Fixed Pre-Re SoftDEF Formula (#6766)

* Fixed Pre-Re SoftDEF Formula
* Fixes #6648

Note: This does not fix the order of processing which is also wrong, but at least the damage is official now in 1vs1 combat when if no item bonuses or status changes are involved that directly impact DEF.

src/map/battle.cpp

@@ -5668,13 +5668,14 @@ static void battle_calc_defense_reduction(struct Damage* wd, struct block_list *
 			def2 = 1;
 	}
 
-	//Vitality reduction from rodatazone: http://rodatazone.simgaming.net/mechanics/substats.php#def
+	//Damage reduction based on vitality
 	if (tsd) {	//Sd vit-eq
 		int skill;
 #ifndef RENEWAL
-		//[VIT*0.5] + rnd([VIT*0.3], max([VIT*0.3],[VIT^2/150]-1))
-		vit_def = def2*(def2-15)/150;
-		vit_def = def2/2 + (vit_def>0?rnd()%vit_def:0);
+		//Damage reduction: [VIT*0.3] + RND(0, [VIT^2/150] - [VIT*0.3] - 1) + [VIT*0.5]
+		vit_def = ((3 * def2) / 10);
+		vit_def += rnd_value(0, (def2 * def2) / 150 - ((3 * def2) / 10) - 1);
+		vit_def += (def2 / 2);
 #else
 		vit_def = def2;
 #endif