DRY overflow-aware short addition

src/game/boe.specials.cpp

@@ -1483,9 +1483,7 @@ short damage_monst(cCreature& victim, short who_hit, short how_much, eDamageType
 	// Absorb damage?
 	if((dam_type == eDamageType::FIRE || dam_type == eDamageType::MAGIC || dam_type == eDamageType::COLD)
 		&& victim.abil[eMonstAbil::ABSORB_SPELLS].active && get_ran(1,1,1000) <= victim.abil[eMonstAbil::ABSORB_SPELLS].special.extra1) {
-		if(32767 - victim.health > how_much)
-			victim.health = 32767;
-		else victim.health += how_much;
+		add_check_overflow(victim.health, how_much);
 		ASB("  Magic absorbed.");
 		return false;
 	}

src/mathutil.hpp

@@ -9,6 +9,7 @@
 #pragma once
 
 #include <cmath>
+#include <climits>
 #include <SFML/System/Time.hpp>
 #include <random>
 
@@ -46,3 +47,9 @@ template<typename T>
 inline T sgn(T val) {
 	return val == 0 ? 0 : std::copysign(1, val);
 }
+
+inline void add_check_overflow(short& val, int how_much) {
+	if(SHRT_MAX - val > how_much)
+		val = SHRT_MAX;
+	else val += how_much;
+}

src/universe/creature.cpp

@@ -302,9 +302,7 @@ int cCreature::magic_adjust(int how_much) {
 	if(how_much <= 0) return how_much;
 	if(abil[eMonstAbil::ABSORB_SPELLS].active && get_ran(1,1,1000) <= abil[eMonstAbil::ABSORB_SPELLS].special.extra1) {
 		int gain = abil[eMonstAbil::ABSORB_SPELLS].special.extra2;
-		if(32767 - health > gain)
-			health = 32767;
-		else health += gain;
+		add_check_overflow(health, gain);
 		return 0;
 	}
 	// TODO: Magic resistance status effect?