m_ATKPercentList[skid];
	pair->time = timeout;
	pair->amount = val;
	Trace("%s's ATKPercent: %d\n", info->characterName, info->ATKPercent);
	m_pc->NotifyParameter(VARR_ATTPOWER, 0);
}