fix part of #H2343 - youmonst.movement vs poly

From a July 2011 report listing multiple movement anomalies, fix one
of the easier ones.  If you polymorph from a fast from into a slow
one, pending movement points can let the slow form get in some moves
it shouldn't.

I've deliberately avoided adjusting pending movement when you change
into a faster form, which will get it's own movement boost on the
next turn.

doc/fixes36.1

@@ -125,6 +125,7 @@ if a chameleon took vampire form, it would stop periodically changing shape
 corpses obtained from tipping an ice box wouldn't rot away
 suppress "you climb up the stairs" message if verbose option is off
 physical damage from mind flayer attack was being inflicted twice
+adjust pending movement points when polymorphing into a slower creature
 
 
 Platform- and/or Interface-Specific Fixes

src/mondata.c

@@ -13,6 +13,8 @@ struct monst *mon;
 struct permonst *ptr;
 int flag;
 {
+    int new_speed, old_speed = mon->data ? mon->data->mmove : 0;
+
     mon->data = ptr;
     if (flag == -1)
         return; /* "don't care" */
@@ -21,6 +23,15 @@ int flag;
         mon->mintrinsics |= (ptr->mresists & 0x00FF);
     else
         mon->mintrinsics = (ptr->mresists & 0x00FF);
+
+    if (mon->movement) { /* same adjustment as poly'd hero undergoes */
+        new_speed = ptr->mmove;
+        /* prorate unused movement if new form is slower so that
+           it doesn't get extra moves leftover from previous form;
+           if new form is faster, leave unused movement as is */
+        if (new_speed < old_speed)
+            mon->movement = new_speed * mon->movement / old_speed;
+    }
     return;
 }
 

src/polyself.c

@@ -42,6 +42,7 @@ void
 set_uasmon()
 {
     struct permonst *mdat = &mons[u.umonnum];
+    int new_speed, old_speed = youmonst.data ? youmonst.data->mmove : 0;
 
     set_mon_data(&youmonst, mdat, 0);
 
@@ -92,16 +93,23 @@ set_uasmon()
     PROPSET(PASSES_WALLS, passes_walls(mdat));
     PROPSET(REGENERATION, regenerates(mdat));
     PROPSET(REFLECTING, (mdat == &mons[PM_SILVER_DRAGON]));
+#undef PROPSET
 
     float_vs_flight(); /* maybe toggle (BFlying & I_SPECIAL) */
+    polysense();
 
-#undef PROPSET
+    if (youmonst.movement) {
+        new_speed = mdat->mmove;
+        /* prorate unused movement if new form is slower so that
+           it doesn't get extra moves leftover from previous form;
+           if new form is faster, leave unused movement as is */
+        if (new_speed < old_speed)
+            youmonst.movement = new_speed * youmonst.movement / old_speed;
+    }
 
 #ifdef STATUS_VIA_WINDOWPORT
     status_initialize(REASSESS_ONLY);
 #endif
-
-    polysense();
 }
 
 /* Levitation overrides Flying; set or clear BFlying|I_SPECIAL */