Document berry yield

fix wording

include/berry.h

@@ -1,6 +1,8 @@
 #ifndef GUARD_BERRY_H
 #define GUARD_BERRY_H
 
+#define NUM_BERRY_STAGES 4
+
 void ClearEnigmaBerries(void);
 void SetEnigmaBerry(u8 *src);
 bool32 IsEnigmaBerryValid(void);

src/berry.c

@@ -1200,6 +1200,15 @@ static u8 GetNumStagesWateredByBerryTreeId(u8 id)
     return BerryTreeGetNumStagesWatered(GetBerryTreeInfo(id));
 }
 
+// Berries can be watered at 4 stages of growth. This function is likely meant
+// to divide the berry yield range equally into quartiles. If you watered the
+// tree n times, your yield is a random number in the nth quartile.
+//
+// However, this function actually skews towards higher berry yields, because
+// it rounds `extraYield` to the nearest whole number.
+//
+// See resulting yields: https://pastebin.com/RLGnP9Ng, and 
+// bug fix: https://pastebin.com/cDjnUWL0.
 static u8 CalcBerryYieldInternal(u16 max, u16 min, u8 water)
 {
     u32 randMin;
@@ -1215,10 +1224,11 @@ static u8 CalcBerryYieldInternal(u16 max, u16 min, u8 water)
         randMax = (max - min) * (water);
         rand = randMin + Random() % (randMax - randMin + 1);
 
-        if ((rand & 3) > 1)
+        // Round upwards
-            extraYield = rand / 4 + 1;
+        if ((rand % NUM_BERRY_STAGES) >= NUM_BERRY_STAGES / 2)
+            extraYield = rand / NUM_BERRY_STAGES + 1;
         else
-            extraYield = rand / 4;
+            extraYield = rand / NUM_BERRY_STAGES;
         return extraYield + min;
     }
 }