add SAFE_DIV macro and usages

include/global.h

@@ -73,6 +73,14 @@
 #define abs(x) (((x) < 0) ? -(x) : (x))
 #endif
 
+// Used in cases where division by 0 can occur in the retail version.
+// Avoids invalid opcodes on some emulators, and the otherwise UB.
+#ifdef UBFIX
+#define SAFE_DIV(a, b) ((b) ? (a) / (b) : 0)
+#else
+#define SAFE_DIV(a, b) ((a) / (b))
+#endif
+
 // There are many quirks in the source code which have overarching behavioral differences from
 // a number of other files. For example, diploma.c seems to declare rodata before each use while
 // other files declare out of order and must be at the beginning. There are also a number of

src/battle_anim_mons.c

@@ -1706,7 +1706,7 @@ void SetBattlerSpriteYOffsetFromOtherYScale(u8 spriteId, u8 otherSpriteId)
 {
     s32 var = 64 - GetBattlerYDeltaFromSpriteId(otherSpriteId) * 2;
     u16 matrix = gSprites[spriteId].oam.matrixNum;
-    s32 var2 = (var << 8) / gOamMatrices[matrix].d;
+    s32 var2 = SAFE_DIV((var << 8), gOamMatrices[matrix].d);
 
     if (var2 > 128)
         var2 = 128;

src/battle_script_commands.c

@@ -3108,7 +3108,7 @@ static void atk23_getexp(void)
             calculatedExp = gBaseStats[gBattleMons[gBattlerFainted].species].expYield * gBattleMons[gBattlerFainted].level / 7;
             if (viaExpShare) // at least one mon is getting exp via exp share
             {
-                *exp = calculatedExp / 2 / viaSentIn;
+                *exp = SAFE_DIV(calculatedExp / 2, viaSentIn);
                 if (*exp == 0)
                     *exp = 1;
                 gExpShareExp = calculatedExp / 2 / viaExpShare;
@@ -3117,7 +3117,7 @@ static void atk23_getexp(void)
             }
             else
             {
-                *exp = calculatedExp / viaSentIn;
+                *exp = SAFE_DIV(calculatedExp, viaSentIn);
                 if (*exp == 0)
                     *exp = 1;
                 gExpShareExp = 0;

src/field_effect.c

@@ -3668,14 +3668,8 @@ static void Task_MoveDeoxysRock_Step(u8 taskId)
         data[5] = sprite->pos1.y << 4;
 
         // UB: Possible divide by zero
-        #ifdef UBFIX
-        #define DIVISOR (data[8] ? data[8] : 1);
-        #else
-        #define DIVISOR (data[8])
-        #endif
-
-        data[6] = ((data[2] << 4) - data[4]) / DIVISOR;
-        data[7] = ((data[3] << 4) - data[5]) / DIVISOR;
+        data[6] = SAFE_DIV(((data[2] << 4) - data[4]), data[8]);
+        data[7] = SAFE_DIV(((data[3] << 4) - data[5]), data[8]);
         data[0]++;
         // fallthrough
     case 1:

src/sprite.c

@@ -1333,7 +1333,7 @@ void ApplyAffineAnimFrameRelativeAndUpdateMatrix(u8 matrixNum, struct AffineAnim
 s16 ConvertScaleParam(s16 scale)
 {
     s32 val = 0x10000;
-    return val / scale;
+    return SAFE_DIV(val, scale);
 }
 
 void GetAffineAnimFrame(u8 matrixNum, struct Sprite *sprite, struct AffineAnimFrameCmd *frameCmd)